Insulated Concrete Form Walls 

Integrated With Mechanical 

Systems in a Cold Climate Test 

House

D. Mallay and J. Wiehagen

Home Innovation Research Labs

September 2014
NOTICE

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Insulated Concrete Form Walls Integrated With

Mechanical Systems in a Cold Climate Test House

Prepared for:

The National Renewable Energy Laboratory

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway

Golden, CO 80401

NREL Contract No. DE-AC36-08GO28308

Prepared by: 

Home Innovation Research Labs

Partnership for Home Innovation (PHI)

400 Prince George’s Blvd.

Upper Marlboro, MD 20774

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40335-04/Deliverable 3.1.2

September 2014
The work presented in this report does not represent 

performance of any product relative to regulated 

minimum efficiency requirements.

The laboratory and/or field sites used for this work are 

not certified rating test facilities. The conditions and 

methods under which products were characterized for 

this work differ from standard rating conditions, as 

described.

Because the methods and conditions differ, the reported 

results are not comparable to rated product performance 

and should only be used to estimate performance under 

the measured conditions.
iii

Contents

Contents...................................................................................................................................................... iii

List of Figures ............................................................................................................................................ iv

List of Tables ............................................................................................................................................... v

Definitions................................................................................................................................................... vi

Acknowledgments .................................................................................................................................... vii

Executive Summary................................................................................................................................. viii

1 Introduction and Background ............................................................................................................. 1

1.1 Problem Statement........................................................................................................................... 1

1.2 Project Overview ............................................................................................................................. 1

1.3 Relevance to Building America ....................................................................................................... 3

2 Technical Approach ............................................................................................................................. 5

2.1 Research Questions.......................................................................................................................... 5

2.2 Design Phase Analysis..................................................................................................................... 5

2.3 Wall Systems ................................................................................................................................... 5

2.4 Air Sealing ....................................................................................................................................... 7

2.5 HVAC Systems................................................................................................................................ 9

2.5.1 Duct Design ........................................................................................................................ 9

2.5.2 Load Calculations............................................................................................................. 10

2.5.3 Heating Fuel Selection...................................................................................................... 10

2.5.4 Simulated Carbon Factor Emissions................................................................................. 12

2.5.5 Heating System Comfort Considerations.......................................................................... 13

2.5.6 Equipment Selection ......................................................................................................... 14

2.5.7 HVAC and Wall System Performance ............................................................................. 15

2.5.8 Mechanical Ventilation..................................................................................................... 17

2.6 Plumbing........................................................................................................................................ 21

2.7 Electric .......................................................................................................................................... 23

2.8 Lighting and Appliances................................................................................................................ 24

3 Final Energy Solution Package Analysis ......................................................................................... 25

3.1 Energy Simulation Estimates......................................................................................................... 25

3.2 Energy Efficiency Cost Analysis................................................................................................... 27

4 Test Results ........................................................................................................................................ 29

5 Discussion........................................................................................................................................... 31

5.1 U.S. Department of Energy Challenge Home Certification........................................................... 31

5.2 Insulated Concrete Form Wall Implementation............................................................................. 31

5.3 Air Sealing and Insulation ............................................................................................................. 33

5.4 Hot Water....................................................................................................................................... 35

5.5 Lighting.......................................................................................................................................... 36

5.6 Heating and Cooling Design.......................................................................................................... 36

5.7 Mechanical Ventilation Design...................................................................................................... 37

6 Conclusions ........................................................................................................................................ 39

6.1 Research Questions........................................................................................................................ 39

6.2 Key Findings and Lessons Learned ............................................................................................... 41

Appendix A: House Plans ........................................................................................................................ 45

Appendix B: Solar Thermal System Rating............................................................................................ 48
iv

List of Figures

Figure 1. NCTH: LCCTC Green Home 3 .................................................................................................... 2

Figure 2. LCCTC Green Home 1 ................................................................................................................ 2

Figure 3. LCCTC Green Home 2 ................................................................................................................ 2

Figure 4. NCTH: LCCTC Green Home 3 .................................................................................................... 3

Figure 5. Apprentice Green Community Mount Joy, Pennsylvania....................................................... 3

Figure 7. Duct system Installed in basement......................................................................................... 10

Figure 8. Simplified central return inside framed duct chase .............................................................. 10

Figure 9. Cost comparison for heating fuel sources............................................................................. 11

Figure 10. Carbon factor estimates for different heating fuel types.................................................... 13

Figure 11. Energy use comparison of ICF to light-frame wall system ................................................ 16

Figure 12. Hourly HVAC energy for light frame and ICF wall systems................................................ 17

Figure 13. Energy cost optimization simulation results ....................................................................... 25

Figure 14. Simulation source energy results ......................................................................................... 27

Figure 15. Floor framing........................................................................................................................... 32

Figure 16. House wrap installed before summer break ........................................................................ 32

Figure 17. Window flashing...................................................................................................................... 32

Figure 18. Door step details..................................................................................................................... 33

Figure 19. Foam over rough wiring at ICF.............................................................................................. 33

Figure 20. Basement drywall ................................................................................................................... 33

Figure 21. Fireplace bump-out................................................................................................................. 34

Figure 22. Framed gable before air sealing and insulation .................................................................. 34

Figure 23. Framed gable after air sealing and insulation ..................................................................... 34

Figure 24. Knee wall air barrier................................................................................................................ 34

Figure 25. Knee wall insulation ............................................................................................................... 35

Figure 26. Sealed top plate....................................................................................................................... 35

Figure 27. Sealed air barrier at the HVAC duct chase........................................................................... 35

Figure 28. Insulation dam at attic access............................................................................................... 35

Figure 29. Solar hot water storage tank and PEX piping manifold...................................................... 36

Figure 30. High efficacy lighting in the kitchen ..................................................................................... 36

Figure 31. Short and direct bath exhaust fan duct................................................................................ 37

Figure 32. Bath exhaust duct termination at soffit................................................................................ 37

Figure 33. Dedicated “stale” air duct in living room ............................................................................. 38

Figure 34. ICF display in the garage (sales/education office) of the NCTH ........................................ 42

Unless otherwise noted, all figures were created by Home Innovation Research Labs.
v

List of Tables

Table 1. Air Sealing Critical Areas............................................................................................................. 8

Table 2. Heating and Cooling Load Calculations Summary................................................................. 10

Table 3. Estimated Heating and Cooling Cost Summary...................................................................... 12

Table 4. HVAC Equipment Schedule....................................................................................................... 15

Table 5. Whole-House Mechanical (Fresh Air) Ventilation Design Data ............................................. 19

Table 6. Mechanical Ventilation Design Data......................................................................................... 20

Table 7. Summary of Annual Hot Water System Energy Supply and Use .......................................... 22

Table 8. Annual Estimates for Water Heating System Options............................................................ 23

Table 9. Simulation Source Energy Summary ....................................................................................... 26

Table 10. LCCTC Green Home 3 Revised Cost Analysis ...................................................................... 28

Table 11. Home Innovation Test Results................................................................................................ 29

Table 12. DOE Challenge Home Mandatory Requirements .................................................................. 31

Unless otherwise noted, all tables were created by Home Innovation Research Labs.
vi

Definitions

ACCA Air Conditioning Contractors of America

ACH Air Changes per Hour

ASHP Air Source Heat Pump

BEoptTM Building Energy Optimization Program

CFL Compact Fluorescent Lamp

CFM Cubic Feet per Minute

CZ Climate Zone

DOE U.S. Department of Energy

DSHP Ductless Split Heat Pump

EF Energy Factor

EL Equivalent Length

EPS Expanded Polystyrene

ERV Energy Recovery Ventilator

FPM Feet per minute

FR Friction Rate

GSHP Ground Source Heat Pump

HPWH Heat Pump Water Heater

HSPF Heating Season Performance Factor

HVAC Heating Ventilation and Air Conditioning

ICF Insulated Concrete Form 

IECC International Energy Conservation Code

iwc Inches Water Column

LCCTC Lancaster County Career and Technology Center

LED Light-Emitting Diode

NCTH New Construction Test House

Pa Pascal

PEX Cross-Linked Polyethylene

SDHW Solar Domestic Hot Water

SEER Seasonal Energy Efficiency Ratio

SEF Solar Energy Factor

SF Solar Fraction

SRCC Solar Rating and Certification Corporation

TEL Total Equivalent Length
vii

Acknowledgments

Home Innovation Research Labs acknowledges the U.S. Department of Energy Building 

America Program for sponsoring this research. A special thanks to Lancaster County Career and 

Technology Center for participating in this research project.
viii

Executive Summary

Transitioning from standard light frame to a thermal mass wall system in a high performance 

home will require a higher level of design integration with the mechanical systems. The much 

higher mass in the insulated concrete form (ICF) wall influences heat transfer through the wall 

and affects how the heating and cooling system responds to changing outdoor conditions. This is 

even more important for efficient, low-load homes with efficient heat pump systems in colder 

climates where the heating and cooling peak loads are significantly different. 

With the support of the U.S. Department of Energy Building America Program, Home 

Innovation Research Labs partnered with Lancaster County Career and Technology Center 

(LCCTC) to build a new construction test house (NCTH) in the cold climate of south central 

Pennsylvania (International Energy Conservation Code climate zone 5A [CZ 5A]) using ICF 

high mass wall construction. This research compares ICF construction to the increasingly 

complex frame walls and foundation walls of high performance houses in cold climates and 

evaluates the integration of the mechanical systems for energy performance and air distribution. 

The NCTH cost-effectively achieved 40% whole-house energy savings, U.S. Department of 

Energy Challenge Home certification, and National Green Building Standard gold level 

certification. All of the project goals support the educational efforts at LCCTC, a vocational high 

school where students gain practical experience building real houses that incorporate state-ofthe-art energy efficiency and green technologies.

This report encompasses a range of design features and component performance estimates in an 

effort to select practical, cost-effective solutions for high performance homes in a cold climate. 

Of primary interest is the influence of the ICF walls on developing an effective air sealing 

strategy and selecting heating and cooling equipment type and capacity. The domestic water 

heating system is analyzed for costs and savings to investigate options for higher efficiency 

electric water heating. A method to ensure mechanical ventilation airflows is examined. The 

final solution package includes high-R mass walls, very low infiltration rates, multistage heat 

pump heating, solar thermal domestic hot water system, and energy recovery ventilation.

This solution package can be used for homes to meet or exceed 2012 International Energy 

Conservation Code requirements throughout all CZs. The high mass wall construction system 

can enhance green benefits such as durability and reduced construction waste. 

Key findings from the design analysis show that:

● The ICF walls exceed building code wall performance requirements for all CZs and the 

R-value is similar to 2 × 6 light-frame wall systems with 1 in. of exterior insulation; the 

ICF walls cost more but were practical to build and deemed cost effective as a component 

of the overall energy solution package.

● Simulated hourly energy use of an ICF wall compared with a light-frame wall system of 

the same R-value during a very cold period in the heating season shows an average of 9% 

less annual energy use and as much as a 30% energy use reduction for a given hour 

period.
ix

● Annual energy costs for the high efficiency air source heat pump nearly equal that of high 

efficiency natural gas heating and are 30% lower than those for high efficiency propane 

fuel heating.

● Carbon factor, a metric often used to compare various fuels, for the high efficiency air 

source heat pump is nearly the same as for a high efficiency propane fuel; both are 

approximately 7% higher than that for natural gas, which is not available at the site. A

100-year value is used per ASHRAE Standard 105-2013.

● Based on standard heating, ventilation, and air conditioning sizing methodologies and in 

this climate, there is no significant difference in peak sizing for high mass and light frame 

wall systems of similar R-value, but two-stage heating and cooling equipment was 

selected to effectively respond to the expected thermal mass effects that increase the lowstage operation.

