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Old 11-07-2012, 10:26 AM
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Separated combustion shop heater

I'm pricing a heater for my new shop, looking at the hanging style propane heaters. Since I plan to use solvents and paint when the heat is on, I'm looking at separated combustion heaters where the combustion air is drawn from outside the building using a separate tube instead of from inside the building. Most vendors (Modine, etc) sell both conventional vent and separated combustion versions of their heaters, but the separated combustion versions carry a 60%-100% price premium. As an example, the one I'm considering is about $450 for conventional and $750 for separated.

I've downloaded the manuals for these units, and the only difference between the two is that where the conventional units simply have louvers in the sides where the heater draws combustion air in, on the separated units these louvers are blanked off and a 4" pipe connection is provided instead that is routed to outside the building. The only other thing is that the separated units have additional gasketing inside the case to ensure that no inlet air can be drawn from inside the building. Everything else in the unit - blower, burners, propane nozzles, etc, all have the same part numbers between the two units.

$300 extra to NOT punch louvers?! Seriously? Yeah, I suspect a large part of that price difference is for product liability insurance and lawyers, but you know what my next question will be. Why can't I seal up the inlet side of a conventional heater, blank the louvers, and add a pipe connection to outside? Assuming the airflow is the same (and the separated units all use standard 4" galvenized duct), the burner won't know the difference. This is even more attractive because used conventional vent heaters are readily available for even less money, but I have yet to find a used separated combustion unit.

Thoughts from HVAC guys?

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Old 11-07-2012, 01:52 PM
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I'm not an HVAC guy, but consider this - If the worst should happen and your shop catches fire, do you think the insurance company is going to pay off once they see you modified the heater? Is that, or the possibility that you overlooked something in your mods, worth $300?
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Old 11-07-2012, 02:08 PM
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Originally Posted by sedanbob View Post
I'm not an HVAC guy, but consider this - If the worst should happen and your shop catches fire, do you think the insurance company is going to pay off once they see you modified the heater? Is that, or the possibility that you overlooked something in your mods, worth $300?
Are you an automotive engineer? What will the insurance company (and lawyers) say when they find out that you used non-stock brakes on your street driven car and had an accident? Same logic applies yet that issue never comes up on this forum.

And yes, I did consider that and I'm quite confident in my ability to mitigate that risk.
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Old 11-07-2012, 04:33 PM
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As long as those brake parts meet or exceed the manufacturer's specifications, you are covered. Just like doing your own oil changes - as long as you use oil that meets/exceeds specs, they can't void your warranty. They used to, until they lost that fight in court.

I wasn't telling you what to do, only advising you of the potential consequences. I don't have a dog in this fight.
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Old 11-08-2012, 09:12 AM
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As long as those brake parts meet or exceed the manufacturer's specifications, you are covered.
I'm talking about installing a complete front clip on an older car, for example, or a rack and pinion conversion, NOT simply using aftermarket replacement parts.

Back to the original question, the change I'm talking about on the heater is equivalent to removing an open element air cleaner and installing a sealed air cleaner with ducts to scoops under the front bumper (and yes, I DO own a couple of Olds W-30s... ). This is why I'm not particularly worried about the risk.
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Old 11-08-2012, 12:05 PM
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Iwould want to take a look at the particular unit tha tyou propose to modify as the ones that use outside air have what we call a divorced heat exchanger so there is no possibility of exchage of interior and exterior air within the heating unit..What you wish to do sounds reasonable..

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Old 11-08-2012, 12:20 PM
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Quote:
Originally Posted by joe_padavano View Post
Are you an automotive engineer? What will the insurance company (and lawyers) say when they find out that you used non-stock brakes on your street driven car and had an accident? Same logic applies yet that issue never comes up on this forum.

And yes, I did consider that and I'm quite confident in my ability to mitigate that risk.
don't know what your laws are there..
but I can't run a propane heater like that if I have n.gas on site..
also having a torch set in the garage is a nono.. I have to store them in a shed away from the house and garage (garage is detached)
I'd look into it with your insurance before.. going any father.. as the post above shows you haven't even called them and asked..

good luck with whatever you choose..

remember the fire marshal will find the cause and you don't want to find out then that, something you did cause's your insurance to not cover any claim..
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Old 11-08-2012, 12:41 PM
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I am having a new 12,000 btu forced-air Heater installed in my Shop today-I had two Electoric ones installed about 2-3 Years ago, and they burned out quick and were so noisy I couldn't hear the Radio -

I thought about going back to the Electric ones (for Painting purposes), but, obviously, they are more expensive to run (and with the noise thing ), I decided to go forced air-part of the downside (for me) is that they have to core-drill my Shop (it is cement walled) for the exhaust-they are doing that now-

As for Painting, I decided that I would Heat the place up, shut off the Heater and run some small ones (Electric) to keep the Heat-not the best solution, but as I am just a hobby guy I'll live with it (you know the old saying, it's a tough job but someones got to do it...........)-

Good luck with whatever you choose to do, but I think I would talk to my Insurance Carrier to make certain they are ok with it-
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