Sizing a furnace

Shop 40'X56'-10 ft. ceiling. R38 in metal ceiling,R19 in the metal walls. Have been given a 2 yr old 80% efficient ,70,000 btu input.Don't think it is big enough for Indiana. What say you ? Have been advised against a radiant tube by the dealer. In floor heat is not an option.TIA,bob

I think you would need 120,000 btus to be effective. I have a 2500 sq. foot home and a pellet burner that is for a 1400sq foot home, I think it is a 60K btu. When the outside air gets to below 15f the pellet burner cant keep temp above 68F.

I would use that furnace and then get a used wood burner and then you would be all set, or get a small kerosene heater.

ASSUMING you won't have a big door open a lot and need lots of recovery, that furnace WILL do the job.

Probably not as big as would be recommended, but for FREE what have you got to lose trying it?

I'd agree that's too small, especially most shops need quick warm up and fast recovery when doors have been opened, etc, so normal sizing does not so much apply. How are you going to configure this? Can you make use of this freebie? You might put it in one corner, or use it to heat the "office space" if applicable, and then hang another small unit heater, say, about the same size, out in the opposite corner. That should give you more even heat, and if one quits, you still have some heat.

What is this thing and how do you plan to "hang" it? Upflow, downflow/ horizontal? You plan on any ductwork except for a basic bonnet and couple of diverters?

As they say on the other forum, you should be pretty close. Depends how hot you want to get it in there, and if you have a door open a lot. I'd think you would have about enough?

--->Paul

They make curtians so a person can zone off areas to be heated ,as you really don't need to keep the entire building heated do you .

Can you get another one for cheap? Both together should work just fine.

Vito

my shop here that I use for my business is about the same size but I have 8' ceilings. It is a block building and even though the blocks are filled with insulation I think a building insulated like yours would be easier to heat. I use a 100,000 btu corn burner at 60 degrees and its plenty here in PA. If your going to be working very hard 55 degrees would be plenty warm IMHO, as my 60 degrees can be too warm sometimes.

MSB, I have two buildings one is 40 by 100 and heat it with two 20 ft. infra-red heaters and they will burn you out if you set them to high,and vary cheap to operate. Have had them for twenty + years and NEVER had a problem with eather one. Also use one in my home shop 32X40 and it's the same with that one too.Best thing I ever did...HTH...Jim in N M

yeah and kerosene in KS is 17.99 ON SALE for a 2.5 gal jug....how would that help? What does it cost in INDIANA?????

I don't see a mention of windows and doors. How many, quality, and how well sealed against wind?

7x16 garage door, 3' walk door and 4 single pane windows.Will install second windows inside. Menard pole barn package, well sealed up.

It's a little small. I have a Modine hanging one about that size in a tight 30X32 shop that's insulated about like yours and it's ample but your shop has a lot more square feet than mine.

The furnace you have is next to new but it still sends up a red flag to me. When I built my shop I was given a gas furnace from a house that was maybe 20 years old so I installed it in the new shop. A year later I went into the shop one morning and it was foggy and hot in there and back in the corner by the furnace I saw flames shooting maybe five feet in the air. I couldn't run fast enough to get to the gas tank to shut the valve. The line going to the pilot light had cracked and the leaking gas ignited. I keep a clean shop so there was nothing by the furnace to catch fire, but it really tested my blood pressure. Insurance paid enough for another used furnace but I wasn't about to take the chance with another used one. I spent the extra money to have a new hanging furnace professionally installed.

I am told the insurance companies like the hanging furnaces better because they're above the heavy gas fumes that might be lurking near the floor of a shop. The water heater in the shop is up on a platform six feet off the floor for that reason. Just something to think about. I wish my shop was as big as yours. Jim

(quoted from post at 19:44:15 12/04/09)
The furnace you have is next to new but it still sends up a red flag to me...................... I was given a gas furnace from a house that was maybe 20 years old................. I went into the shop one morning and it was foggy and hot in there and back in the corner by the furnace I saw flames shooting maybe five feet in the air.

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I dont see this as a comparison. ANY combustion appliance should see regular maintenance / inspection, something a lot of "you types" on here seem to just hate. Used to be my JOB and I found a lot of potentially dangerous situations. I've seen 5 year old furnaces with cracked (dangerous) heat exchangers, and others nearly 40 years old, that with a gas valve update, were good to go.

Also, just because it's a "furnace" does not mean it needs to be on the floor. You could install a downflow/ horizontal on the ceiling, configured much like a hanging unit heater. A standard upflow used to have to have the burner 18" above floor level, but you could hang it halfway up the wall if you wanted to.

One thing you REALLY want to be aware of is such things as shop welding exhaust hoods or homeshop paint booths---anything with a sizeable exhaust fan. This will cause a massive vacuum in the shop, and will cause vents to revert. Many modern furnaces/ heaters have protection known as "vent spill switches" and they can be installed after the fact.

One other caveat about using a duct furnace as a unit heater with little ductwork. When a furnace blower is devoid of ductwork, it "overamps" the motor. Some units with multi-tap motors can be slowed down with good effect, others, with oversized blowers, need a minimal amount of ductwork/ bonnet to actually restrict airflow and tame down the blower.

A lot depends on how warm you need the shop. Are you a commercial shop with customers coming in? Do you like to work in short sleeves or overalls? Are you in it everyday and allday or just certain times on certain days? Are you laying on your back on a creeper on a cold concrete floor while under a vehicle? I'd sure want a vent close by if close to the floor.

At least get a setback thermostat to have it warm when you get there. Size the plenum and ductwork appropriately for the size of the air handler and at least aim the vents where you will be working to get the max benefit when it is on about all the time. If you have the plenum and ducts sized right, then if you upgrade maybe you won't have to change them. At worst maybe only change the plenum with a new one.

I've worked in some freezing buildings and it helps a little to have some hot air blowing on you.

What about A/C for the summer? Better plan all that now.

Kerosene in Michigan is $4.10/gallon, thats why I mentioned the wood burner too,