● Domestic water heating energy, based on simulation estimates, shows that the difference

in energy usage between a solar water heating system and a heat pump water heater is 

minimal, but there is about 5% additional household heating energy use and about a 1% 

household cooling energy savings with the heat pump water heater.

● The design analysis for the NCTH also evaluates the implementation and marketability of 

the solution package elements and uses construction cost estimates to find approximate 

return on investment. With current utility rates and an assumed 5% mortgage interest 

rate, the estimated cost premiums and utility savings are nearly equal to the increased 

mortgage costs before any interest savings or technology incentives are applied.

This report will support design efforts of builders and architects in evaluating options for wall 

systems, heating and cooling technology, and water heating systems applicable to the cold 

climate (CZ 5) and the mixed climate (CZ 4).
1

1 Introduction and Background

1.1 Problem Statement

Builders face increasingly complex decisions to meet energy efficiency demands. Recent energy 

codes and energy programs require higher levels of thermal insulation and air sealing. Tight and 

well-insulated buildings make effective mechanical systems more critical, but selecting more 

energy-efficient and complicated mechanical systems may be difficult to justify. Builders must 

evaluate and select systems that together meet energy savings goals and that are also durable and 

affordable. 

Insulated concrete form (ICF) wall construction is energy efficient and durable, but is often 

perceived as not cost effective compared to standard wall construction. ICF construction,

however, should be evaluated for energy performance and affordability with respect to the 

increasingly complex frame walls and foundation walls common in today’s high performance 

houses. 

Lower space conditioning loads require careful heating and cooling equipment selection and air 

distribution designs to ensure efficient operation and occupant comfort. Effective mechanical 

ventilation is important to help control humidity, air quality, and comfort, but tested airflows 

frequently do not meet design expectations. The relative energy use of domestic hot water is 

increased and presents an opportunity for additional energy savings. 

This research focuses on the interrelated performance of the ICF walls, air sealing strategy, and 

mechanical systems for a test house in a cold climate. This report compares ICF walls with the 

builder’s standard foundation and light frame walls, evaluates alternative heating fuels and 

equipment, examines a design method to ensure that mechanical ventilation system airflows 

meet design expectations, and analyzes alternative domestic water heating systems. Builders, 

particularly small builders, can benefit from this research when developing a final energy 

solution package. 

1.2 Project Overview

With the support of the U.S. Department of Energy (DOE) Building America Program, Home 

Innovation Research Labs (Home Innovation) partnered with Lancaster County Career and 

Technology Center (LCCTC) to build a third new construction test house (NCTH) (Figure 1) in 

Apprentice Green (LCCTC 2013), a community next to the school in Mount Joy, Lancaster 

County, Pennsylvania (International Energy Conservation Code [IECC] climate zone [CZ] 5A). 

LCCTC is a vocational high school with a Construction Technology program that prepares 

students for careers in the construction trades. The students gain practical experience building 

real houses that incorporate state-of-the-art energy efficiency and green technologies. Two 

homes are complete and occupied (Figure 2 and Figure 3). For the NCTH, construction began in 

September 2011 and was completed in June 2013 (Figure 4 and Figure 5; see floor plan in 

Appendix A).
2

Figure 1. NCTH: LCCTC Green Home 3

Figure 2. LCCTC Green Home 1 Figure 3. LCCTC Green Home 2

The single-family 2,384-ft2 (above grade) single-story house features ICF construction for the 

foundation and above-grade walls, a conditioned basement, vented attic, high levels of insulation 

and air sealing, and a detached garage (2-in. × 6-in., 24-in. on-center frame construction). 

Energy-efficient systems include a high efficiency air source heat pump (ASHP), ducts in 

conditioned space, energy recovery ventilator (ERV), thermal preheat solar domestic hot water 

(SDHW) system, cross-linked polyethylene (PEX) manifold plumbing distribution, and efficient 

lighting and appliances. Water efficiency is enhanced with a 3500-gallon rainwater collection 

and distribution system.

The overall program goals for the NCTH research project: 

• Develop a design to achieve 40% whole-house energy savings over the Building America 

B10 benchmark (the B10 benchmark is equivalent to meeting the 2009 IECC).

• DOE Challenge Home certification (DOE 2013).

• Document and evaluate costs for efficiency measures.

• National Green Building Standard gold level green certification (NGBS 2009).

Additional goals for the thermal enclosure and mechanical systems were established:
3

• Compare the construction process of ICF walls with builder standard walls.

• Compare the energy performance of ICF walls with builder standard walls.

• Develop an air sealing strategy to achieve a house tightness of 2 ACH50.

• Analyze the design and selection of heating and cooling system options most appropriate 

for ICF construction and this climate.

• Integrate the ERV with the heating and cooling air distribution system.

• Develop and evaluate a method to ensure measured mechanical ventilation system 

airflows meet design expectations.

Figure 4. NCTH: LCCTC Green Home 3 Figure 5. Apprentice Green Community

Mount Joy, Pennsylvania

1.3 Relevance to Building America

The goals for this project align well with the Building America goals to develop market ready 

solutions that improve energy efficiency (reduce home energy use by 30%–50% compared to 

2009 energy codes), durability, quality, affordability, and comfort (DOE 2012). 

ICF construction provides both structural and thermal components of the wall (Building America 

2013). Previous Building America research indicates that ICF walls above grade provide an 

effective high performance air barrier, reliable thermal performance, very good durability, and 

simplified interior and exterior finish attachments due to the embedded fastening strips (Smegal 

and Straub 2009; Straub 2010). ICF foundation walls compare favorably to high performance 

alternatives in terms of thermal control, durability, and constructability (BSC 2009; Smegal and

Straub 2010). Previous Building America research identifies recommended “high-R” wall 

performance targets in CZ-5: R-15 for foundation walls (R-20 in CZ-6, R-25 in CZ-7), and R30 

for above-grade walls (R-25 in CZ-4, R-35 in CZ-6, and R-40 in CZ-7) (Straub 2010). Based on 

these recommendations and common ICF specifications (R-22 assembly for this project), ICF 

construction would be considered “high-R” for foundation walls through CZ-6, and for abovegrade walls through CZ-3. Generally, ICF construction costs are noted as relatively high or high 

compared to standard construction, but did not include a cost analysis (Chasar et al. 2002; 

Desjarlais et al. 2002). 
4

This project compares ICF walls to the builder standard high performance walls. The combined 

energy performance of foundation and above-grade walls is compared to combined “high-R” 

recommendations to determine the overall energy comparison. The conventional vented attic and 

heating, ventilation, and air conditioning (HVAC) system allow for an isolated evaluation of ICF 

walls. This comparison will provide builders a more current comparison of ICF performance and 

affordability with respect to current wall systems in cold climates. 

The measured airflows of mechanical ventilation equipment are typically lower than design 

values due to an overly restrictive duct system. Anecdotal evidence suggests this issue persists

simply due to ignoring best practices. Manufacturer instructions, industry standards, and 

publications recognize the importance of sufficient duct layouts and provide suggested methods 

(ASHRAE 2010; Rudd 2009). But prescriptive duct sizing tables often use different design 

parameters than manufacturer’s performance data. The method presented in this report should be 

a relatively simple and effective tool for HVAC trade partners in all climates. 

The approach to evaluate heating fuel and hot water systems should be useful for builders and 

mechanical trade partners for all climates and particularly for houses without natural gas.
5

2 Technical Approach

2.1 Research Questions

Based on research gaps and project goals, the research questions for this project are:

1. How does the ICF wall system compare with the builder’s standard high performance 

foundation and framed wall systems in terms of estimated energy use?

2. How is the air sealing strategy different for ICF construction?

3. What are the heating and cooling design, selection, and performance issues and solutions 

that emerge based on the high performance ICF envelope design in CZ 5?

4. Are the proposed methods to ensure effective mechanical ventilation successful?

5. How do domestic hot water system design options compare in terms of energy savings 

and cost?

6. Are the elements of the energy efficiency package cost effective and market ready?

2.2 Design Phase Analysis

During the design phase, reviews were conducted between LCCTC, vendors, and Home 

Innovation. Home Innovation provided recommendations to improve air sealing, moisture 

management, and electrical installation specific to ICF construction. Home Innovation also 

provided heating and cooling load calculations (Air Conditioning Contractors of America 

[ACCA] Manual J), equipment selection, and duct design support. The major systems were 

evaluated for energy performance, durability, occupant comfort, and cost. LCCTC was 

committed to building the house with high performance features to exceed current energy code 

requirements (IECC 2009) and adhere to its green building philosophy. Notably, the educational 

component for students was consistently considered during this step. An iterative design process 

was used to evaluate the benefits and tradeoffs of alternative systems. For example, to select the 

best type of heating system, Home Innovation provided a detailed analysis of heating and 

cooling options for this low-load house. 

As a result of the design reviews, the plans were updated with new construction details and 

specifications. Goals and expectations were mutually agreed upon, and site reviews, inspections, 

and tests were scheduled for quality assurance. The analysis and selection of the major systems 

are described below. 

2.3 Wall Systems

LCCTC had previous success building ICF foundation walls and wanted to explore using ICF 

walls above grade to improve energy efficiency and sound attenuation. Sound attenuation was 

important because the NCTH is close to a gun club firing range. 

ICF construction provides both structural and thermal components of the wall. These walls are 

well insulated, inherently tight, and durable. The foam provides consistent thermal performance 

and minimizes thermal bridging. The concrete makes the walls air tight. Additionally, ICF walls 

are highly resistant to fire and wind. The thermal mass properties attenuate sound well and help 

create a uniform and stable temperature inside the house. 
6

ICF walls are usually built using rigid, insulating foam block forms that are stacked on site and 

remain in place after the concrete is poured. The concrete is reinforced with rebar that is installed 

as the blocks are stacked. The forms must be braced during concrete placement to prevent 

bulging and breakage. For this project, the forms consist of two 2 1⁄2-in. thick expanded 

polystyrene (EPS) foam panels separated 6 in. using polypropylene ties. The ties are imbedded in 

the foam 6 in. on center and provide attachment points for siding and drywall. The foam blocks 

are 48 in. wide, 16 in. high, and 11 in. deep. 

The decision to install ICF walls must take into account practical construction issues that are 

unique to ICF construction, and represent a change from most builders’ standard practices:

• ICF walls are generally poured one level at a time, and must be braced during concrete 

placement to prevent bulging and breakage.

• Sleeves for penetrations (utilities, ventilation ducts) should be installed before concrete.

• Electrical wiring in exterior walls requires either conduit within the forms before 

concrete, or wiring chases cut into the foam after concrete. 

• Waterproofing below grade is required.

• ICF walls are vapor retarders (the vapor permeance of EPS is 0.8–1.5 perms at 2 1⁄2-in.

thickness) and therefore the concrete requires an extended period of time to dry, so the 

interior and exterior wall coverings should allow drying to the interior and exterior 

(Smegal and Straub 2009).

• Pressure-treated wooden window and door bucks, if used, are installed before concrete.

• Deeper window and door jambs.

• Unfinished basements require a thermal barrier over the foam (e.g., drywall) for code 

prescribed fire resistance.

• Floor framing in multistory houses must be attached to the ICF assembly.

• The thermal mass properties may impact the sizing and operation of the heating and 

cooling system.

For this project the wall system had to meet, or preferably exceed, the prescriptive minimum 

insulation requirements of the 2012 IECC for CZ 5: 

• Wood frame wall: R 20 cavity, or R-13 cavity + R-5 continuous (same as 2009 IECC)

• Mass wall: R-13, or R-17 if more than half of the insulation is to the interior of the mass 

(same as 2009 IECC)

• Basement wall: R-15 continuous or R-19 cavity. (R-10 or R13 in 2009 IECC).
7

The ICF foundation walls1 are specified by the manufacturer at an R-22 based on 5 in. of EPS 

foam equally divided outside of a 6-in. concrete core (Figure 6).

