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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