Estimates on BTU required

[biggziff]

I'm wondering if anyone here can give me an idea of how many heat BTU I'll need for my new shop? 27 X 36 X 12.5 ceilings, 2X6 walls and 2X8 ceiling bottom chords, 14X10 and 10X10 R20 overhead doors. By mid-spring I'll have it insulated with dense pack cellulose and the walls covered and a ceiling installed. I'll mainly be spot heating when I'm out there, but may want to keep it just above freezing for the winter (at least until I see the gas bill) LP gas.

Thanks

 

[Andy8430]

Sounds like you’ll be well insulated. I’d guess about 75,000 btu.
That’s what I have in my 1600 sq ft garage with 9’ ceilings (R38 in ceiling, spray foam in walls).

I’d suggest having a heating company quote it. Then you can see if it’s worth your time and they’ll size it for you as well.


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[biggziff]

Sounds like you’ll be well insulated. I’d guess about 75,000 btu.
That’s what I have in my 1600 sq ft garage with 9’ ceilings (R38 in ceiling, spray foam in walls).

I’d suggest having a heating company quote it. Then you can see if it’s worth your time and they’ll size it for you as well.


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I'd only be heating to 50-60 when I work in there. Does your 75K short cycle in that space? What temps do you heat to?

 

[biggziff]

Also, my dad just suggested when he bought his heater someone told him he'd have to consider how high the unit would be mounted as they're only rated to push heat/air down so far based on BTU (and I assume fan size/speed)? Does that make sense?

 

[zmotorsports]

Your shop is just barely smaller than my last shop and I had a 75k btu Modine Hot Dawg in my last shop. Worked great, got up to temperature in an acceptable amount of time and didn't short cycle. Usually kept it around 50 when I closed up for the night and would bump it to 62~ish degrees when I arrived home from work and was going to go out and work in the shop. By the time I would go in the house, change and grab a drink and walk back out to the shop the T-stat was either satisfied or very close to it.

 

[Andy8430]

I keep my garage around 55 degrees and bump it up when I’m working out there.
On a cold winter day (0 degrees outside), I’d estimate it’ll run 10 minutes once an hour. I’m sure a smaller heater would work as well, but chose this unit as the cost increase was minimal and physical dimensions were the same.
FWIW: it’s a Modine Hot Dawg HD75AS0111 running on natural gas.


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[biggziff]

Just got confirmation from Mister Heater that max height for the 50K is 10' (floor to bottom of unit) and 12' for the 80K and 125K units. I guess that makes my decision for me. 80K for me.

 

[Andy8430]

I think you’ll be happy with the 80k unit. Good catch on the ceiling height affecting the choice.


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[biggziff]

I think you’ll be happy with the 80k unit. Good catch on the ceiling height affecting the choice.


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Thanks for the reply. At $319 shipped, it's pretty hard to ignore these 80K Mister Heater units. I'm guessing they're all made by the same company somewhere in Asia.

 

[finn]

80k is way oversized for that small of a building if it is well insulated, and you are planning on continuously heating the space rather than bringing the temp up from dead cold on a regular basis.

Heat is most comfortable if the unit runs longer, rather than short cycling in cold weather.

I have 75k units in two different buildings, a 32x54 with 10&12’ ceilings and a 32x75 with 16’ ceilings. I could probably make a smaller unit work in the smaller building, but I don’t heat it continuously.

I’m not sure what the issue is with your ceiling height. I mounted the unit with the 16’ ceilings off the wall at about 10’ with a hanger I built from unistrut.

 

[biggziff]

80k is way oversized for that small of a building if it is well insulated, and you are planning on continuously heating the space rather than bringing the temp up from dead cold on a regular basis.

Heat is most comfortable if the unit runs longer, rather than short cycling in cold weather.

I have 75k units in two different buildings, a 32x54 with 10&12’ ceilings and a 32x75 with 16’ ceilings. I could probably make a smaller unit work in the smaller building, but I don’t heat it continuously.

I’m not sure what the issue is with your ceiling height. I mounted the unit with the 16’ ceilings off the wall at about 10’ with a hanger I built from unistrut.

I do not plan to heat it continually. There may be times when I do, but it will likely be for a project that may take days to complete at most. For $60 more I bought the larger unit. I can easily de-rate it with smaller orifices or cap one of the burners. I've done this on other furnaces and it works well. I'd rather have too much than too little.

The air handling capacity is higher with the larger units (750 CFM for 50K and 950 CFM for 80K) so the larger fan can move more air and at a higher velocity which should allow it to push more air further towards the floor. Makes sense to me and it was how Mister Heater explained it.

 

[Andy8430]

Thanks for the reply. At $319 shipped, it's pretty hard to ignore these 80K Mister Heater units. I'm guessing they're all made by the same company somewhere in Asia.

That is a great price. Less than half the cost of the Modine I installed last year.


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