Figure 6. ICF wall

A simple parallel path R-value calculation using the manufacturer’s stated EPS foam R-value of 

4.17/in. of foam thickness but without finishes or film factors calculates to R-21.5 for a clear 

wall section. This R-value for the foundation walls would satisfy 2012 IECC code requirements 

through all U.S. CZs and through CZ 6 based on recommendations for foundation walls (Straube 

2011). The R-value of the ICF above-grade wall will satisfy the 2012 IECC prescriptive 

requirements in all CZs based on mass wall minimum requirements. (High mass walls in the 

IECC have a lower R-value requirement than do low-mass walls.) When comparing the ICF wall 

system with a frame wall system, a parallel path calculation shows that a 2×6 wall with R-21 

cavity insulation, a framing factor of 20% and exterior insulation of R-5 has the same wall Uvalue as the ICF system, aside from any thermal mass benefit.

Given the ICF’s capability to provide sound attenuation2 and above-code thermal performance, 

ICFs were deemed valuable for this NCTH.

2.4 Air Sealing

There are few pathways through ICF walls for air leakage. This increases the relative importance 

of air sealing other critical areas. For this project, the ICF wall runs from the basement to the 

roofline; floor framing is connected to the concrete and within the thermal and air barrier of the 

building, eliminating this common leakage area found in standard frame construction. The 

critical areas for air sealing were window and door bucks, roof truss bearing plates, a framed 

attic knee-wall and exterior gable wall for the living room cathedral ceiling, the framed fireplace 

bump-out, a tray-ceiling in the dining room, and ceiling penetrations. 

 1 The ICF manufacturer is Reward Wall Systems, the specific product is the 11-in. iForm. 2 See for example www.structuremag.org/Archives/2007-8/C-BuildingBlocks-Doerr-August07.pdf for typical 

discussions of the sound attenuation benefits of ICF technology.
8

To achieve the house tightness goal of 2 ACH50, the team wanted to use readily available 

materials that can be installed by any trade contractor given a clear and concise list of air sealing 

details. Air sealing technologies were selected to achieve consistent and reliable results and 

simplify installation. A table was developed during the design phase to identify critical areas and 

specify air sealing products and methods (Table 1). This table was used in the field for quality 

assurance. Critical areas were sealed using one-part spray foam. Rigid foam boards were used as 

air barriers at knee walls.

Table 1. Air Sealing Critical Areas

Critical Area Locations To Be Air Sealed

(Implementation Details) Sealant

ICF Walls

a

Truss bearing plates (before drywall) Spray foamb

Rough openings of windows and doors Low-expansion 

spray foamc

Penetrations Spray foamb

Electrical rough-in cuts at forms, as needed Spray foamb

Ceiling Plane

Top of ICF walls (after drywall, from attic) Spray foamb

Top plates of partition walls (after drywall, from attic) Spray foamb

Penetrations (electrical boxes, exhaust fans, attic access) Spray foamb

Attic access panel (gasket, insulate R-10 minimum) Gasket

Dining room tray ceiling (install drywall air barrier at 

the ceiling and sides of tray before framing the tray)

Top of the HVAC central duct chase (framed cavity) Spray foamb

Framed Walls, 

Exterior

Fireplace bump-out (seal stud cavities at sheathing, top 

and bottom plates, and floor before insulation. Install 

and seal drywall air barriers behind and above fireplace 

after insulation)

Closed-cell 

spray 

polyurethane 

foamd

Living room cathedral ceiling gable (seal stud cavities 

at sheathing and top and bottom plates before 

insulation)

Spray foamb

Knee-Wall Air 

Barrier

Living room cathedral ceiling gable (install rigid foam 

air barrier, then seal stud cavities before insulation and

drywall

Spray foam1b

Framed Cavity 

Air Barriers

For this project, framed cavity air barriers have been 

addressed under Ceiling Plane above a All products in contact with the ICF must be compatible with EPS (i.e., no solvents)

b HILTI single-component polyurethane foam sealant, closed-cell, minimal expanding, fire-block, installed using 

application gun (or equivalent, such as Knauf EcoSeal spray applied elastomeric sealant, or such as DOW 

ENERFOAM Professional Foam Sealant) c HILTI sealant for window and door applications (or equivalent)

d Spray polyurethane foam: two-component polyurethane foam insulation and sealant, closed-cell.

Although the air sealing process is understood by many contractors whose work scope includes 

air sealing details, builder associates and ultimately the customer must also understand air 
9

sealing as an important part of the house design. The benefits of reducing air infiltration to the 

builder and customer include: 

• Provides excellent heating and cooling energy savings.

• Reduces potential for moisture migration.

• Optimizes insulation effectiveness.

• Helps improve comfort and indoor environmental quality.

• Reduces risk of ice dams.

• Conforms to increasing code requirements.

When discussing air sealing with builders, it is important that they understand air barriers and 

their function. Air barriers: 

• Prevent movement of air and moisture through the building thermal envelope.

• Must be continuous to be effective.

• Must be sealed to resist airflow and air pressure.

• Must be air impermeable (≤ 0.004 cfm/ft2 (0.02 L/s/SM) @ 75 Pa).

2.5 HVAC Systems

2.5.1 Duct Design

Installing the HVAC system entirely in conditioned space is a key early-on decision that must be 

made before performing heating and cooling load calculations. Installing systems in conditioned 

space provides significant heating and cooling energy savings by minimizing duct conduction 

and leakage losses. House leakage is reduced without register and grille penetrations through the 

building enclosure, and without the pressure drivers of leaky exterior ducts. Additionally, ducts 

in conditioned space may improve air quality (minimizes pollutants from attics, crawl spaces, 

and garages) and may contribute to smaller capacity systems. A simplified, compact duct layout 

can improve performance (reduced duct pressure losses) and further reduce energy losses and 

installed costs.

For the NCTH, the entire heating and cooling system (air handler and ducts) was designed to be 

installed in conditioned space. The air handler was installed in a central location in the basement. 

The duct board (R-4) supply trunk was installed in the basement next to the steel beam (Figure 

7), below and perpendicular to the floor joists. Metal (not insulated) supply branch ducts 

installed between the open-webbed floor joists serve perimeter floor registers upstairs and ceiling 

registers in the basement. Manual airflow balancing dampers were installed in each supply 

branch at the trunk. The simplified central return serving the upstairs was installed inside a 

framed duct chase that was suggested during the design phase and included in the revised plans 

(Figure 8). The duct system was designed in accordance with ACCA Manual D, after heating 

and cooling loads were calculated and equipment selected, including Table A1-1: Air Velocity 

for Noise Control (ACCA 2009). Bedroom transfer grilles, baffled to attenuate sound and light, 

provide return air pathways across closed doors in this compact return duct layout.
10

Figure 7. Duct system Installed in basement Figure 8. Simplified central return inside 

framed duct chase

2.5.2 Load Calculations

With the ducts entirely in conditioned space, the heating and cooling load calculations were 

performed in accordance with ACCA Manual J (ACCA 2006). The results are summarized in 

Table 2.

Table 2. Heating and Cooling Load Calculations Summary

Calculated Heat Loss Total Heat Loss 26,698 Btu/h

Calculated Heat Gain

Sensible heat gain 15,626 Btu/h

Latent heat gain 3,356 Btu/h

Total heat gain 18,982 Btu/h

The Manual J load calculations were developed for the high mass ICF wall system. Home 

Innovation substituted a light-frame 2 × 6 wall system with R-19 cavity insulation and R-4 

exterior insulation (having a similar R-value to that of the ICF wall system) that showed very 

little calculated load differences between the wall systems. However, because the Manual J 

calculation produces peak load values, it may not account for lower heating and cooling 

requirements anticipated due to the thermal effects of the high mass wall, and may miss an 

opportunity to further reduce equipment capacity. Thermal mass, even in cold climates, is 

expected to even out the demand for heating (or cooling) since the mass helps to regulate the 

indoor temperature by causing a dampened response to large changes in outdoor temperatures. 

This dampening effect can cause multi-stage heat pump equipment to operate in a lower stage for 

a longer period of time rather than switching into high speed for peak heating or cooling.

2.5.3 Heating Fuel Selection

Selecting the type of fuel for heating was an important decision for this project. For the two 

previous projects, LCCTC installed ground source heat pump (GSHP) systems, which were
11

acceptable, but the initial cost of a GSHP was deemed too expensive for this project. Instead, 

LCCTC initially considered propane gas because natural gas service is not available at the site 

and conventional ASHP technology has a negative perception locally as being costly to operate 

and uncomfortable. However, based on the following analysis, an ASHP system was ultimately 

selected.

Home Innovation conducted energy simulations (using the Building Energy Optimization 

Program [BEoptTM] software version 1.4 and the EnergyPlus simulation engine, BEoptE+ v1.4) 

to compare heating operating costs of a high efficiency propane gas furnace, natural gas furnace, 

and two different ASHP systems. A summary of the simulation is shown in Figure 9. The 

summary, which includes all energy uses in the home with the heating system fuel differences, 

indicates that, at these efficiencies and current fuel prices, the propane gas furnace costs 

significantly more to heat the house than the natural gas furnace or heat pump systems. 

Furthermore, the heating cost for the natural gas furnace is nearly the same as the ASHP for the 

NCTH. Although not available for this house location, natural gas is an option for other houses 

in the area and is included for reference.

Figure 9. Cost comparison for heating fuel sources

A summary of the heating and cooling costs (energy only, no fixed costs) of the propane gas 

system and the 16 seasonal energy efficiency ratio (SEER) ASHP is shown in Table 3. The result 

$0

$100

$200

$300

$400

$500

$600

$700

$800

$900

$1,000

$1,100

$1,200

$1,300

$1,400

$1,500

$1,600

$1,700

$1,800

$1,900

$2,000

$2,100

$2,200

$2,300

$2,400

$2,500

Propane (94%AFUE/16SEER) Natural Gas 

(94%AFUE/16SEER)

HP (13/7.7, 1-speed) HP (16/8.6, 2-speed)

Annual Cost based on Fuel Rates

Fuel Used for Heating

Hot Water (E)

Heating (P)

Heating (G)

Heating (E)

Cooling (E)

HVAC Fan/Pump (E)

Lights (E)

Lg. Appl. (E)

Vent Fan (E)

Misc. (E)

Propane at $3.36/gallon; Natural Gas at $1.26 per therm; Electricity at $0.127 per kWh

Propane $36.92 /Mbtu

Natural Gas $12.60 /Mbtu

Electrcity $37.22 /Mbtu
12

is an annual operating cost savings of about $640 for the ASHP. This simulation was confirmed 

by an independent operating cost estimate by the HVAC vendor that showed an annual operating 

cost savings of $625 for a 16 SEER, 8.4 heating season performance factor (HSPF) heat pump 

compared to a 94% annual fuel utilization efficiency propane gas furnace with a 16 SEER 

cooling system.

Table 3. Estimated Heating and Cooling Cost Summary

System

Annual 

Heating 

Energy Cost

Annual 

Cooling 

Energy Cost

Annual 

Blower 

Energy Cost

Total Annual 

Heating and 

Cooling Costs

ASHPa $389 $39 $17 $444

Gas Furnaceb (Propane) $1,018 $38 $28 $1,084 a Nominal 16 SEER, 8.6 HSPF heat pump

b Nominal 94% annual fuel utilization efficiency furnace and 16 SEER air conditioner

Beyond operating cost savings, by choosing an ASHP, LCCTC would save on the initial cost of 

a propane tank and gas piping. The cost of buying a 1000-gallon propane tank was quoted at 

$2,750 plus installation with a propane rate of $2.63/gallon. If the builder opted to lease a tank, 

the propane cost jumped to $3.48/gallon. With the lease option, it would take nearly 11 years to 

pay off the tank if purchased outright. Additionally, 100-gallon tanks were available for lease but 

not for sale, so the cost of propane would have been at the higher rate.

