Agreed. It is a lot cleaner too. I get headaches pretty quickly in a building that's heated by a torpedo heater and the moisture coming off of a ventless propane heater is something you don't want in a garage. It condenses easily on the ceiling insulation and inside walls if the place is not well insulated. Sooner or later that can lead to a serious mold issue.
I do hate to disagree with anybody having more than 10 times my number of posts...but I just don't buy the moisture issue on ventless heaters in a standard garage. And I use one nearly every other weekend in my garage.
For every cubic meter of natural gas (methane) we burn "ventless" we put just over 3lbs of water into the air through combustion. Or we say that for every 100,000 btu's of output you would get something closer to 9lbs of water. Let's call it a gallon for nice round numbers.
So for a "decent size" three stall garage of 825 square feet let's assume a nice average heat load, in the dead of winter, of 20,000 btu/hr to keep it at a cozy 75 degrees while working. In this case we'd have to be heating the garage for 5 hours to put a gallon of water into the air, approximately.
Further, let's say the above mentioned garage has an unheated relative humidity in the dead of winter of 80-85% if it holds at 55 degrees F. Dim's on this garage are 25x33 with 10' ceilings. This garage holds 8,250 cubic feet of air. In an unheated state it holds about a half gallon of water in the above referenced temp/RH. In this case, assuming 20,000 btu heat requirement, we'd be adding roughly 0.2 gallons of water each hour we run the heater. Does this represent a 40% increase in "humidity" every hour we're running the heater (.5 gallons to .7 gallons)? Not even close. At 75 degrees air holds more than twice as much water as it does at 55 degrees.
If we add 0.2 gallons but we also raise the temp to 75 degrees we end up with an increase in relative humidy of 2% or 3%. How many hours can we continue this without exceeding the water capacity of the air and we end up with "condensation all over the place"? Anecdotally I can tell you I've run mine all day long (10+ hours) more than once without having any condensation on the ceilings, walls, tools or anywhere other than my cheapo garage window. I'm really not willing to do the math required to find a real answer for "how long can you go" but I suspect there certainly is a real limit at some point. Can you realistically reach that limit in a garage that leaks air all over the place (garage doors, attic, etc)? I have no idea.
I guess you could argue that condensation is more of a concern when the garage cools after you shut off the heater. This is when the excess moisture will want to leave the air. But garages leak air, we park wet cars in them all the time, etc and so on. I don't believe ventless heaters will cause any more of a moisture issue than parking a car packed with snow in the undercarriage inside, or washing a car for that matter. I don't know many people who park their cars outside in the winter to keep the snow from melting in the garage for fear of mold on the ceiling...
My two cents only....or three cents I suppose.
