Electric garage heater

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Calculate the actual heat loss. Do NOT size a heater (or air conditioner) based on the square footage of floor space.

Insulate first. Stone wool with a radiant barrier is an awesome combination. After insulating, the heater might not be necessary; there might be enough Earth heat coming up through the floor.

This page is from ASHRAE 1993. The winter data's probably still reliable. The summer data, of course, has been rendered obsolete by global warming/global climate change.

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NTesla76 said:
It's an existing attached garage. Already insulated. If I had it my way, it would have been insulated differently, like you mentioned.
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With insulation, more is (usually) better. Can you add 1 or 2" foam panels all over? How 'bout the doors-- they're usually heat leaks.
Usually an infrared heater is most economical-- heat objects, not the air.
 
I agree with @drcampbell you want to calculate the actual heat loss.

How big is the garage? How many windows? How well are the walls insulated? Is the door insulated? How well does the garage door draft seal?

There are a number of online heat load calculators, but its been about a decade since I've had to do heat loss calcs.

Also, you need to define your heating goals: how much time do you intend to spend in the garage? Do you just want a cheap heater for now and then, or do you want to regularly heat the space? Would radiant heating (to make people feel more comfortable) or space heating make more sense for your intended use? Is your goal to heat the space to a human comfortable level on the coldest days, or just keep it above freezing for storage purposes?

-Jon
 
winnie said:
I agree with @drcampbell you want to calculate the actual heat loss.

How big is the garage? How many windows? How well are the walls insulated? Is the door insulated? How well does the garage door draft seal?

There are a number of online heat load calculators, but its been about a decade since I've had to do heat loss calcs.

Also, you need to define your heating goals: how much time do you intend to spend in the garage? Do you just want a cheap heater for now and then, or do you want to regularly heat the space? Would radiant heating (to make people feel more comfortable) or space heating make more sense for your intended use? Is your goal to heat the space to a human comfortable level on the coldest days, or just keep it above freezing for storage purposes?

-Jon
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It has 9' ceilings, 2 overhead insulated garage doors, 1 insulated exterior door and 1 double hung window. I'm not looking to keep it warm constantly, I just want to get it heated occasionally when I tinker around in the garage in the winter. I hate being cold.
 
NTesla76 said:
It has 9' ceilings, 2 overhead insulated garage doors, 1 insulated exterior door and 1 double hung window. I'm not looking to keep it warm constantly, I just want to get it heated occasionally when I tinker around in the garage in the winter. I hate being cold.
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I used a propane patio heater until I got the electric connected. IDR what the min setting is on the ceiling mount remote controlled one is, but that is generally where I set the temp. It takes too long to heat up a garage when its below freezing for several days in a row and 45-50 degree is comfortable enough to piddle around in.
 
If you just want occasional heat, then all of the comments about heat load calcs (including my own) go out the door.

First of all you don't need to optimize the system to be cheap to run, so you can simply go with an oversized electric. Why? Because you are trading higher running costs for lower initial costs and lower initial thinking costs.

Second because you don't need to worry about your worst case 'design day'. Maybe on your 99% coldest day the garage is too cold for tinkering. So you don't tinker on that day.

I'd go with one of the 4800W units that others have reported work well for them, and if you need get a second one.

If you want to spend a bit more, go with one of the fancy electric radiant heat units. They are nice for providing quick comfort without having to heat the entire space.

-Jon
 
winnie said:
First of all you don't need to optimize the system to be cheap to run, so you can simply go with an oversized electric. Why? Because you are trading higher running costs for lower initial costs and lower initial thinking costs.
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Oversizing also allows you warm it up faster if you decide to tinker at the last minute.

Another consideration might be that if your tinkering involves things like painting or staining things, you may not want forced air anything because it tends to stir up dust that will end up embedded in the finish.
 
letgomywago said:
What's the garage height. If tall go radiant unless you have a large fan.
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winnie said:
If you just want occasional heat, then all of the comments about heat load calcs (including my own) go out the door.
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Hear here.
Especially with electric resistance heat, which doesn't become less efficient when it's oversized. (although it may become uncomfortable)

winnie said:
... lower initial thinking costs. ...
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Please tell me you didn't really just say that? It's a residential heat-loss calculation, not the Navier–Stokes equations.
 
winnie said:
I agree with @drcampbell you want to calculate the actual heat loss.

How big is the garage? How many windows? How well are the walls insulated? Is the door insulated? How well does the garage door draft seal?
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(How well) is the ceiling/attic space insulated? The ceiling is by far the largest surface where heat loss can occur.
 
ggunn said:
... The ceiling is by far the largest surface where heat loss can occur.
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All generalizations are false.
Including this one.

Consider a 20x20x8-foot attached garage:
400 ft2 of ceiling area
480 ft2 of exterior wall area
160 ft2 of interior wall area

Gross area isn't necessarily directly proportional to heat loss, (or gain) as the individual components are likely to be built and insulated differently.

Your results will vary, but it's a simple matter to list all the components on a spreadsheet, with their actual dimensions and a good estimate of their individual heat-transfer characteristics.
 
drcampbell said:
All generalizations are false.
Including this one.

Consider a 20x20x8-foot attached garage:
400 ft2 of ceiling area
480 ft2 of exterior wall area
160 ft2 of interior wall area

Gross area isn't necessarily directly proportional to heat loss, (or gain) as the individual components are likely to be built and insulated differently.

Your results will vary, but it's a simple matter to list all the components on a spreadsheet, with their actual dimensions and a good estimate of their individual heat-transfer characteristics.
Click to expand...
I was considering each wall as a separate surface, so no, it wasn't. For my attached garage, each of the four walls is different.
 
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