2.5.4 Simulated Carbon Factor Emissions

The goal of using the carbon factor estimates is to standardize the measurement and 

characterization of building energy performance. Using conversion factors from site energy use 

to carbon factor emissions (Deru and Torcellini 2007), global warming emissions estimates were 

compared for three fuel types. Whole-house energy consumption emissions estimates are 

presented; simulations were conducted by varying the heating and cooling system only. The 

heating systems that were compared include standard and high efficiency heat pump technology, 

high efficiency natural gas, and high efficiency propane fuels for heating. Results of simulated 

carbon dioxide emissions are presented in Figure 10.
13

Figure 10. Carbon factor estimates for different heating fuel types

The carbon factor for all systems are within 10% of each other with natural gas showing the 

lowest overall emission production. The high efficiency heat pump system with electricity fuel is 

nearly equal to the propane fueled heating system indicating that the use of electricity for heating 

at the higher efficiencies is an equivalent option to using on-site fuel.3

2.5.5 Heating System Comfort Considerations

Based on the builder and local market perception that conventional heat pumps do not deliver 

sufficiently high air temperatures in a cold climate to be comfortable, the builder initially did not 

want to install an ASHP. The issue was of sufficient concern that further investigation was 

performed to evaluate ASHP delivery temperature from the duct system.

Although a propane furnace generally delivers a higher supply air temperature than a heat pump 

system, modern heat pumps, due to advanced technology, provide somewhat warmer air than 

older heat pumps. For example, a high efficiency air handler (fan coil) often includes an 

electronically commutated motor, which can reduce fan speed during the heating mode, increase 

time that the air is in contact with the heating coil, and increase supply air discharge temperature 

 3 Due to transmission and distribution losses, electricity often results in a higher production of emissions (depending 

on the fuel used for generation) than burning fuel directly on-site for heating or other uses.

0

1

2

3

4

5

6

7

8

9

10

Propane 94% Natural Gas 94% HP (13/7.7, 1-speed) HP (16/8.6, 2-speed)

CO2equivalent Emissions, Metric Tons/year

Fuel Used for Heating

Hot Water (E)

Heating (P)

Heating (G)

Heating (E)

Cooling (E)

HVAC Fan/Pump (E)

Lights (E)

Lg. Appl. (E)

Vent Fan (E)

Misc. (E)
14

and improve comfort; the tradeoff is a marginal decrease in efficiency, because the heating and 

cooling capacity of direct expansion equipment is conditional on operating conditions and 

parameters including airflow. This comfort setting is similar to a dehumidification setting in the 

cooling mode. 

Equipment capacity can also affect comfort. The heating capacity of a conventional ASHP 

decreases as the outdoor air temperature drops. Heat pumps are typically sized to meet the 

cooling load and rely on supplemental electric heat, as needed, to meet the heating load. Heat 

pump systems with two-stage compressors (that commonly operate at two thirds capacity in lowstage) are more energy efficient and can improve comfort. For two-stage systems, low-speed 

operation normally provides improved dehumidification and comfort in the cooling mode. For 

colder climates, a two-stage system can be selected so that low-stage operation satisfies the 

cooling demand and high-stage operation meets most or all heating requirements This selection 

approach produces greater heating capacity, and reserve cooling capacity, but the tradeoff is less 

capacity for dehumidification during cooling (because there is only one stage for cooling) and 

the need for a larger duct system to accommodate the increased high-stage airflow. Residential 

two-stage equipment is generally available in 2-, 3-, 4-, or 5-ton capacities only (1-ton 

increments, and not 2.5- or 3.5-ton capacities; 1 ton of cooling equals 12,000 Btu/h).

Similarly, heat pump systems with inverter-technology compressors (variable speed compressors 

that ramp down to about 20% capacity) can be sized to meet the heating load in a colder climate 

and provide a steady heat output down to about 0°F (producing a relatively flat heating curve 

similar to a GSHP). In such a system, supplemental heat is generally reserved for comfort during

the defrost cycle. Inverter compressors ramp down to efficiently meet sensible and latent cooling 

requirements. This technology, common in ductless split heat pumps (DSHP), is particularly 

well-suited for cold climate applications.

2.5.6 Equipment Selection

After eliminating propane gas as cost prohibitive the team shifted its attention to selecting the 

most cost-effective ASHP technology. Inverter compressor technology applied to conventional 

ducted distribution systems was eliminated due to its initial cost and lack of availability through 

LCCTC’s preferred distributor. Inverter technology common in DSHP systems was not 

considered because LCCTC considers installing a conventional duct system an important 

educational aspect. The team selected a two-stage compressor heat pump, 16 SEER, 9.8 HSPF 

for optimum efficiency and performance. A 19 SEER system was ruled out because its rated 

heating performance was nearly identical to that of the selected, lower cost unit.

The equipment capacity was selected in accordance with ACCA Manual S (ACCA 2004). Using 

manufacturer product data for the selected model, the capacity was selected to meet the cooling 

loads in low-stage in order to improve the heating performance in high-stage. A 2-ton system had 

a heating balance point of approximately 30°F, but the selected 3-ton system provided additional 

heating capacity at design temperatures and a considerably better heating balance point of 

approximately 17°F. The total cooling capacity of the 3-ton system in low-stage is within the 

115% (any climate) and 125% (cold climate) over-sizing Manual S limits. The resulting HVAC 

equipment schedule is shown in Table 4.
15

Table 4. HVAC Equipment Schedule

Equipment Equipment Data

Heat Pump Amana ASZ160361, 3-ton, 2-stage, 16 SEER, 9.8 HSPF, 

American Heating and Refrigeration Institute # 4431376

Fan Coil Amana AVPTC31714, variable speed

Supplemental Heat Amana HKR-08C, 8 kW

Thermostat Amana CTK02BB Comfortnet

Filtration Minimum efficiency reporting value 13 media filter

Mechanical Ventilation Honeywell VNT5150E1000 and W8150 control

2.5.7 HVAC and Wall System Performance

This analysis is performed not so much to quantify energy savings (overall performance of the 

wall systems in this climate are very similar) but is more important for sizing the heating and 

cooling system and for determining the anticipated operation of two-stage equipment.

The selection of a high mass wall system impacts how the heating and cooling system will 

operate. Given that lumber density is about 28 lb/ft3 and concrete density is about 140 lb/ft3, a 

100-ft2 advanced frame wall system with about 20% framing factor has about 250 lb of mass 

compared with about 7,000 lb of mass in a 100-ft2 ICF wall. The much higher mass in the ICF 

wall influences the process of heat transfer across the wall system and affects how the HVAC

system responds to changing outdoor conditions. The thermal mass will slow the heat loss from 

the house since the mass reacts much less quickly to changing outdoor conditions. This thermal 

mass effect will generally cause the HVAC system to run in lower speed (given a multistage 

unit) but for a longer period of time.

Hourly estimated heating energy consumption for a light-frame wall system and an ICF wall of 

similar R-value is shown in Figure 11.
16

Figure 11. Energy use comparison of ICF to light-frame wall system

For most of the time during the select heating period, the simulation predicts less average hourly 

energy use for the ICF wall system than for the light-frame wall system. The thermal mass of the 

ICF walls is expected to mitigate larger shifts in energy use due to changing outdoor conditions 

due to the large heat storage capacity of the mass wall (compared with a light frame wall) The 

high heat capacity of the wall material dampens the heat flow across the wall system from indoor 

to outdoor (heating).The absolute difference, however, is not large for any hour during the 3-day 

analysis period.

A different view of the hourly simulation results indicate that, based on the simulation of heat 

transfer through the wall system, mass delays the response of heating energy usage to decreasing 

and increasing outdoor temperatures. The cumulative effect of this delay is shown in Figure 12,

which shows whole-house hourly energy difference between light-frame walls and ICF walls.

0

0.5

1

1.5

2

2.5

3

0

0.5

1

1.5

2

2.5

3

12:00 AM

2:00 AM4:00 AM6:00 AM8:00 AM

10:00 AM

12:00 PM

2:00 PM4:00 PM6:00 PM8:00 PM

10:00 PM

12:00 AM

2:00 AM4:00 AM6:00 AM8:00 AM

10:00 AM

12:00 PM

2:00 PM4:00 PM6:00 PM8:00 PM

10:00 PM

12:00 AM

2:00 AM4:00 AM6:00 AM8:00 AM

10:00 AM

12:00 PM

2:00 PM4:00 PM6:00 PM8:00 PM

10:00 PM

Hourly Average Electricity Use, kWh

Hourly Average Electrcity Use, kWh

Hourly, 3 days in February

Heat Pump Heating Energy Use Comparison, Simulation Data

Frame-HP, kWh ICF-HP, kWh
17

Figure 12. Hourly HVAC energy for light frame and ICF wall systems

The blue line plotted on the left axis in Figure 4 represents the cumulative difference in energy 

usage between the light-frame and ICF walls (Eframe – EICF). When the curve increases, the 

energy use of the ICF wall system is less than the frame wall system and opposite when the 

curve is decreasing. The rise of the cumulative energy difference is indicative of the ICF 

response to decreasing outdoor temperature (for which the stored thermal energy helps offset 

heating demand) and the decreasing cumulative energy difference indicates the response of the 

ICF walls to increasing outdoor temperature, in which the thermal mass is at a lower temperature 

than the outdoor air, and the heating system needs to continue to operate to provide heating to 

raise the thermal mass temperature. 

Even though the thermal mass at times may cause the heating or cooling system to operate longer 

than for a system in a light-frame house, the net result is that, based on simulations, the ICF wall 

system uses less energy than the frame wall system (both of similar R-values). 

2.5.8 Mechanical Ventilation

There are two types of mechanical ventilation. Source-exhaust mechanical ventilation, also 

known as local-exhaust and spot-exhaust, uses kitchen and bath exhaust fans ducted outdoors as 

the primary method to control moisture and odors. Whole-house mechanical ventilation, also 

-10

0

10

20

30

40

50

60

70

80

90

100

-10

0

10

20

30

40

50

60

70

80

90

100

Outdoor Temperature, F

Running Total Energy, kWh

Cumulative Energy Difference

Outdoor Temperature

Weekly Moving Average Outdoor Temperature
18

known as fresh-air ventilation, is the intentional exchange of “stale” indoor air with “fresh” 

outdoor air, at a controlled rate using fans. The purpose of whole-house mechanical ventilation is 

to improve indoor air quality, by diluting indoor contaminants (such as formaldehyde, cleaning 

agents, odors, allergens, and radon), which now take longer to dissipate in tighter houses, and 

helping to control relative humidity and moisture accumulation. The most recent building codes 

and above-code programs generally require whole-house mechanical ventilation. 

Measured airflows of installed mechanical ventilation products are frequently different than 

design values. Under-ventilation could jeopardize moisture control, occupant comfort, and 

building code or energy program compliance. Over-ventilation may lead to excessive energy use, 

occupant discomfort, and during some periods excessive indoor moisture levels. 

Based on numerous test sites, measured airflows are commonly lower than design values due to 

an overly restrictive duct system. An efficient duct layout will reduce airflow resistance and help 

ensure expected performance:

• Locate termination hoods to minimize duct lengths and number of elbows.

• Account for pressure drop of all components including termination hoods.

• Use manufacturer’s airflow and static pressure data; prescriptive duct sizing tables may 

use different static pressures.

