Heating Requirement Calculation

[foglght]

I've been to probably 100 websites and contacted a few installers about what type and size heater I need. Nobody can seem to agree on what the best option is. The cost to run a natural gas line out to my barn is prohibitively expensive, so I am considering a heat pump.

Garage size is: 30x40x14. It isn't insulated right now, but it will be. There are two doors (9x9 and 13x12). 6 windows (regular dual pane).

When I use some of the calculators it tells me I need a 120,000BTU heater. Some calculators say I need a 28k BTU heater. That is a massive difference.

The reasonable calculations I have done seem to say I need about a 60k BTU heater for about a 35 degree rise.

One installer says I need a full 100k BTU NG ceiling mount, while another guy says that is WAY overkill and I need a 36k at most.

I don't want to do this more than once. I figured people have done enough garage projects here to know....I'm in Michigan. Was hoping to be able to keep the garage just above freezing for a lot of the car care products that I don't want to lug in and out of the house. Not sure I would do that, but don't want to have to wait 6 hours for it to heat up if I need to do work on the RV or other cars.

 

[Showkey]

1200 sqft with insulation in cold climate using any ball park calculation gets your 60-80k NG or propane heater.

Many of us are not going to buy into heat pumps in true cold climates. Heat pump will take for ever to warm the garage from storage temp to working temp.

Nothing is cheaper in the long run than lots of insulation and NG.
I have a 1000 sqft cold climate 45k NG ceiling mount with very good insulation works well at a very low cost. Replaced a 60k unit ( failed) that recovered faster.

 

[earlybirds]

Showkey is right. Insulation and NG is best in the long run.
I also have a 30x40 shop that I heat only when I'm using it. I use a 100,000 BTU input(83,000 output) Modine hanging unit heater. Living in Iowa, we also have COLD winters like you. This heater brings the temp. up from 20 degrees to 60 degrees in about 15 minutes. Love it! I have only average insulation in my shop. R15 walls & roof.

I have read numerous posts online about guys that have regretted installing a too small heater. I guess it depends on your shop heating schedule.

BTW, I ran a 150' NG line to my shop for about $900. Not that bad.

 

[yeldogt]

HP like AC needs to be sized for maintained temp -- what you are trying to do is like showing up at a beach house when it's 100 outside and 85 inside and expecting the AC to bring the inside temp down to 70 in an hour ..... not going to happen.

I heat my well insulated 1700sf studio with an 80% 40K BTU Propane unit. It's a Empire DV40E floor mounted sealed combustion cabinet heater. When using the space often I keep it around 68 .. if away a week or two I drop down to 60. 40k BTU at 80% is only 32K BTU's... my heater does not need to run all the time even when it 5 degrees outside. But, everything in my studio is at a constant temp. I also can't work all bundled up w/ gloves on.

A full garage will take longer to heat vs one that's empty -- everything in the space needs to be heated. Starting temp/ average outside temp/ insulation/ weather tightness all factor into the size needed.

Many people have older spaces w/ little insulation -- non insulated garage doors ... that type of space is going to need a big heater as much of the heat is going outside. Some people work in heavy clothes ... also, a big heater overheats the air and cycles often.

The best advise I can give is spend the money on great insulation good doors -- the payback is forever in energy and comfort. I would get a few quotes on what the NG line will really cost. I don't have NG .. so it's only propane. Actually will be adding a HP to my space .. I want to fully AC my studio and the HP will protect me from propane spikes.

The only way the HP is going to work is if you insulate well and maintain the temp.

 

[foglght]

Showkey is right. Insulation and NG is best in the long run.
I also have a 30x40 shop that I heat only when I'm using it. I use a 100,000 BTU input(83,000 output) Modine hanging unit heater. Living in Iowa, we also have COLD winters like you. This heater brings the temp. up from 20 degrees to 60 degrees in about 15 minutes. Love it! I have only average insulation in my shop. R15 walls & roof.

I have read numerous posts online about guys that have regretted installing a too small heater. I guess it depends on your shop heating schedule.

BTW, I ran a 150' NG line to my shop for about $900. Not that bad.

If the quote to run a gas line was 900 i would have done it already. Best quote so far was 2,800 and I dig the 24 inch trench. All said and done I'm talking about 5k.

Was considering hiding a propane tank in my shed just behind the barn and running a short line into the garage. Need to do some calculations to see how long a 100lb tank would last only heating when necessary.

I do have good commercial 2 inch thick garage do0rs. Haven't figured out what I'm going to do for insulation and walls. If I have to spend 5k on a ng setup I may not be able to do it this year.

 

[mrpizza]

Even insulation alone will help keep your space more comfortable. I sprayed 2" closed cell foam to all walls and ceiling in my garage. When it was 10 degrees outside, it would maintain 40 in the garage. Until I opened one of the big doors and let all the heat out lol

 

[matt_i]

Heat pump is a no-go in Michigan imo.

Propane or NG.

I have a 100k furnace in my shop (25x40), its plenty of heat and so the temp rises quickly when I spool up the jets so to speak. I usually hold it at 35F and then ramp it up to 50-60F for work sessions.

I believe even a 36k BTU would keep your space above freezing, but might take a long while to get it up to full temp. I would try in the 60-80k BTU range if you can.

As the others have said, air sealing and insulation are key.

 

[earlybirds]

If you dig the 24"deep trench, you have 90% of the work already done. Running the gas line is super simple using polyethylene gas line. Many contributors to this forum have done the work themselves.

 

[yeldogt]

I'm doing a buried 1k at the property now -- I previously used two 100gallon (not LB) for the heater supply.

With propane you need big enough tanks to supply the pressure and open area for the liquid to turn to gas -- you can't just attach any tank and expect it to work.

5k buys a fair amount of insulation. Spend the money on spray foam -- you will need a much smaller heater (less cost) and be able to keep the space at a higher temp w/o extra cost in fuel. Spray foam is not just a little bit better -- it makes for a different building. Look into getting a flash and batt setup ... layer of foam to seal up the building and eliminate condensation -- add batt for extra R value.

 

[foglght]

Well, many contractors later and a whole lot of headache; I managed to get heat in the garage. I found a guy who would sleeve a pipe under the driveway. I just finished having the drywall mudded and taped, so he installed the heater. Works great!

Finally its coming together. Ceiling insulation going in on Monday and then paint.

Total cost for the gas line and the heater was $4,200.

 

[shaggyant]

And how many BTU heater did you end up with?

 

[foglght]

Waffled a bit on that but ended up with a 75k unit

 

[shaggyant]

Let us know how it works when winter hits.

I’ve got a 36x48x14 shop I’m looking to put a gas unit heater in and I’m debating on going with the 80k I already have or buying a 100k for a faster recovery.