My recommendations would be-

a) Three words- GFI

b) A thermal switch mounted to the cabinet that will kill power if the
temp gets too high. You may also want to consider lining the case
with insulation to keep it's outside temperature resonable.


9.6 kw is around 32K BTU, I'm not a heating engineer but I don't think
that's going to do a whole lot of rapid heating. If your garage isn't
well insulated you may find your heater is going to be running
continuously for not much effect. I've got a 125K forced hot air oil
furnace in our 20x30 (uninsulated/drafty) shop & it takes about an
hour to get the place & everything in it from freezing into the low
60s. That's with a duct sytem to get heat spread around evenly.


Have fun,

Howard.

http://users.eastlink.ca/~howarde/



On Fri, 30 Dec 2005 16:52:43 GMT, Ignoramus24987
wrote:

I have a approximately 20x20 ft attached garage. Sometimes I want to
make it warm quickly. Often I am there for relatively short periods of
time (because I am constantly interrupted).

I bought a 9.6 kW, 240V duct heater on ebay. It has a 24V control and
various overheat protections.

My plan is to enclose it into a welded frame and sheet metal (found a
few nice sheets in a hospital dumpster), add a fan to it and a 24V
control system using a thermostat. I also have a grill type thing that
I can use to protect the coils from little curious fingers and
flammables.

My idea is to make something relatively compact (say 2x2x1.5 ft), that
I would set on the floor, turn on and get the garage warm in a few
minutes rather than wait for a long time. I would save some
electricity by only heating the garage when I need it, rather than
warming it up "just in case".

What I am looking for is some feedback on safety and such.

i

Ignoramus24987 wrote:


That's one word
But pronounced as 3


My garage is attached to the house. It is not drafty.
But not airtight either
I am not a
heating eingineer either. To me, 9.6 kW is an incredible amount of
heat.

My shop has 108 kg of air.

But how much moisture


Its heat capacity is about 1,175 j/kg/degree C.

To warm 108 kg of air by 20 degrees C (about 45F), would take

1175*108*20=2538000 joules.

Since a 9.6 kW heater produces 9,600 joules per second, the time to
raise temperature of air by 20 degrees would be

2538000/9600 = 264 seconds, or about 4 minutes.

This calculation ignores the effect of cold walls and objects in the
garage that cool air, which would have a significant effect. Still, I
should expect this to work reasonably.

It also ignores the fact that you are having [even though not drafty]
several complete air changes per hour. Chances are that most of that
is outside air, not house air.
jk

In article ,
Ignoramus24987 wrote:

On Fri, 30 Dec 2005 19:58:34 GMT, Howard Eisenhauer
wrote:
My recommendations would be-

a) Three words- GFI

That's one word

But thanks.

b) A thermal switch mounted to the cabinet that will kill power if the
temp gets too high. You may also want to consider lining the case
with insulation to keep it's outside temperature resonable.

Great idea.


9.6 kw is around 32K BTU, I'm not a heating engineer but I don't think
that's going to do a whole lot of rapid heating. If your garage isn't
well insulated you may find your heater is going to be running
continuously for not much effect. I've got a 125K forced hot air oil
furnace in our 20x30 (uninsulated/drafty) shop & it takes about an
hour to get the place & everything in it from freezing into the low
60s. That's with a duct sytem to get heat spread around evenly.

My garage is attached to the house. It is not drafty. I am not a
heating eingineer either. To me, 9.6 kW is an incredible amount of
heat.

My shop has 108 kg of air.

Its heat capacity is about 1,175 j/kg/degree C.

To warm 108 kg of air by 20 degrees C (about 45F), would take

1175*108*20=2538000 joules.

Since a 9.6 kW heater produces 9,600 joules per second, the time to
raise temperature of air by 20 degrees would be

2538000/9600 = 264 seconds, or about 4 minutes.

This calculation ignores the effect of cold walls and objects in the
garage that cool air, which would have a significant effect. Still, I
should expect this to work reasonably.

Umm. The air in the room is only a heat transfer fluid. You are
heating the floor, walls, ceiling, and of course the iron toys. (Plus
any air leaks from the outside.) These will weigh orders of magnitude
more than the enclosed air.

The specific heat of materials other than water is about the same as for
dry air, in terms of weight. So, add it all up.

Joe Gwinn

Howard Eisenhauer wrote:
9.6 kw is around 32K BTU, I'm not a heating engineer but I don't think
that's going to do a whole lot of rapid heating. If your garage isn't
well insulated you may find your heater is going to be running
continuously for not much effect. I've got a 125K forced hot air oil
furnace in our 20x30 (uninsulated/drafty) shop & it takes about an
hour to get the place & everything in it from freezing into the low
60s. That's with a duct sytem to get heat spread around evenly.

Last night I was working in our shed. It is an uninsulated brick
building maybe 10' x 18'. It was below freezing outside so I took a 2 kW
electric fire with me. It didn't heat the place fast, but after 1/2 hour
it was quite bearable. Howard is probably right when he says you
shouldn't expect instant heat, but I think it'll be a significant
improvement on no heat.

An interesting aside is that a human being on average radiates 84 W of
heat. That would be like having over 100 people in your garage. Given a
little time to warm up, I think it'll make the place comfortable :-).

Chris