• Increase duct diameter if necessary.

• Install rigid duct in place of flexible or corrugated duct as required.

• Install in accordance with manufacturer’s instructions.

A method to account for duct pressure drop is to apply the basic duct sizing principles described 

in ACCA Manual D commonly used for sizing heating and cooling air distribution ducts. The 

HVAC designer can simply apply these same principles to ventilation duct designs. This method 

is detailed below by way of example for the NCTH.

Interestingly, such a duct design is already technically required by code. The 2009 IRC, Section 

M1506.1, mandates that exhaust duct construction not specified in this chapter (bath exhaust fans 

and whole-house mechanical ventilation ducts are not) shall comply with Chapter 16. Section 

M1601.1 states that “duct systems serving heating, cooling and ventilation equipment shall be 

fabricated in accordance with the provisions of this section and ACCA Manual D or other 

approved methods.” Section M1601.4 mandates duct sealing.

For the NCTH, source-exhaust mechanical ventilation is provided by conventional kitchen range 

and bath exhaust fans (energy factor [EF]). Bath fans were specified for quiet performance and 

with timer controls to ensure adequate moisture removal. Whole-house mechanical ventilation is 

provided by an ERV. The ERV provides balanced ventilation and transfers a portion of the heat 

and moisture between the incoming fresh air and outgoing stale air streams. Installing an ERV is 

standard practice for LCCTC to ensure adequate indoor air quality. The team selected a twospeed ERV to provide continuous ventilation in accordance with ASHRAE 62.2-2010 

recommendations (ASHRAE 2010). 
19

An important goal for this project was to specify a design that effectively integrated the ERV 

with the heating and cooling duct distribution system. Incoming fresh air was ducted to the return 

plenum, so outdoor air is filtered and conditioned when the air handler is operating. The 

outgoing stale air was ducted from a dedicated grille in the living room; this approach avoids the 

“short-circuiting” of fresh air that occurs when both indoor and outdoor air ducts are installed in 

the return plenum and the air handler is not running. This partially integrated duct approach 

provides better fresh air distribution when the air handler is not running, and additionally 

provides a convenient grille to measure airflow using a standard flow hood. The ERV design 

criteria are shown in Table 5.

Table 5. Whole-House Mechanical (Fresh Air) Ventilation Design Data

Criteria NCTH

Conditioned Floor 

Area (ft2) 4,768 (2,384 above grade; 2,384 basement below grade)

Volume (ft3) 45,980 (including joist area and cathedral ceiling sections)

Bedrooms (Quantity) 3

Airflow Rate* (CFM) 78

1. Type

Balanced ERV

Partially integrated (fresh air to return trunk, stale air from single 

source (low-wall grille in living room; air handler has an 

electronically commutated motor). Duct to be rigid metal, short 

flexible sections at ERV, insulated ERV to outdoors.

2. Location Installed in mechanical area of basement and ducted to the exterior

3. Design Rate (CFM) 78

4. Frequency and 

Duration of Each 

Ventilation Cycle

The ERV has a 3-position switch: OFF; CONT (continuous): 

operates at low-speed (half the flow of high-speed); INTER 

(intermittent) operates at high-speed. The ERV is rated at a nominal 

150 CFM.

The ERV was balanced and adjusted to run at 80 CFM continuously 

low-speed, 160 CFM intermittently high speed. The 3-position switch 

on the side of the ERV is easily accessible. The original design 

specified a control to optimize the air delivery schedule to make 

efficient use of normal HVAC run times to ensure adequate 

ventilation each hour. That control was not compatible with the heat 

pump system’s 2-wire communicating control wiring.

* Minimum continuous rate in accordance with ASHRAE Standard 62.2-2010, Equation 4.1a: rate = 0.01*CFA + 

7.5*(Nbr+1), or Table 4.1a (see also 2012 IRC Table M1507.3.3 (1)).

The equipment and duct layout design criteria for all mechanical ventilation systems are shown 

in Table 6. The duct layout details illustrate a method to design an effective duct layout; the 

systems will be field verified and tested to evaluate the design approach.
20

Table 6. Mechanical Ventilation Design Data

Step Design Data Half Bath Hall Bath Master 

Bath Kitchen ERV

1 Design airflow

(CFM) 50 50 80 100 min. 150 high75 low

2

Manufacturer Broan Broan Broan Broan Honeywell

Model QTXE050 QTXE050 QTXE080 QDE30SS VNT5150E1000

ENERGY STAR®

rated Yes Yes Yes Yes Yes

CFM @ 0.1 iwc 50 50 80 0-280 150 @ 0.4 iwc

CFM @ 0.25 iwc 39 39 55

Sone @0.1 iwc 0.3 0.3 0.3 0.8-5.5

Watts @ 0.1 iwc 19.7 19.7 23.3

Duct fitting (in) 6 6 / 4 6 3.25*10

Specify control Timer Timer Timer Variable Honeywell 8150

3 Termination hood 

location

N soffit/

S soffit

N soffit/

E gable N soffit Roof/W gable E wall

4

Duct construction Metal Metal Metal Metal Metal/flex

Duct sealing Mastic Mastic Mastic Mastic Mastic

Duct insulation R-8 R-8 R-8 None R-8 as required

Duct length (ft) 30/3 20/3 15/7 12/12 32 in; 44 out

Duct elbows (qty) 3/1 at soffit 2 / 1 2/1 at soffit 2/2 2 in; 4 out

5 Total equivalent 

length (TEL) 120/53 90/53 85 / 57 82 256

6 Friction rate (FR) 0.08/.19 0.11/0.19 0.12 / 0.18 0.13 0.16

7 Minimum duct (in) 5/4 5/4 6/5 3.25*10 

(100 CFM) 6

8 Design duct (in.) 6/6 6/4 6/6 3.25*10 6

Note: values shown using #/# indicate the as-designed/as-built values.

Step 1: Determine the design airflow based on code requirements and industry best practices (e.g., ASHRAE Standard 

62.2-2010; Home Ventilating Institute recommendations: www.hvi.org/) 

Step 2: Select the fan and control

Step 3: Determine the termination hood location to minimize linear feet of duct and number of elbows

Step 4: Specify the duct construction details. Estimate the layout based on plans. Air sealing is required. Insulation is 

recommended to minimize condensation. Insulation is generally required for fresh air and stale air ducts that terminate 

outdoors for balanced (e.g., ERV or heat recovery ventilator) and supply-type whole-house ventilation. 

Step 5: Calculate the TEL, in feet. Example: 30 linear ft of metal duct + 2 elbows at 20 equivalent length (EL, in feet) + 

1 termination hood at 30 EL = 100 TEL 

Step 6: Calculate the design FR, in iwc. FR = ASP*100/TEL, where ASP is the available static pressure (iwc) of the fan 

at the rated airflow (from the manufacturer’s product data). Example: A bath exhaust fan rated 80 CFM @ 0.1 iwc, and a 

duct layout of 100 TEL: FR = 0.1*100/100 = 0.10 

Step 7: Determine the minimum duct size: using a duct calculator set fan airflow to friction rate and read the required 

duct diameter, rounding up to the next nominal size diameter or rectangular dimensions.

Note: Fitting equivalent length (EL is conditional upon pressure drip and friction rate (FR), and pressure drop depends 

on, among other factors, velocity. EL is commonly rated at 900 feet per minute (FPM); all else the same, a lower velocity 

reduces the effective length and increases the calculated FR. At 600 FPM, EL is reduced by approximately 50%, and by 

about 2/3 at 500 FPM (Figure A3-2, ACCA Manual D, Third Edition). The FR may be recalculated using this iterative 

approach as needed. 

Step 8: Specify the design duct size – may be increased to match the fan fitting, but if the duct size is larger than the than 

the fan fitting install a reducer fitting as close to the fan as practical.
21

2.6 Plumbing

The domestic hot water system design includes solar thermal collectors to preheat water for 

storage. In Green Home 1 and Green Home 2, the solar hot water storage tank fed into an electric 

on-demand auxiliary water heater. An alternative system was sought for Green Home 3, because 

of the cost of the electric demand backup system, which requires four 30-Amp circuits and a 

demand heater unit for a heater that is sufficiently large to supply all of the hot water under 

worst-case scenarios.

To reduce first cost and ensure acceptable performance for the owner, the team selected a more 

conventional, indirect solar preheat system with evacuated tube collectors heating an antifreeze 

solution that, in turn, heats water in a storage tank. Backup water heating is accomplished by an 

electric resistance element in the storage tank.

The energy savings for the SDHW system were estimated by software simulations (BEoptE+ 

v1.4) and through the solar rating analysis provided by the Solar Rating and Certification 

Corporation (SRCC).4 When rated as a system5 by SRCC, the solar thermal system uses a 

standard set of assumptions for the equipment including pumps, solar radiation, hot water use, 

hot water delivery temperature, and backup energy (either gas or electric). The system is rated by 

two metrics, solar energy factor (SEF)6 and solar fraction (SF).

Using SRCC methodology, SEF is calculated using equation 1.

SEF = Qdel

Qaux + Qpar

(1); where:

Qdel = Energy delivered to the hot water load. Using the SRCC rating conditions, this 

value is 41,045 Btu/d.

Qaux = Daily amount of energy used by the auxiliary water heater or backup element 

with the solar system operating.

Qpar = Parasitic energy used to power pumps, controllers, shutters, trackers, or any other 

equipment needed to operate the SDHW system.

SEF generally represents the comparison of the SDHW system to a standard water heater. Where 

a standard water heater would be rated with an energy factor (EF) that includes the efficiency of 

the water heater and storage tank losses, similarly the SEF represents these same parameters as 

well as the contribution of the solar. An alternative representation of the contribution of the solar 

hot water supply to the domestic water heating energy is the solar fraction (SF) which generally 

represents the portion of the water heating energy expected to be supplied, on an annual average, 

by the solar system. The SF is related to the SEF as shown in equation 2.

 4 Refer to www.solar-rating.org for information on collector and system ratings for solar hot water systems. 5 SDHW systems can be rated to the SRCC Standard OG300, Minimum Standards for Certifying Solar Water 

Heating Systems, June 2012, SRCC, Cocoa, Fl.

6 Refer to http://www.solar-rating.org/facts/system_ratings.html#RATING for a general discussion of the use of the 

SEF and SF in solar hot water system efficiency ratings.
22

SF = 1 − EF

SEF (2); where:

EF is a standard unit of backup tank energy efficiency, 0.9 for electric tanks, and 0.6 for gas 

tanks. Both the SEF and the SF are reported through the SRCC for specific system designs. 

Certification reports are issued on the system performance for selected climates (by city). 

Appendix B shows the report for two different system configurations.

Energy use estimates, however, from the simulation software used for whole-house energy 

analysis are somewhat limited. The simulation software uses a standard protocol to estimate hot 

water use, incoming cold water temperature by climate, and demand profile for hot water use. 

The simulation software assumes a standard flat plate solar collector with a standard electric tank 

element for backup. The simulation software allows the orientation of the solar collectors to be 

matched to actual installation conditions; solar radiation estimates are based on 30-year average 

weather data for any given location. A summary of the simulation results for the estimated hot 

water energy supply and use and the ratings for the collector system from the SRCC are shown 

in Table 7.

