How many BTUs

[44 massey]

Thinking about replacing the hanging forced air propane heater in my shop!!! My shop is a 30 x 50 x 14 insulated metal pole building! The old furnace had a a rating input of 150,000 BTUs and output of 120,000!! When getting bids on new furnace they are telling me that with todays furnaces that a furnace with a 105,000 BTUs input and 80,000 BTUs output will be plenty big enough!! When the old furnace was working good I could turn it on at 7:00 in the morning in -30 weather (20-30 inside shop) and it would be 55-60 by 8:00-8:30!! My thinking is Id rather it be too big then not big enough, winters get cold in ne Nebraska!!

 

[Geo-TH,In]

The garage I recently sold was 26x44x16,
There is one big problem, heat rises.
I could measure 100 degrees on the ceiling and snow on the floor wouldn't melt.
I discovered you can't push hot air down, instead you need to push the cold air up to the heater on the ceiling.

My heater was in the corner, so we took a squirrel cage fan on the floor and pushed the cold air up the corner towards the heater. Try it and let us know if that helps.

If you are not heating 24/7, yes going bigger is better.

 

[Moonlite37]

I did not know that!

 

[TomIn]

An engineer neighbor of mine once told me that HVAC was the most over-engineered part of most construction jobs. Your goal should be to deliver enough BTU's to the area of your building you will be occupying to make you happy. A BTU output has always been a BTU output--regardless of how it was created. George is correct in saying that heat rises and that the air temperature will tend to be higher at ceiling level. Air circulation can minimize this problem, but air movement will tend to make you feel colder. George's solution of is one way to keep the strongest part of the draft from blowing on you while you are working. If you use ceiling fans, they are generally used to move the air upward in the winter so that the strongest draft is along the ceiling rather than where you are standing on the floor.

It is impossible to predict the necessary BTU output from the limited information you have provided. My pole barn is insulated to some degree by a layer of dust on the underside of the roof and the walls. Yours is likely better insulated, but you don't say how well. As George said, you didn't indicate how frequently you heated the shop.

You mention that a dealer has recommended a 105,000 BTU input furnace that has an output of 80,000 BTU. I'm a geezer who hasn't paid much attention to energy efficiency standards for the last decade or so, but I recall that 80% efficiency has been the minimum standard for northern states for many years. It sounds like the dealer is trying to sell you the least efficient furnace on the market --hopefully to justify a lower price than his competition. If you want to save money on fuel costs, consider a higher efficiency furnace or perhaps an infrared radiant heating system. A HVAC professional once told me that you can save a lot of money, as long as you don't care how much it costs.

 

[moresmoke]

If you routinely want to go from cold shop to warm, go larger than the recommended size.

 

[Richard G.]

George, that makes sense.
I have always heard that a ceiling fan reversed to push the air up and move the warm air down the walls is the way to do it.
Richard

 

[showcrop]

I agree with Tom that the bids you are getting is for a standard set back of 20 degrees or so instead of shutting off and starting over. My shop is 40x50x17 with 6 inches and 9 inches of insulation. I have a 16'x22'x10' "inner room" where I do 90% of my work in the winter. I keep it at 50 degrees and then bump it up to 65 when I go in. It is heated by a little non-vented catalytic heater. When I need to heat the rest of the building I turn a larger unit on.

 

[Randyscottsboro]

I don't care about BTU's just one that will keep my BUT warm.

 

[Geo-TH,In]

What about checking into a condensing furnace. Closer to floor or hanging it. Pulling the cold air off the floor. Greater efficiency.

 

[Janicholson]

A condensing Furnace with 95% thermal efficiency is way better for this application. To get from Cold to operational, I would want a 150,000 BTU output. Pulling cold air from the floor and directing it down from the top to the work space is optimal. A better efficiency will pay off ever more rapidly as fuel gas prices increase. Jim

 

[GordoSD]

My shouse is 40x 72x12. I have a 2000 propane Reznor 150 BTU hanging unit. I keep the shop part at 38 degrees. Bring it up to working temp of 55 degrees in about 25 minutes.
6 inches Insulated bats in outside steel and inside wood. Insulated doors and windows. I have the local insulated ovhd door man Rusty come out every Oct and make those doors tighter than a tick, seals, gaskets and all. Those doors get opened maybe once every 5 days. (for a few seconds LOL)
I use right at 400 gals PP over the winter and I am 200 miles north of you. (Mitchell)
Go with the 150 BTU Output unit and don't lets it get so cold overnight. You are cold soaking floors, walls, vehicles, whatevers in there.

 

[OH Boy]

Unless you are going to keep the building constantly heated, do not go with a condensing furnace, they produce and hold water inside of them. That water will freeze if you turn the heat off and temp drops below freeing.

 

[atlarge54]

Does a condensing furnace and the associated drain system need protection from freezing?

