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Old 10-18-2008, 10:28 AM   #1
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Metal Building Heat


I have a 40ft. X 30ft. 15ft. eve insulated metal building,with 2 roll up doors.I live in central NC.I am wanting to put in a hanging heat system (gas or elec.).My question is what kind of btu heat will I need and which is most efficient gas or elec.?
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Old 10-18-2008, 11:38 AM   #2
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I have a 40ft. X 30ft. 15ft. eve insulated metal building,with 2 roll up doors.I live in central NC.I am wanting to put in a hanging heat system (gas or elec.).My question is what kind of btu heat will I need and which is most efficient gas or elec.?
Thanks
I use the rough calculations of cu ft of the area to be heated times 5 btu's per cu ft. Yours would end up at 22,500 btu's.

This is just a rough calculation. If you live in a moderate climate where it doesn't get below freezing then a smaller unit might do. If you live in a very cold area then a slightly bigger unit might be required.

I have no idea what the weather is like in central NC so I can't say what you need. But my guess is that in the neighborhood of 20,000 btu's is a good place to start.

I like gas. It just seems warmer.

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Last edited by Marvin Gardens; 10-18-2008 at 11:49 AM.
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Old 10-18-2008, 12:21 PM   #3
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Metal Building Heat


My 0.02 cents Go with a gas fired tube heater. Thats the way to go!
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Old 10-18-2008, 01:34 PM   #4
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Quote:
with 2 roll up doors
If the roll up doors aren't well insulated or sealed, you'd need to upsize the unit to take that into account vs. just going by cu. ft. Sorry, kind of a vague statement, but w/o testing the heat loss it would be hard to say how much you'd have to upsize..
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Old 10-18-2008, 02:05 PM   #5
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The doors are not insulated and definately not sealed.So maybe double the btu's?
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Old 10-18-2008, 03:45 PM   #6
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The doors are not insulated and definately not sealed.So maybe double the btu's?
No need to double the btu's.

A heater is just to heat the air. It needs to find a nice balance of heating it in reasonable time.

If it heats it too fast then it is on a short time and cycling on and off a lot is not good. Equipment is measured in cycles for it's life.

If it is too small it will stay on for a long time and won't really get the place warm. This means that it is inefficient.

For your place 22,500 will get the place warm in reasonable time. It will just have to come on sooner to replace the heat loss through the doors.

A larger furnace will heat it quicker (and cycle more often) but will do nothing for the heat loss through the doors.
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Old 10-18-2008, 04:09 PM   #7
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We got a recovery time problem with the doors. Everytime they open he is going to lose all the heat that is in the struture.

Gotta figure 40% more for that.

Gas radiant heat is more suited to to structure you have and will not have to be sized larger to compensate for loss recovery.
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Old 10-18-2008, 04:39 PM   #8
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Gas radiant heat is more suited to to structure you have and will not have to be sized larger to compensate for loss recovery.
That's a good idea. Little more expensive up front but much better in the long run.
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Old 10-18-2008, 06:07 PM   #9
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Thank You all for the replies.I just found this place today and joined and am more then impressed.
Thanks Again
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Old 10-18-2008, 06:10 PM   #10
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So,are you saying to figure 40% more to the 22,500 to compensate for the heat loss?My calculations are 31,500btu's
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Old 10-18-2008, 06:37 PM   #11
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1200 sq ft with a 15 ft ceiling?

48000 minimum. Screw that 5 btu per cubic foot. Might be good for a super insulated residence but not a commercial bldg.

If you use hanging unit heaters you are going to have more heat at ceiling level than at the floor. Gonna be on helluva gas pig. Your bill is gonna be through the roof.

Better to use a ducted system bringing the branches to floor level.

Or use a down-flow furnace furnace and run duct along the walls at floor level.

It's either that or radiant heat as your best bet.
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Last edited by hvaclover; 10-18-2008 at 06:52 PM.
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Old 10-18-2008, 11:20 PM   #12
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How insulated is the building. Whats the R value. Is it fiberglass, or foam.
Any windows in it. If so, what kind, what size.

Are you going ot work on motors/engines that you will run in the building, meaning you will have mechanical exhaust may be.

How warm do you want to keep this building.

Are you going to turn the heat down at night , and then want quick recovery in the morning.

Is the slab insulated.

I'm tired, or I'd ask more questions.
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Old 10-18-2008, 11:56 PM   #13
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it's gonna be radiant Been just kiddin.
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Old 10-19-2008, 07:45 AM   #14
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Yes...15 foot ceiling at the peak.It is fiberglass insulation wrapped in plastic.Not sure of the R value, probably not that high.No windows.No exhaust system.I'm not out there but a few hours during the week but pretty much all day on weekends.I would like to keep the building around 50 degrees at all times to keep things from sweating.The slab is not insulated.
Now for my stupid question as I'm not that familiar with hvac.
What is radiant heat?
Thanks again,
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Old 10-19-2008, 10:37 AM   #15
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Gas radiant heat throws heat like an electric heater but burns gas instead.
They are smal units that would heat the slab as if the sun were beating on it.

Do a Google search. The place I bought stuff from is Detroit Radiant in MI.

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