Calculating heat requirements

[Moses Yoder]

It really burns me to spend money for heat. It is basically taking a dollar and lighting it on fire. Thus I don't heat my shop in the winter. I spend most of the winter indoors reading in my spare time, stirring the pot on the web, etc. In another facet of my life, I am phasing my shop down to use only one side of a 2 car garage, so my wife can put her car in the garage. I will use mostly hand tools but roll my table saw into the car bay to use. I will also have a band saw and lathe. In the winter I am thinking of hanging a heavy curtain to divide my half of the shop into a half, or one quarter of a 24 x 28 shop. I have a vintage Coleman gas plant, the 460G, that works fine and puts out 55,000 BTU. Would it be reasonable to expect this heater to heat my quarter shop? I can buy white gas for it at $5 per gallon since I live in Amish country. With this small heated area I could do carving or make planes, etc. We live in a small house with no basement, so those are not options.

[Jim Andrew]

I don't know if your garage is insulated, but if it is reasonably insulated a 55,000 btu heater should heat the entire garage.

[Moses Yoder]

I don't know if your garage is insulated, but if it is reasonably insulated a 55,000 btu heater should heat the entire garage.

What formulas did you use to figure this out? How long would it take to heat up to 60° from 10°? How much fuel would it use?

[John Stankus]

What you are looking for is a "Manual J" calculation. There are a few free Manual J calculators on the web for simple buildings, they get more complicated for whole houses. I used one of the calculators when sizing my minisplit in my garage (unfortunately don't remember which one). What the calculator will do is have you model the size and construction of the walls floor and ceiling. Coupled with the temperature difference you want to maintain it will indicate how big of a heater you need. And as always more insulation is better. The less insulation the more of your heat escapes, and is not available to keep you toasty. One thing you may want to be careful of with a gas heater is maintaining proper ventilation and make-up air. Carbon monoxide poisoning can easily happen.

John

[Tom Stenzel]

Hi Moses,

Just as a data point.

I have an old Perfection 300 kerosene stove, and a not quite as old Kerosun stove. I'm guessing that together they put about 20,000 BTU. In my uninsulated 2 1/2 car garage with crooked concrete creating gaps under the garage door (as in snow blowing in), with both heaters running the temp would go up about 25 degrees over ambient. For my use that was enough. Normally I was out there to repair a car so I only heated the garage a few times each winter. Hanging a rack over one heater to warm the tools helped.

-Tom

[Jack Jackson]

For the life of me I can't remember where I read this but I saw a somewhat simple calculation at some point that I remember... sqft that needs to be heated X 60 (for cold climate, or in your case since it's a garage with only 3 solid walls) and then divide that by the efficiency of the heater
So you have 1/4 of a 24 x 28 = 168 sq ft
168 sqft X 60 = ~10,000
A complete guess on the efficiency is about 40-50% (since a central heat system is usually 80%ish... guesstimate) - 10,000 / 0.4 or 0.5 = 20,000 - 25,000 BTU

Even if that formula or calculation is off by 50% or more then you should be more than ok with a 55k BTU heater.... maybe that helps. Probably also depends on how well the blanket wall acts as a partition... As for how long and how much fuel? That's out of my league.. the fuel part is probably a pretty specific attribute of your particular heater. But assuming you could heat that space with half that amount of heat output then I wouldn't think it would take long to get it heated up to manageable....

Good luck

[Perry Holbrook]

Looks like 1 gallon of gasoline is 124000 BTU. At 80% efficiency, that's roughly 100000 BTU per gallon. So if your unit really is 55000BTU output, that about 1/2 gallon per hour.

Just my opinion here but I would be very un-easy using gasoline as a heating fuel in a wood shop (or anywhere) so many ways for things to go boom.

Perry

Perry

[Lee Schierer]

I don't know if your garage is insulated, but if it is reasonably insulated a 55,000 btu heater should heat the entire garage.

I heat my entire house in NW PA with that size heat output......1400+ square feet.

[Jason Roehl]

If you have a white gas burner going at 50% efficiency, you're going to have a whole bunch of noxious fumes in the area.

Furnaces are 80-95% efficienct because they vent the exhaust gases and have to maintain a stack effect in the lower end of that range. A heater that burns with a completely blue flame with no venting will be near 100% efficient.