 

[the tractor vet]

Well i am not up on all the new ways of heating a shop or how much ya need . what my buddy and i had was a 40x72x13.6 with about two inches of spray on insulation . the big heat loss was the sliding doors . In the far back corner sat and old 24 inch coal furnace and a ten dollar box fan . From the onset of days dipping down into the 50 during the day and 30's at night the fire was built and with out to much trouble and about and hour and a half i could take it from 50 degrees and have it roasty toasty 72-75 short sleeve comfy and we would burn around one ton a month . even back during the blizzards of 77 and 78 when we saw what some of you boys see regularly down into the -30's the shop was in the seventys . We would bank the furnace at night and shut the fan off and i don't care how cold it got inside never went below 50 even if we left it for a couple days with out lighting the furnace . For us Coal was the Only way to heat ------ since we were both hauling coal at the time and we were getting some of the best coal one could find in our area and that was Pittsburgh #8 . When he and i would go load at this one stripping operation We would tell the loader operator that we needed some of the PRIVET stock for heating . and what that was was coal from arouud the edges of the huge pile the larger chunks , Bob the loader operator would run around the pile when he had time anc clean up the bigger chunks rolling down the outside off the convair belt and build a pile for the ones wanting house coal as everything went to power plants and they did not want big chunks . Normally when loading we would load two loader buckets in the nose and two back by the tail gate and then one and a half in the middle and another full bucket placed the full length of the trailer as we pulled out usually giving us between 40-45 ton per load . when loading our SHOP coal he would dump two in the nose two in the middle and with the corner of the bucket fill the back end by the gate with the stove to lump size coal there then add a full bucket from the nose back almost to the lumpy stuff . We would then take the load home and once at the shop trip our gates and dump off the lumpy stuff close the gate then raise the bed up and level the load . next morning at 3Am we were off to Toledo to one of the power plants out that way with usually a 40-42 ton load and we had our winter supply of coal . It was a nice warm even heat . The other heat that seamed to work good were the Ray- o- vac. or tube heat and now the floor heat seams to be taking over . a couple local guys that hit big with there gas leases that needed to DUMP a bunch of money rather then give it to the gov . Built new dream shops and went with the infloor heat and heat BIg play rooms with two 80 gal. gas hot water heaters and keeping them at 72 degrees 24-7 . Now yes the gas is Free to them off the first wells that were drilled on them some oh gees 40 years ago on the Clinton push as back then everybody that got a gas well drilled got somuch free gas per year when the came in here a few years back they were HOGS and you did not get the free gas claws in your lease . Now that shop heat is nice and even and if ya got cold feet not no more while in the shop working .

 

[Roger Tomfohrde]

A couple thoughts;
-80000 divided by 105000 = 77% eff or a furnace with a steel non condensing vent.
-If intended use is for just getting it warm to work in during a day or so, use the specifications of what you have.
- If you are going to maintain a minimum temperature in the area, go to the smaller specified unit as the amount you need to raise the temp is not as much.
--Newer units they want it to cycle around four times every hour to maintain the heat exchanger integrity.

 

[Gary Mitchell]

I enjoy your writing TV. You may have missed your calling. gm ;-)

 

[Janicholson]

The furnace heat exchanger on modern condensing furnaces are kept water free using a drain. Mine was originally piped through 2
PVC up an existing chimney. The chimney was condensing the water and created a runback situation. The installer put a float valve
pump at the furnace to pump condensate into the laundry tub drain. I rerouted the intake/exhaust to the side of the house through
the wall (the original kept getting birds down it, a different story) because the new exhaust pipe was only 10 ft long, the
condensate went out with the exhaust pipe and the pump has never restarted. By the way the PH of the condensate is close to 5.
That is corrosive, and needs to be dealt with outside, not used to water plants. Jim

 

[MT pockets]

I had rather read Tractor Vet's writings than to eat ice cream. Steve in Banner, Ms.

 

[Hobo,NC]

Stay with what you had if it worked... For me it would be a tad to much...

 

[Blackhole49]

You should price out a radiant tube heater. Much more efficient. I have 1 in each barn. The big barn (30x48x12) is uninsulated and it will still get to 60 in 0 weather. Once up to 60 the small insulated barn (24x40x8) will stay there and the furnace will only run a few times a day (I keep it at 45 when I'm not in there). When I installed the units in 2002, they added about $300 to my natural gas budget.

 

[Hobo,NC]

I often wonder why you don't see talk about radiant tube heat. The local GM dealer had it in their old shop for years they just built a new shop and put radiant tube heater's in it. The shop guys love it.

A bud put it in his home shop I need to ask how its working.

 

[Blackhole49]

The nice part about radiant tubes is they heat the floor also and are made for high bays. I have to be careful what i store under the heater in the 8' barn.

 

[Determined]

Here is a higher versus lower BTU comparison that may help you decide.

Our house has a 100 000 BTU furnace.

Our son's house same size same area has a 60 000 BTU furnace.

Both houses are well insulated and our propane usage is very similar.

Differences;

When our furnace runs the air from the vents is noticeably warmer and the run time to bring the house up to the set temperature is usually quite short. 8-12 minutes.

When our son's furnace runs the air from the vents is noticeably cooler than ours and accordingly his run time is much longer per cycle. average 20+ minutes.

Basically our 100 000 is like a big V-8 truck, it uses lots of fuel but it gets the job done fast.

His 60 000 is like a fuel efficient little 4 cylinder truck, it gets the same job done but because it can't do it as fast the amount of fuel used is very comparable.

If your shop is kept at a constant temperature the lower BTU unit will suffice.

If you turn the temperature down when not using the shop and you want to be able to bring the temperature up to a comfortable setting quickly then the higher BTU unit will serve you better.

Regarding moving heat down from the ceiling I have a piece of six inch stove pipe about 10 foot long with an inline fan mounted in the top of it.

The end with the fan is close to the ceiling, the bottom end has a simple piece of cardboard attached to deflect the flow along the floor.

When I bring in a vehicle it can sit overnight and still have ice on the bottom of it.

If I run the stovepipe fan by morning the ice is not only gone but the floor is dry as well.