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Used Gas Heater?


gloveguy's Avatar
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01-27-17, 02:50 PM   #1 (permalink)  
Used Gas Heater?

Hi there,

I've got a 40'x40' shop with 18' ceilings. The building is well insulated and I'm just in the process of, finally, sheeting the inside of the shop. Also, there are two variable-speed ceiling fans to move air around.

My question is has anyone had good experience in buying a used forced-air furnace? I've seen a few come-and-go on Craigslist over the past couple of years and it makes me think this could be an option.

In my area (Vancouver-area, BC, Canada) a hanging-style "Unit Heater" (Modine) goes for about $2600.00 CDN. The unit would only be used for about 4 months of the year, as I'd only need it on to top up my room temperatures for certain tasks like painting/finishing, etc.

I know the heat exchangers are the big ticket items for furnaces, and I've always been a bit skeptical as to why someone would sell a furnace in "good working condition."

I've got a friend who's a licensed gas fitter who can get me hooked-up and vented so I'm not concerned about the actual installation of the unit.

Here's a link of a current listing, in my area, as an example:
https://vancouver.craigslist.ca/van/hvo/5976545102.html

Any advice on this would be greatly appreciated.

Thanks for reading my thread!

 
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PJmax's Avatar
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01-27-17, 03:46 PM   #2 (permalink)  
That one you linked to is 125k btu. It may be a little large for your requirements.

When you buy used it's called...... "the luck of the draw".
Me buying something used is completely different then you buying something used.

I generally buy a lot of used equipment but I know how to fix it. If you aren't mechanically handy your used purchase could cost you money.


~ Pete ~

 
gloveguy's Avatar
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01-27-17, 05:54 PM   #3 (permalink)  
@PJmax... Thanks for the reply.

Yeah, I was wondering about the size, too.

I had a furnace guy out to my property as I was having an 80,000 BTU furnace serviced in a neighbouring rental space and, although he didn't do an assessment on the heating requirements of the shop, he thought the 80,000 BTU unit was a bit small for the shop.

Also, I wanted a hanging-style unit heater rather than a traditional up-flow house furnace.

In the past I've tried out a couple of online BTU calculators and one told me I needed 55,000 BTUs and the other said 75,000 BTUs. Then when the furnace tech told me he thought a similar-sized unit to the rental-space furnace (80,000 BTUs) would be slightly undersized, it's got me wondering what to believe.

I've been consistent with my numbers that were input into the online calculators. Another consideration for the shop space is, along the back wall there is a mezzanine 8' off the main shop floor that juts-out 8' from tieback wall. I suppose there'll need to be some ducting done to direct air above and below the mezzanine, but perhaps that's a personal preference on my part.

What are the proper guidelines for sizing the furnace to my space?

Thanks for the time!

 
PJmax's Avatar
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01-27-17, 06:14 PM   #4 (permalink)  
I don't sell.... I just service so I don't get involved much in sizing the units.

If my calculations are correct..... based on a heat rise of 25 degrees you'd need 450k btu of heat.
The problem here is the 18' ceiling plays havoc with the square footage of your garage.
The ceiling fans will definitely be a plus as you're heating an awful lot of ceiling.

The plus to a regular floor furnace is that you can run the duct work where it's needed.

Based on a single point heat source..... that 125k btu unit may be just what you need.


~ Pete ~

 
gloveguy's Avatar
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01-27-17, 08:02 PM   #5 (permalink)  
May I ask what you mean by "single point heat source?"

I know you said you don't get into sizing furnaces much, but with your calculations (not holding you to it) and my furnace tech indicating that 80,000 BTUs being "slightly" too small, there's an obvious science to the sizing side of things, which I kind of figured going in.

Between 450,000 BTUs and 125,000 BTUs (the used unit on CL) that's quite a gap, isn't it?

I still may go look at this used unit, but I'm finding the research interesting anyway.

Thanks again!


Last edited by gloveguy; 01-27-17 at 09:03 PM.
 
PJmax's Avatar
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01-27-17, 09:25 PM   #6 (permalink)  
I played with several different calculations and the heat rise figure makes the largest change.
My original figure was based on no insulation.

Try this calculator. It looks like 80K is a little on the small side.

btu-calculator


~ Pete ~

 
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03-27-17, 12:42 AM   #7 (permalink)  
I have had pretty positive experience. However, my brother in law helped me. We went over to the seller's place and examined the heater. My brother in law (Simon) works in the industry and even brought his thermal analysis tools along to properly examine if the gas heater was any good. I would always always recommend you to bring someone along that knows what they are doing!


Last edited by Gunguy45; 03-27-17 at 03:11 AM. Reason: removed link as possible advertising
 
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03-27-17, 05:15 PM   #8 (permalink)  
Heating a shop, especially a shop used intermittently, is a bit different than heating a residence. You want to heat the shop quickly and temperature excursions of three or four degrees are generally acceptable. For these reasons I suggest a heater/furnace significantly larger than a heat loss calculation would come up with.

With the tall ceilings I would run the return-air duct high and keep the supply ducts fairly low. Do NOT skimp on the size of the ducts as you want to move as much air as possible. You can also use the different speeds on the blower to advantage to both heat faster and maintain the temperature in a more satisfactory manner.

 
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