Table 7. Summary of Annual Hot Water System Energy Supply and Use

Parameter Value Unit

Delivered Hot Water Energya 8,992,976 Btu

Electric Inputb 5,163,840 Btu

Solar Heating Input 4,003,665 Btu

Total Input Hot Water Energy 9,167,506 Btu

SEF (calculated) 1.74

SF (calculated) 0.48

SEF (SRCC)c 1.70/2.10

SF (SRCC)c 0.46/0.57

Hot Water Energy Use, Standard 80-gal Tankd 3,028 kWh

Hot Water Energy Savings (Simulation) 1,515 kWh

Estimated Hot Water Savings Based on Actual System 1,773 kWh a Delivered energy is the domestic hot water supply from the tank for all uses in the home, based on 

simulations.

b Assumed to include all electrical inputs to the SDHW system. c The first value is for a standard system similar to the simulation model, the second value is for the 

installed system

d Without solar preheat system

The whole-house energy simulation software provides only limited solar hot water components 

and was not able to simulate the exact components installed at the NCTH. Based on the 

simulations, a calculated SEF was close to SRCC-rated SEF for the system components which 

were simulated. However, the actual installed system components had a rated SEF of 2.1. There 

was not a way to compare simulation results with SRCC rating for the specific system installed 

at the NCTH. A correction factor, based on the ratio of the simulated results to the SRCC rating, 

was used to raise the simulated performance of the solar system to more closely match the actual 

installed solar water heating components.
23

Because the domestic hot water system operates mostly independently from other building 

components, a cost analysis can be performed for this system independent of the whole house. 

Energy cost savings for the solar preheat system is approximately $225 annually. The contractor 

estimate for the installed system was about $8,300 net of a standard 80-gallon water heater. At 

this cost, the simple payback is more than 35 years and the financed cost is about twice that of 

the savings. Without some incentive program to offset the installed costs, or an alternative 

system offering lower costs, there is little financial benefit to the solar water heating investment. 

Furthermore, this simplified cost analysis does not include any maintenance costs for the solar 

system.

One potential alternative to solar water heating at the NCTH is a heat pump water heater 

(HPWH). Simulation results of an HPWH are summarized in Table 8.

Table 8. Annual Estimates for Water Heating System Options

Parameter Standard Electric 

Resistance Tank SDHW HPWH

Hot Water Energy Use, kWh 3028 1513 1503

Heating and Cooling Energy Use, kWh 3518 3497 3700

Total Heating, Cooling, Water Heating, kWh 6546 5010 5203

Net Energy Savings Over Standard – 23% 21%

Heating and Cooling Energy Savings (Increase) – 1% (5%)*

Standard – 80-gal electric tank 

* An HPWH draws its energy from the surrounding air. During cooling, it improves cooling efficiency. During 

heating, it increases the heating load. In a cold climate the net effect is typically an increased annual space 

conditioned energy use.

In this analysis, an HPWH uses approximately the same amount of energy as does the solar 

preheat system. Because an HPHW draws its energy from the surrounding air and the system is 

located in conditioned space, the energy penalty in this climate is an increase in heating energy. 

There is a very slight decrease in cooling costs in the summer months. Results are design 

estimates.

Based on an estimate of the installed cost for the HPWH of $2,781 and an annual energy savings 

of $171 (electricity at $0.127/kWh), the simple payback is almost 18 years, longer than the 

warranty and normal life expectancy for the appliance. As with the solar thermal system, state, 

utility, and/or federal incentives may reduce the installed cost by as much as 50% and, hence, 

could make this option cost effective to the owner.

2.7 Electric

For ICF construction, selecting the method to rough-in the electric is an important early-on 

decision. Different methods to install the electric wiring in ICF walls were debated during the 

design phase. One option was to have a final electrical design layout and install conduit for the 

wiring within the walls prior to pouring concrete. A second option was to pour the walls first, 

then cut the insulation on the interior to run the wires (commonly using a hot-knife), and foam 

over the wires. While the second method eliminates a minimal amount of insulation, it allows for 

more flexibility during installation and does not require a complete electrical plan and electrical 

work before concrete. The team decided on the second option as the most practical approach.
24

2.8 Lighting and Appliances

The team specified high efficiency lighting and appliances to maximize end-use energy 

efficiency for which the occupants are mostly in control. High efficiency lighting was increased 

to 100% using compact fluorescent lamps (CFLs) or fixtures or light-emitting diode (LED)

products. Controls (e.g., dimming) and appropriate lighting efficacy (e.g., light levels on surfaces 

or use of lamps) throughout the house will maximize efficiency and allow multiple lighting 

options. Additionally, some lighting fixtures commonly installed on the ceiling (e.g., hall light) 

were specified to be installed on the walls to minimize ceiling penetrations. Builder supplied 

appliances were specified to be ENERGY STAR.
25

3 Final Energy Solution Package Analysis

3.1 Energy Simulation Estimates

Using BEoptE+ v2.1 software,

7 an energy use optimization was performed to determine the least 

cost approach to achieve the greatest energy savings. Options for use in the simulations included 

various wood frame wall systems, exterior insulation options, infiltration levels, heat pump 

system efficiencies, and water heating system options, including solar hot water heating. The 

options were selected to demonstrate primarily the building envelope and mechanical system 

opportunities to achieve energy savings at the least cost. Cost estimates were all based on the 

NREL National Residential Efficiency Measures Database.8 Figure 13 shows the graphical 

results of the optimization.

Figure 13. Energy cost optimization simulation results

The optimization results differ from the maximum savings to the highest energy savings that still 

show an annualized savings (approximately 46% over the Building America benchmark with 

high performance) by the use of foam insulation in the wall cavity and an addition of a solar 

water heating system. These results compare well with the selected 44% savings features used in 

the NCTH.

The final energy efficiency solution package represented months of development by Home 

Innovation, LCCTC staff, trade contractor professionals, manufacturers, and product suppliers. 

The design process involved technical input, energy modeling, and optimization by Home 

Innovation and input on costs and other practical factors by team members. The set of features 

selected based on the design analysis included:

 7 A newer version of BEopt software was used to perform final simulation results than was available at the time of 

the initial analysis.

8 www.nrel.gov/ap/retrofits/
26

• Walls: ICF below-grade and above-grade, R-22 rated assembly

• Attic: vented, R-49 blown cellulose ceiling insulation, standard truss roof framing

• Windows: wood clad low-e, U-0.30, SHGC-0.28

• Air sealing: target and modeled 1.5 ACH50 

• Heating and cooling: ducts in conditioned space, ASHP, 2-stage, 16 SEER, 9.8HSPF

• Mechanical ventilation: ERV

• Appliances and Lighting: ENERGY STAR; 100% high efficacy CFL or LED

• Hot water: SDHW (SEF of 2.0)

The energy simulations, originally using BEopt v1.1, were updated using BEoptE+ v1.4, and 

most recently using BEoptE+v2.1 (Figure 14), which charts annual source energy savings9 of the 

house as designed versus the Building America Benchmark, shows a 44% reduction in the 

estimated energy use of the NCTH.10 Table 9 provides the numerical results and percentage 

change from the Building America Benchmark.

Table 9. Simulation Source Energy Summary

End Use Source Energy, MBtu NCTH Percent 

Savings

End Use Percent of Total

Benchmark NCTH Benchmark NCTH

Miscellaneous 39.89 28.54 28% 19% 24%

Ventilation Fan 1.94 3.02 –56% 1% 3%

Large Appliance 25.98 20.16 22% 12% 17%

Lighting 23.43 15.19 35% 11% 13%

HVAC Blower 11.86 1.41 88% 6% 1%

Cooling 5.42 3.55 35% 3% 3%

Heating 60.93 33.48 45% 29% 28%

Hot Water 40.61 12.61 69% 19% 11%

Total 210.06 117.96 44% 100% 100%

 9 Source energy represents the energy at the point of generation rather than at the house meter. 10 The Building America Benchmark analysis using the House Simulation Protocols has gone through a series of 

revisions. The latest revision (released December 2013) allows for the reference house to use an electric heat pump 

when natural gas is not available at the site and has been implemented in this analysis.
27

Figure 14. Simulation source energy results

3.2 Energy Efficiency Cost Analysis

The Research Center completed an in house cost analysis during the design process which 

provided the team with information for system selection (e.g., wall type). This analysis 

considered energy savings, occupant comfort, and synergistic cost containment benefits such as 

reduced material and labor costs. Original cost assumptions were refined and updated during the 

process, and are summarized in Table 10.

Home Innovation worked with LCCTC to understand incremental costs and finalize the cost 

analysis. Based on the estimated cost for the upgrades and the stated financing parameters, there 

will be on average an annual cost penalty of about $164 with the investment in the energy 

upgrades. Simple payback is about 18 years and the simple return on investment is about 6%. 

The high cost of the SDHW is one feature that may be optimized in lieu of other efficient water 

heating technologies.

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

Benchmark (HP) LCCTC-GH3

End Use Source Energy, Annual MMBtu

Hot Water

Heating

Cooling

HVAC Blower

Lighting

Large Appliance

Ventilation Fan

Miscellaneous
28

Table 10. LCCTC Green Home 3 Revised Cost Analysis

Design 

Feature Construction Category NCTH Design Specification Standard Feature Cost Premiuma

Foundation

Construction ICF system Poured concrete

Insulation, total value R-22 R-13, frame $2,528

Slab insulation Integrated with wall none

Above-Grade 

Walls

Construction ICF, 6-in. concrete core 2×4, R-13, R-5 ext. $3,305

2×6, R-19, R-5 ext.b $2,158

Structural sheathing None Wood structural none

Insulation, nominal R-22 R-18/R-24 none

Exterior air barrier House wrap House wrap none

Exterior finish Vinyl/brick Vinyl/brick none

Attic Insulation R-49 cellulose R-38 fiberglass $746

Windows U-value/SHGC 0.30/0.28 0.35/0.35 $124

Air Sealing Infiltration ACH50 1.5 ACH50 (target) < 7ACH50 $380

Heating and 

Cooling 

Equipment

Heating ASHP 2-stage

16 SEER/9.8 HSPF

1-stage ASHP

13 SEER/7.7 HSPFb $1,625

80% furnace/

13 SEER AC $1,025

HVAC Duct

In conditioned space 100% 100% none

Return duct Simplified, central Standard, central –$300 Return air pathway BR transfer grilles Door undercut

Spot 

Ventilation

Bath exhaust fan (no.) ENERGY STAR Standard $120

Kitchen exhaust fan Vented outdoors Vented outdoors $0

Whole-House 

Ventilation Mechanical control ERV with control

Bath fan/timer $1,560

Return air

duct/damper

auto. controllerb

$1,355

Domestic 

Water 

Heating

Water heater SDHW Standard electric

$8,309 Capacity 80 gal 80 gal

Fuel Electric element Electric element

Tank EF 0.95 0.91

Plumbing Fixtures Low flow Standard $40

Lighting CFL lamps/fixtures 100% 50% $41

ENERGY 

STAR 

Appliances

Dishwasher, refrigerator, 

clothes washer

Dishwasher, refrigerator, 

clothes washer

Standard $470

Total Cost Premium Over Standardc $18,348

Annual Mortgage Premium at 5% Interest and 30 Years $1,182

Annual Utility Cost Savings $1,018 a Cost premium over standard construction feature (local standard or LCCTC standard)

b Used for comparison purposes only, not used in the cost analysis c Premium over standard construction elements and gas furnace
29

4 Test Results

The test plan for this NCTH outlined the technical approach for this project. Test results are 

summarized below (Table 11).

