The District’s Wood Burning Fireplaces And Wood Burning Heaters Rule (Rule 4901) is 

the most stringent rule in the nation and significantly reduces emissions of direct PM2.5 

emissions when and where those reductions are needed most, in urban residential 

areas during periods of atmospheric stagnation. The Rule collectively reduces 

emissions of 5.1 tons-PM2.5/day. Amendments to the rule also lowered the curtailment 

threshold for non-registered wood burning devices from 30 to 20 μg/m3, significantly 

lower than any other rule in the nation. The below discussion provides further 

clarification and summarizes information included in the staff report prepared during 

adoption of Rule 4901.

Registration of Certified Wood Burning Devices

Rule 4901 allows certified wood burning devices to be operated during days when the 

pollutant concentration levels are forecast between 20 μg/m3 and 65 μg/m3 as long as 

the device is registered with the District and operates in accordance with Rule 4901 as 

follows:

1. Wood burning devices must be inspected by a Qualified Wood Burning Heating 

Professional and receive a certification prior to receiving a registration from the 

District. 

2. Qualified Wood Burning Heater Professionals must meet the following

requirements:

a. Maintain a professional certification as outlined in Rule 4901.

b. Apply to the District and be placed on a list of approved Qualified Wood 

Burning Heater Professionals.

3. Qualified Wood Burning Heater Professionals are required to conduct a thorough 

and rigorous review and evaluation of the wood burning device before providing 

a certification to the District.

4. Once the Qualified Wood Burning Heater Professional completes the inspection 

and provides a certification for the device, the registration is issued with a set of 

operating conditions for compliance with Rule 4901. This includes requirements 

for the wood burning device to operate in compliance with Episodic Wood 

Burning Curtailments issued by the District and prevents burning of any 

prohibited fuel types as identified in Rule 4901. 

5. Registrations are valid for a period of up to three wood burning seasons from the 

date of registration issuance; however, certificates can be disqualified if the 

District finds the wood burning device is operated in violation of the requirements 

of Rule 4901.

6. Upon completion of the three-season period, the registration of the unit will need 

to be renewed and again pass an inspection by a Qualified Wood Burning Heater 

Professional. 

Due to the stringent requirements for registering a wood burning device, it is expected 

that a limited number of residents will take advantage of registering their wood burning 

devices. 
During the rule 4901 development process, the District performed a worst-casescenario analysis of estimating the potential increase in emissions from the transition of 

high-polluting uncontrolled devices to clean certified registered devices operating when 

pollutant concentration levels are forecast between 20 μg/m3 and 65 μg/m3 (Appendix 

B - Emission Reduction Analysis). In this analysis, the District assumed that 24% of all

existing high polluting wood burning devices in the Valley would transition to clean 

certified units, all 24% of devices would register these devices with the District, and all 

24% registered devices would operate on days when PM2.5 concentrations were

projected to be between 20 and 65 μg/m3. Based on this scenario, the District 

estimated a total increase in emissions of only 0.22 tons per day (tpd). 

The above mentioned scenario is based on a worst-case and unrealistic scenario. The 

assumption that all wood burning devices would transition to clean certified wood 

burning devices was solely to calculate the absolute worst case scenario. Through the 

District’s Burn Cleaner incentive program, over 80% of devices have been replaced with 

natural gas-fired units. This is indicative of the Valley-wide trend of the transition of high 

polluting devices to clean units. Furthermore, as discussed earlier, only a minority of 

EPA clean certified devices are expected to register due to the stringent registration 

requirements under Rule 4901. A more reasonable, but still conservative, assumption 

would have been to assume only 20% of the 0.22 tpd emissions would occur because 

of the aforementioned transitions (still assumes that all clean certified devices register 

with the District). Taking these more accurate factors into account and applying them to 

the previous highly conservative analysis results in a more representative emission 

increase of 0.044 tpd (0.22 tpd x 20% = 0.044 tpd) when air quality is forecast to be 

between 20 and 65 μg/m3. This amount is insignificant with respect to PM2.5 

concentrations and does not take into account the 3.33 tpd of direct PM2.5 emissions 

reductions from the lowering of the curtailment threshold, and the 2.04 tpd reductions 

from the transition to the cleaner certified units. 

The combination of stringent requirements that must be met to register a wood burning 

device, including all associated costs for receiving a registration, increased transition to 

natural gas-fired units instead of wood-fired units and the de minimis amount of 

emissions resulting from the few units that can be used when PM2.5 is forecast to be 

between 20 and 65 μg/m3 will result in an insignificant impact during this period and 

Rule 4901 as a whole results in significant emission reductions.