#18
I am proposing to heat a oversize 3 car garage The purpose to keep the garage at say 40 degrees Only run it on really cold days and to keep the area warm under bathrooms and extra bedroom. It will be well insulated. I propose to use a Dayton run on 240 and 40 amp circuit. I am seeking advice. The line is basically ordered cost of gas line and heater unknown. Any advice is sure welcome! Thanks in advance for any opinions.
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#19
Since a heater is considered a continuous load by the electric code, you're using up to 32A at 240V, or 7.7kW. At my $0.10/kW-hr (marginal, after the initial minimum usage, but including energy, delivery, and taxes) that would be $0.77/hr. Most folks pay more than I do. Not cheap to run.

But gas isn't cheap to install, including the heater itself. Though gas is much cheaper usually than electric power.

In other words, I have no idea. It depends on how much it will run to maintain 40F. And how long the desired payback period in savings of gas over electric is.

It almost sounds like electric may be ok in this instance.
Tom

“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
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#20
I'm very near to you...so my experience may relate.

I prefer gas or propane heat when possible.

I installed a 105K BTU furnace in my shop in September 2014. It is fueled with propane. My shop is 1100 sq ft with 12 foot ceilings (13,200 cu ft). I installed R19 in the walls and R30 in the ceiling. The shop has two 16 foot wide overhead doors; both are steel, insulated and 8 1/2 feet tall. The doors have normal garage-style weather stripping.

When not in use, I kept the heat at 45 degrees. But there were stretches of a week or more where I set the heat at 60 or 65 degrees continually, usually because I was in the finishing phase or wanted the work pieces to be warmer.

My propane use for the season was less than 300 gallons.

The furnace has a dedicated 20 amp 120V circuit. 20 amp because that's what I decided to run for the 120V circuits all over the shop. It was about $1200 installed, including the plumbing for the gas and a thermostat.

I was always going to heat this space with propane; natural gas is not available and I didn't want to run more electrical capacity to the shop building.

I never thought OPPD electrical bills were high when I lived in Nebraska, but I really have no idea what a similar amount of heating capacity would cost in terms of energy use.

There are calculators that will help you size the heating unit, and you can figure out what their energy usage is from the spec sheet of the particular unit you are looking at. This is the one I used:

BTU Calculator

Good luck
Ray
(formerly "WxMan")
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#21
I think if you are able to get a true energy comparison, you're likely to find gas cheaper in the long run---it just depends on how long it will take to pay for the new gas line, heater and venting---to be amortized against the savings you'll have.

If you have natural gas in your house already----it wouldn't be that expensive to run a line----propane isn't as cheap as natural gas---and it tends to produce more water vapor.

Finally----assuming your walls are insulated----don't forget about your roll-up garage doors. Before I got a double wall insulated garbage door---all the wall insulation in the world didn't keep the cold out, with a leaky garage door.
Dave
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#22
Vented Gas or elect, neither changes the humidity in a space. They only supply a temperature rise, so matter what minute amount of moisture is in the gas makes no difference.

If you use liquid or nat gas, I would install a vented and sealed burner furnace so you have no open flames. This is most important in a garage and much more safe. It most likely will be code anyway.
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#23
Furnaces do change the humidity, but only because they take combustion air from the room and pull in very dry outside air. Not a huge difference, but I thought y might not know this living in tx.

It's a big problem here, we get cracked hands and faces from the dry air.
Mike

Non impediti ratione cogitationis
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#24
Estrogen Hostage said:


Furnaces do change the humidity, but only because they take combustion air from the room and pull in very dry outside air. Not a huge difference, but I thought y might not know this living in tx.

It's a big problem here, we get cracked hands and faces from the dry air.




Furnaces do not take air from the interior of the structure unless it is improperly installed. There is a duct to the outside in the furnace room/closet for combustion air so that air comes directly from outside and into the furnace.
Without it you are wasting lots of energy and increasing the risk of other issues like Co coming in the house if say the bathroom vent fans are runing.
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#25
Estrogen Hostage said:


Furnaces do change the humidity, but only because they take combustion air from the room and pull in very dry outside air. Not a huge difference, but I thought y might not know this living in tx.

It's a big problem here, we get cracked hands and faces from the dry air.






You cannot use combustion air from the living space in a home.
There are certain conditions to do so (Cubit ft per BTU's), and no modern home meets those conditions.

If you notice the vent pipe from any furnace, you'll notice a lot of vapor coming from it. That vapor is from the combustion air and very little from the fuel. That vapor does not enter the house. If it is, there is a serious and deadly problem.

Cold air holds less moisture. Warmed air can hold more moisture. Warming cool air causes a drying effect. The now warmed air that cools at a window for example will condense the moisture and cause sweating.
*A rough explanation.
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#26
daddo said:



If you notice the vent pipe from any furnace, you'll notice a lot of vapor coming from it. That vapor is from the combustion air and very little from the fuel.




Not quite sure what you mean by that, but the vapor is from the fuel to a large degree. When you burn a hydrocarbon, you get water. That's the vapor you see. Now the oxygen which makes up that water does come from the air, so it kinda comes from both the air and the fuel.
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#27
I have had Modine heaters run off an extra zone in the furnace. They were run off water whether from oil and later gas.
When in Massachusetts I had a two car garage (Colonial attached) with no heat. The walls and ceiling were insulated well. The windows were double pane. The temperature seldom went below freezing. The doors quality and were 2 inch insulated.
I question whether you need that large a heater. When you buy one the size can be determined from some calculation and from the heater supplier experience.
Paul from the beautiful mid-coast of Maine (USA)
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Garage heater gas or electric?


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