Table 11. Home Innovation Test Results

Test Measurement Result

House Leakage, 

Intermediatea

1220 CFM50 1.59 ACH50

House Leakage, Finala 843 CFM50 1.10 ACH50

Duct Leakage, Intermediateb Not measured

Duct Leakage, Totalb 239 CFM25 5 CFM25/100 ft2 cfa

Duct Leakage, Outdoorsc 0 0

EF: Powder Roomd 67 CFM Exceeds 50 CFM rating

EF: Hall Bathd 127 CFM Exceeds 50 CFM rating

EF: Master Bathd 91 CFM Exceeds 80 CFM rating

EF: Kitchen Range Not measured

ERVd 90 CFM low-speed Exceeds 75 CFM rating a Depressurization test to 50 Pa using Minneapolis Model 3 blower door and DG700 manometer

b Pressurization test to 25 Pa using Minneapolis Series B duct blaster and DG700 manometer

c Pressurize house to 25 Pa, then pressurize duct system until the difference between the house and duct system is 

zero, using above equipment. 

d Measured using Alnor 6200 flow hood 

The intermediate blower door test was performed after drywall and extensive air sealing from the 

attic, but before attic insulation. The only noticeable leakage was through the top plate at the 

laundry room plumbing and through the master bath exhaust fan. These areas were sealed again 

before insulation. The final blower door test was a notable 1.10 ACH50. 

Due to the students’ schedules, the duct system in the basement was not completed until after 

drywall. This unusual sequence precluded a planned intermediate duct test. During final testing, 

total duct leakage was higher than expected, but duct leakage to outdoors was zero as expected. 

Air balance testing, described below, indicates that the majority of leakage is in the air handler 

cabinet and return ducts. 

All mechanical ventilation ducts were inspected before attic insulation to confirm duct sealing, 

insulation, and geometry. The measured bath EF airflow rates exceed the nominal ratings and fall 

along the manufacturer’s fan curve for lower static pressure (except the hall bath), indicating a 

properly designed duct layout. The measured airflow of the hall bath far exceeds design and fan 

curve data, and indicates a larger capacity fan was installed. The kitchen EF could not be 

measured at the range hood or termination hood using a standard flow hood, and that duct was 

not easily accessible in the attic to use a hot-wire anemometer. 

The ERV low-speed operation was originally measured at 90 CFM, but reduced to 80 CFM (this 

ERV has a built-in procedure to adjust motor speeds for airflow and balance). The method to 

install the stale air exhaust in the living area low on a wall using a standard return duct boot and 

grille made measuring the airflow using a flow hood a simple matter. The team decided that the 
30

ERV should run continuously at low speed, and the ERV was balanced, to provide a slight 

positive house pressure, with the air handler off because this condition represents the majority of 

hours per year. When the air handler operates, the fresh airflow rate will be somewhat higher due 

to the air handler fan (the stale exhaust airflow rate is more of a constant because that is ducted 

independently of the distribution duct system). The team considered this the best compromise, 

because balancing with the air handler operating would have led to a somewhat lower fresh air 

rate the majority of the time. 

The heating and cooling air distribution system was balanced and tested. The dip-switches in the 

air handler were selected so that the electronically commutated motor drive would provide a 

nominal 1040/700 (high-stage/low-stage) CFM. Actual high-stage airflow was measured at 1100 

CFM using a flow-grid. The supply branch ducts required balancing to be within the 25 

CFM/20% ENERGY STAR limit. Measured airflows at all supply registers and return grilles 

indicated that the majority of duct leakage was due to the air handler cabinet or return ducts or a 

combination of both. The bedroom transfer grilles provided pressure balance for these rooms 

within the 3 Pa ENERGY STAR limit. The accuracy of the airflow measurements at the 

basement registers and grilles is somewhat questionable; the registers and grilles located at the 

ceiling height of the unfinished basement did not have drywall to place the flow hood against. 

However, testing was conducted in the cooling mode and supply registers were closed, and the 

measurements appeared reasonable. 

There are no combustion appliances with the potential to back-draft, but the effect of exhaust fan 

operation on house depressurization was measured for research purposes. The adjusted house 

depressurization was 8 Pa with the three bath exhaust fans operating, 12 Pa with all bath fans and 

the kitchen exhaust on low, and 17 Pa with all bath fans and kitchen fan on high. 

HVAC commissioning was considered an important component of final testing. A factory 

technical representative was on site to verify that all equipment was installed and operating 

within manufacturer specifications. This step was helpful to complete all startup forms and 

served as a valuable educational component. 

The domestic hot water pipe volumes were measured. The volume of the PEX manifold and pipe 

from the water heater was estimated at 28 ounces. The farthest fixture, by volume, the 1⁄2-in.

branch run to the hall bath, added approximately 55 ounces, for a total of 83 ounces. Actual flow 

was measured using a calibrated bucket and thermometer to measure the water temperature rise. 

Even with a “hot” manifold, this test method required more than 64 ounces of water to produce a 

10°F temperature rise. This result may be due in part to the rotary shower valve that allowed a 

relatively large volume of cold water when initiated; sinks with standard faucets appeared to 

provide results more in line with expectations. 
31

5 Discussion

5.1 U.S. Department of Energy Challenge Home Certification

The NCTH earned certification by the DOE Challenge Home Program. The mandatory 

requirements (DOE 2013) are summarized below (Table 12).

Table 12. DOE Challenge Home Mandatory Requirements

Area of Improvement Mandatory Requirements (summarized) NCTH

1. ENERGY STAR Certified under ENERGY STAR Qualified Homes 

Version 3 Met

2. Envelope

Fenestration shall meet ENERGY STAR

requirements.

Ceiling, wall, floor, and slab insulation shall meet 

2012 IECC levels

Met

3. Duct System Within the thermal and air barrier boundary Met

4. Water Efficiency Hot water delivery systems shall meet efficient 

design requirements Exempt

5. Lighting and

Appliances

Installed refrigerators, dishwashers, clothes washers 

are ENERGY STAR qualified

80% of lighting fixtures are ENERGY STAR

qualified

Bath ventilation fans are ENERGY STAR qualified

Met

6. Indoor Air Quality U.S. Environmental Protection Agency

Indoor airPLUS checklist Met

7. Renewable Ready Solar electric checklist

Solar thermal checklist Met

The NCTH meets all other DOE Challenge Home certification requirements except for hot water 

delivery. The PEX manifold distribution was carefully designed to minimize tubing diameter and 

length, but the two largest volume runs, both 1⁄2-in. serving tubs, exceed the 64-ounce limit by 

approximately 20 ounces. As of this writing, DOE is reviewing the hot water delivery 

requirement for the time-temperature profile for hot water fixtures, and is not enforcing the 

original requirement at this time. The NCTH Home Energy Rating System Index is 45 

(ENERGY STAR Target Index is 60; DOE Challenge Home Target Index is 52).

5.2 Insulated Concrete Form Wall Implementation

The footer was formed using a product that integrates the form and perimeter drainage on the 

interior and exterior and left in place after the concrete is poured (Form-a-drain). A self-adhesive 

capillary break was installed over the footer. The ICF walls were formed and poured one level at 

a time. The upstairs walls were constructed directly on the foundation walls, creating a 

monolithic wall, without framed rim areas, from the footer to the top of the first floor ceiling. A 

peel and stick water proofing membrane was installed over the footing and 3 ft up the foundation 

wall, and dimpled water proofing membrane was installed from footer to grade and flashed, to 

protect the foundation from groundwater. A metal termite shield was let into the EPS, but the 

continuous exterior foam could be a termite issue in specific mixed-humid climates. 
32

Pressure-treated wood bucks for windows and doors were installed before concrete. At the top of 

the ICF wall, a treated wood top plate supports high-heel trusses installed 24 in. on center. The 2-

in. × 12-in. bucks and top plates were rip-cut to 11 in. to cover the entire width of the ICF wall 

without interfering with interior or exterior finishes. Laminated veneer lumber ledger boards 

were anchored to imbedded steel connectors to support hangars for the 14-in. open web floor 

truss joists 24-in. on center (Figure 15).

Figure 15. Floor framing

House wrap, not required by the ICF manufacturer, was installed above grade to help control 

water entry. Water does not generally affect the foam or concrete but could adversely affect 

interior finishes. The house wrap also protected the EPS foam from ultraviolet radiation during 

the summer construction break between academic years (the schedule allowed roof and window 

installation but not siding before summer break) (Figure 16). Windows and doors were installed 

after house wrap and flashed using ice and water barriers and butyl flashing tape (Figure 17). 

Doors were ordered with full depth exterior casings, but arrived with short door-steps that had to 

be modified in the field (Figure 18). The windows were flanged. Their standard depth casing 

required finish casings on the interior. After summer break, vinyl siding and a limited amount of 

brick veneer were installed.

Figure 16. House wrap installed before

summer break Figure 17. Window flashing
33

Figure 18. Door step details

The ICF manufacturer provided training to install the electric within exterior walls. Interior foam 

was cut using a hot-knife to rough-in the electrical boxes and wiring. The majority of wiring was 

installed horizontally within the floor framing and then vertically as required to minimize 

horizontal wiring runs through the foam. Installing the wire behind the ledger board was tricky at 

first but proceeded smoothly after the first few. Cutouts in the foam were sealed using spray 

foam (Figure 19). 

Drywall was installed directly on the ICF walls. The basement was not finished, but drywall 

provided a thermal barrier over the EPS foam (Figure 20).

Figure 19. Foam over rough wiring at ICF Figure 20. Basement drywall

5.3 Air Sealing and Insulation

The framed portion of exterior walls represented a relatively small area, but required a relatively 

large effort to air seal and insulate compared to the ICF walls. For the fireplace bump-out, the 

2 × 6 wall cavity was sealed at the sheathing, and the bottom plate was sealed at the deck. Next, 
34

the wall cavity and ceiling area behind the fireplace were netted and blown with cellulose 

insulation (Figure 21). Drywall was installed before the direct vent fireplace unit. The 

cantilevered floor was sealed and insulated from below. The living room cathedral ceiling 

exterior gable was sealed at the sheathing, and then netted and blown with cellulose the full 

11-in. depth of the ICF (Figure 22 and Figure 23). Similarly, the opposing knee wall gable at the 

vented attic was sealed and installed in this same fashion after a rigid foam air barrier was 

installed (Figure 24 and Figure 25).

Figure 21. Fireplace bump-out

Figure 22. Framed gable 

before air sealing and

insulation

Figure 23. Framed gable after 

air sealing and insulation

Figure 24. Knee wall air barrier
35

Figure 25. Knee wall insulation

Penetrations, rough openings for windows and doors, and the truss bearing plates at the top of the 

ICF walls were sealed in a conventional manner using canned spray foam. One student sealed the 

ceiling plane at all top plates (Figure 26), penetrations, and air barrier at the top of the HVAC 

duct chase (Figure 27) using canned spray foam. This approach to seal the ceiling plane from the 

attic allowed for inspection, testing, and remediation before attic insulation. For the tray ceiling 

in the dining room, drywall was installed at the ceiling, and sides, and sealed before the tray 

framing, so no additional air sealing was required from the attic for this detail. An insulation dam 

was built at the attic access to prevent the blown R-49 attic insulation from spilling (Figure 28).

Figure 26. Sealed top plate

Figure 27. Sealed air barrier

at the HVAC duct chase

Figure 28. Insulation dam

at attic access

5.4 Hot Water

The hot water system components are shown in Figure 29. The solar hot water tank has an 

integral heating element for backup heating to the solar supply. The PEX manifold water 

distribution system includes potable water delivery as well as filtered rain water delivery to the 

outdoor spigots, toilets, and clothes washer.
36

Figure 29. Solar hot water storage tank and PEX piping manifold

5.5 Lighting

The students designed and installed an impressive combination of LED ambient, task, and accent 

lighting in the kitchen (Figure 30). Wall sconces in the hall in lieu of standard ceiling fixtures 

helped to minimize ceiling penetrations. All lighting was LED or CFL fixtures or bulbs.

