Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Descriptions lists unit weight as 55lbs, shipping weight is listed at 28.  How much does it weigh? And - does this unit have to be hung from the ceiling?
Document: I purchased a used unit and it looks like new. I have only given it a three star as i haven't had it installed yet. It looks good.
I thought I could get away with no venting on this based on descriptions but discussed this with a plumber and the consensus is, since I live in MinneSNOWta with all the snow melt off in the garage, with no venting there would be a ton of moisture from the snow melt with no where to go so if you buy it, don't forget to budget in the cost to vent!
Unless your building is very 'leaky', consideration for additional ventilation is needed and likely necessary. This does not add that much to the heater run time.These heaters and their associated thermostat (one came with a thermostat, the other did not - new units should have one) are powered by an built-in thermopile, a group of thermocouples that generate a 650 mV signal as long as the pilot is on.
A fan (or 2 - I'm putting in 2 ceiling fans) is a big help in getting the heat distributed throughout the building.Pros:  Easy installation, no external electric required, complete w/ thermostat (new units),no direct vent requiredCons:  Proper ventilation is required (common sense)
This keeps my 3 bay garage warm and toasty , Very easy to Install , no power needed for stat
This heater needs a shield for the pilot light. It has the right flame length per instructions but the slightest breeze blows it out. Needs to be relight each time it cycles off. Working with mfg for a fix.
Thermostats that use a 650 mV control are available, but many are set up to control larger furnaces and use 12/24V or even 120 V AC, so be careful if you need a new or replacement thermostat. One of my local home improvement stores carried a 650 mV thermostat (both had several as catalog items), but they both had a number of 12/24v DC and 120v AC thermostats in stock.
The heater didn't work when first installed.pilot light wouldn't stay lit. Talked with tech person &  he sent me a new thermocouples & gas valve. Found out it was a defective valve. Now the heater works great. Tech erson was great to work with.
Received timely and it's a great heater. Also, a part was missing and the instructions said to contact the manufacturer. They provided the missing part immediately. Installation relatively easy and instructions good.
Performs perfectly, thermostat controls the temperature at exact temperature and heat is evenly distributed. A good price for a great heater!
Answer: Not sure where the 55lb number came from. Definitely feels more like 28. They can be suspended by chain from the ceiling or you can make brackets out if angle iron to suspend from a wall. Good luck. Adam