David,
I'm comfortable in working temps around the upper 40s to upper 50s so
anywhere in that range would be workable. I'm not trying to totally
heat the building. I just want something to make it comfortable and
take the chill off while I'm working on something.
Using a few portable heaters this coming winter will give me an idea
as to how warm I really would like it and whether spot type heating is
sufficient. If not then I'm going to have to come up with a better
solution.
The roof is actually better than the walls. It has the R4 insulation
that laid over the rafters then on top of that there are 2x4s placed
90 degrees to the rafters and on top of that is the roof decking and
shingles. So there is an air gap between the roof decking and the
insulation. It seems to block the effects of the summer sunshine
pretty well.
Brad
On Wed, Jun 9, 2010 at 11:11 AM, David Scheidt <dmscheidt@gmail.com> wrote:
> On Wed, Jun 9, 2010 at 9:07 AM, Brad Kahler <brad.kahler@141.com> wrote:
>> Yeah I know its summer but for me it s time to start thinking about
>> how to heat the new shop.
>>
>> Background info: 40' x 50' with 12' metal side walls and metal roof,
>> R4 insulation, clear span and an 18' peak inside with concrete floor.
>> Also there are 3 turbine vents on the roof for ventilation that could
>> be closed off during the winter if need be.
>
> First step in any heating system design is to figure out what the heat loss
is.
> without that, you're going to buy too much or too little heat. Either
> is expensive.
> A big part of that is climate, which you haven't told us. Another is
> what temperature you're going to keep it at. (45 or 50 isn't awful to
> work in, will keep things from freezing, and when you're going to be
> out there for a while, you can turn the heat up.) That's because heat
> loss goes up as the difference between inside and outside temperatures
> go up.
>
> There's software that does this; any competent HVAC system contractor
> will have something. (it's 2010; not having the software means he's
> stuck in 1970, and probably hasn't changed what he does since. Sadly,
> there are many HVAC contractors who are total morons about how to size
> a system.) It also makes it easy to see what changing the building
> does to the calculations (adding insulation, improving windows and
> doors, etc). R4 is about an inch of fiberglass; you may not be able
> to improve the walls, but I bet you can the roof.
>
> Once you know how many BTUs you need, you can think about the ways to
> get them.
> It's worth paying someone to do the numbers. (At a rough guess, a
> building like that, aorund here (N. Indiana), would require something
> in the range of 30 btu/square foot.
> You're at 2000 sq ft, so something on the order of 60K btu. You many
> need more or less, depending on a lot of things. 60K BTU/hr is about
> 18 kW, that'll require 100 amp service, just for the heat. ) Buying
> too much heat is expensive upfront, and it'll cost more to run, and
> not last as long. Buying too little means you get cold.
>
> (As an aside, I used to work in a shop with overhead radiant heat. It
> would have been hard to have designed a worse heating system for the
> shop. it was bigger than yours, and had a much higher ceiling, but
> all clear span. It was kept about 60 or so. You'd open an over head
> door, and all the heated air would be lost. Then you'd drive a cold
> (and probably snow covered.) car into the bay, and put it on the
> hoist. The heat would come on and heat things up. Except it was
> aimed at the car, and not the person working on it. So you'd be under
> the car, which sucked all the heat out of the place, and about the
> time it got not awful, you'd fixed it, and it was time for the next
> one. Maybe not a problem in a home shop, but something to think about
> with radiant heat.)
>
>>
>
>
>
> --
> David Scheidt
> dmscheidt@gmail.com
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