Figure 30. High efficacy lighting in the kitchen

5.6 Heating and Cooling Design

The heating and cooling duct distribution design operates very quietly during high-speed air 

handler operation, and provides good air mixing and even temperatures throughout the house 

based on a number of measurements during four visits during the cooling season. During one 
37

visit, relative humidity in the basement was 60%. This measurement was made (during a humid 

period when the doors were mostly open due to ongoing construction), and a dehumidifier was 

installed temporarily to control humidity. As mentioned, the 3-ton, 2-stage heat pump was sized 

to satisfy cooling in low-stage; a 2-ton, 2-stage system would dehumidify better, but the tradeoff 

was improved heating capacity for this climate. Potentially, higher humidity could be the result 

of concrete curing within the walls or the recently poured basement floor. 

5.7 Mechanical Ventilation Design

The measured airflows of the bath exhaust fans exceeded nominal ratings because all had a low 

resistance duct layout (even fewer linear feet and elbows than designed for) (Figure 31). 

Ventilation ducts were rigid metal, larger diameter than standard, sealed with mastic, and 

insulated to prevent condensation. Two of the fans terminated at a low pressure drop soffit hood 

(Figure 32). The third, and the kitchen range exhaust, terminated at a gable wall.

Figure 31. Short and direct bath

exhaust fan duct

Figure 32. Bath exhaust duct

termination at soffit

The original plan was to regulate the ERV, operating intermittently on high speed, using a 

control to take advantage of air handler run times when possible. The heat pump system 

including the thermostat used a proprietary two-wire communication system that was not 

compatible with that control, so instead the ERV provides adequate ventilation rates running 

continuously on low-speed. This appears to be a better solution based on air handler run time, 

particularly during the moderate swing-season. The dedicated 7-in. oval stale-air duct from the 

living room (Figure 33) was initially somewhat noisy, objectionable because the air handler 

could not be heard at all. The duct between the grille boot and the ERV was reworked to 

minimize turbulence, and this eliminated all ERV system noise. This partially integrated duct 

layout allows for simple airflow measurement using a flow hood.
38

Figure 33. Dedicated “stale” air duct in living room
39

6 Conclusions

6.1 Research Questions

The high performance features of the NCTH were evaluated for energy savings, performance, 

and cost effectiveness. The design evaluation was used to develop a more cost effective approach 

to develop solution packages that could apply to CZs 4 and 5. The answers to the research 

questions from Section 1.4 are presented below.

1. How does the ICF wall system compare with the builder’s standard high performance 

foundation and framed wall systems in terms of estimated energy use?

The design analysis demonstrated that an ICF wall system is a cost-effective option for the 

climate. When compared with walls of similar insulation, ICF construction is predicted to use 

less energy. Additionally: 

• The ICF foundation wall is predicted to use less energy and estimated to cost at least 

neutral to a similarly insulated foundation wall. This is considered a “high-R” foundation 

wall.

• The ICF above-grade wall is predicted to use about the same energy and estimated to cost 

more to install. This is not considered a “high-R” above-grade wall in this climate.

• Installing additional rigid foam on the ICF walls would be a simple method to increase 

wall R-value as needed or desired. 

• The high level of thermal mass is expected to reduce temperature swings within the 

rooms and cause the ASHP to operate in low-stage for longer periods, resulting in more 

even temperatures throughout the house and improved occupant comfort.

• Air sealing is simplified with ICF wall construction, and allows air sealing efforts to be 

focused on other critical areas such as the ceiling plane (see research question 2).

2. How is the air sealing strategy different for ICF construction?

The ICF wall system resulted in a notably low whole-house infiltration rate at a cost that is no 

more than air sealing a standard home to modest infiltration levels. The air sealing strategy for 

ICF construction is somewhat simplified because of the inherently tight wall assembly. This 

feature increases the relative importance of air sealing at windows and doors, the interface 

between the roof trusses and the top plate of the wall, and at the ceiling plane. The limited 

framed exterior walls in the NCTH (fireplace bump-out and living room cathedral ceiling gable) 

required a relatively large air sealing effort with respect to the small area of wall, reinforcing the 

air sealing advantages of ICF construction. Use of conventional air sealing techniques that do not 

require specialized equipment was appropriate to obtain the very low infiltration rate.

3. What are the heating and cooling design, selection, and performance issues and solutions 

that emerge based on the high performance envelope design in CZ 5?

The heating and cooling system design issues centered on the selection of the fuel type for the 

heating system and the sizing of the equipment. Fuel selection was of particular interest because 

the builder did not wish to use a GSHP system due to cost and complexity, and natural gas was 
40

not available. Analysis showed that the high efficiency ASHP was much less expensive to 

operate than a propane gas furnace. A two-stage ASHP was selected to provide sufficient heating 

capacity, cooling effectiveness, and system response to the ICF walls (the much higher mass in 

the ICF wall influences heat transfer through the wall and affects how the heating and cooling 

system responds to changing outdoor conditions). DSHP systems were not considered because 

LCCTC considers installing a conventional duct distribution system an important educational 

aspect; DSHP systems offer higher efficiency ratings but hardware costs tend to be higher as 

well. This project will not be monitored, so the performance of the selected high efficiency, twostage heat pump system during the heating season will be evaluated based on feedback from 

LCCTC and the future home owner. An energy efficient ASHP can be the best heating and 

cooling solution for high performance, low-load homes in a cold climate, even where natural gas 

is available.

4. Are the proposed methods to ensure effective mechanical ventilation successful?

Yes, the measured airflows for the ERV and bath exhaust fans were well above the nominal 

capacities and therefore successfully met design expectations. The design approach identifies the 

duct design friction rate and minimum duct size, so rounding up to the next standard size duct 

should, and did, result in better than nominal rated performance. For this project, the as-built 

duct layouts for the bath exhaust fans were shorter than designed for (reduced total-effectivelength) and this contributed to the good results. The ERV as-built duct layout was the same as

the design, and the measured airflow verified the design method. This approach would benefit 

from additional termination hood pressure drop or equivalent length data from manufacturers or 

other industry organizations. 

The partially integrated duct layout for the ERV was also successful because it allowed for a 

simple, single-point airflow measurement using the flow hood, and did not require the air handler 

to operate to distribute fresh air (although distribution will be better when the air handler is 

operating). The best solution would be a dedicated duct layout for the ERV to operate 

independently, but this approach would add cost. 

A better method to measure kitchen range hood exhaust airflow is still needed. Using a flow 

hood to measure airflow at the termination hood from outdoors is not accurate (due to siding 

irregularities and wind) and may also require a ladder. Using a flow hood indoors would require 

a custom sleeve. A hot-wire anemometer could work in some situations but not others with 

limited access. For this project, the fan was rated at 300 CFM on high speed, so achieving the 

100 CFM minimum required airflow was not a concern. 

5. How do the theoretical domestic hot water system designs compare in terms of 

performance and cost?

The SDHW system provided the lowest estimated operating cost, but the installed cost was very 

high. LCCTC elected to use a SDHW system because a portion of the system was donated, 

continuity with the first two houses in the community, and for educational purposes, but based

on analysis SDHW is not considered cost-effective, even with federal or state subsidies. 

Similarly, the HPWH provided a low estimated operating cost but a relatively high installed cost 

compared to a conventional electric tank water heater. The HPWH is also not considered cost
41

effective unless subsidies are available. Propane gas alternatives were also not found to be cost 

effective given the high cost of propane in this market.

6. Are the elements of the energy efficiency package cost effective and market ready?

All selected components of the energy solution package for the NCTH are existing technologies 

that are market ready. 

Building with ICF walls requires some different skill sets, but these skills would be relatively 

straightforward to acquire and could be worthwhile for a builder interested in making this 

technology standard practice. ICF construction is deemed cost effective for foundation walls and 

when used for both foundation walls and above-grade walls. ICF construction may or may not be 

cost effective if used only for above-grade walls with respect to energy use, but may still be a 

good choice if other criteria such as sound attenuation and resistance to wind and fire are 

priorities. 

As mentioned above, the solar hot water system is not considered cost effective, and the ASHP is 

considered cost effective for heating and cooling. 

6.2 Key Findings and Lessons Learned

This research addresses the primary Building America goals to develop market-ready solutions 

that improve energy efficiency, durability, affordability, and comfort. Small and large builders 

can benefit from the analysis methods used in this report to evaluate and select energy solution 

components. 

ICF wall construction merits consideration as a practical, cost-effective, and energy-efficient 

alternative to conventional foundation walls and above grade walls for high performance homes 

in cold climates. For additional thermal insulation, select ICF blocks with thicker foam, or install 

additional rigid foam on the ICF walls. The sound attenuation and fire resistance properties may 

be particularly attractive in cities or other noisy environments (e.g., near an airport or train 

tracks) in all climates. 

Attention to air sealing details, in conjunction with ICF construction, resulted in a very tight 

building envelope at a low incremental cost. An intermediate house leakage test was performed 

before attic insulation and other interior finishes. This additional test allowed for a few leakage 

areas to be sealed again, a relatively simple and inexpensive process at this stage, and resulted in 

a significant improvement of the house leakage rate.

An energy efficient ASHP can be a cost-effective solution to heat and cool low-load homes in a 

cold climate. Annual energy costs for the high efficiency ASHP nearly equals that of high 

efficiency natural gas heating and is 30% less than that for high efficiency propane fuel heating, 

and at a lower installed cost. The two-stage heat pump for this project provides higher heating 

capacity in high-stage, and sufficient dehumidification and cooling in low-stage. Additionally, 

the two-stage system is well suited to respond to the expected thermal mass effects of the ICF 

walls. The ICF walls slow the heat loss from the house because the thermal mass reacts more 

slowly to changing outdoor conditions (thermal lag), and this effect will generally cause the heat 

pump system to run in lower speed but for a longer period of time.
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The importance of effective mechanical ventilation merits a careful duct layout, similar to those 

used for heating and cooling systems, to ensure measured ventilation airflows meet design 

expectations. The approach presented in this report could help HVAC designers and trade 

partners deliver the benefits of effective ventilation to builders and future occupants in any 

climate. 

Without incentives, SDHW systems may not be as cost effective as other water heating 

technologies.

The thermal enclosure, heating fuel, and domestic hot water analyses reinforce the concept that 

for optimum energy performance in a cold climate, investing more in the building enclosure can 

result in less investment required in the mechanical systems. 

Locally, this research project successfully demonstrated a higher energy performance level that 

is not common in this market. Students and faculty gained practical educational experience 

building with high performance methods and materials, so a knowledgeable workforce is 

accelerated into the market. The garage serves as a sales and educational showcase for this and 

previous Building America projects for prospective buyers and other interested parties in the 

community (Figure 34). Manufacturers and vendors are eager to participate in these high 

visibility projects.

Figure 34. ICF display in the garage (sales/education office) of the NCTH
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References

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ACCA (2006). Manual J: Residential Load Calculation. Eighth Edition. Arlington, VA: Air 

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ACCA (2009). Manual D: Residential Duct Systems. Third Edition. Arlington, VA: Air 

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ASHRAE (2010). ANSI/ASHRAE Standard 62.2-2010 Ventilation and Acceptable Indoor Air 

Quality in Low-Rise Residential Buildings. Atlanta, GA: American Society of Heating, 

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BSC (2009). High-R Wall Assembly-7: ICF Wall Construction. Enclosures that Work. 

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IECC. (2009). 2009 International Energy Conservation Code. Washington DC: International 

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Rudd, A. (2009). Top Ten Issues in Residential Ventilation Design. Building Science Insights 

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Smegal, J.; Straub, J. (2009). Building America Special Research Project: High-R Walls Case 

Study Analysis. Research Report – 0903. (Rev. 2011; 2012). Somerville, MA: Building Science 

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Somerville, MA: Building Science Corporation. 
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Appendix A: House Plans

LCCTC

Apprentice Green Community, Mount Joy, Pennsylvania 
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47
48

Appendix B: Solar Thermal System Rating
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50
51
 

DOE/GO-102014-4485 ▪ September 2014

buildingamerica.gov