Best way to heat your garage?

[Foose911]

I live in Northern Canada and have to heat my 22' x 24' unfinished detached garage that has a 12' ceiling with closed rafters. It has a 16' aluminum door that I'm planning to insulate with foam panels, otherwise it has standard insulation (r20 walls, r40 roof). I need it above +18 C (64 F) during the day for auto painting. It gets as cold as -40 C (-40 F) here and it takes a long time to heat the garage even when it's above freezing.

OK, for the smart people on this forum, my basic question is this:

If I keep the garage at +18 all the time, the 45,000 BTU gas heater will come on for a few minutes every so often. If I switch it off overnight and re-warm it in the morning, the heater seems to be on continuously for maybe half an hour. So, given the specs, what way is most efficient for me? How do I even go about figuring it out?

 

[tcccac]

Not sure if it is the "best" solution but I plan on using a pellet stove set on low as the primary with a 75,000 btu propane heater as the backup.

 

[CNGsaves]

Since you've got NG heater that by design heats quickly (you say it runs about an hour if switched off overnight), then likely lowest cost method is turn off overnight. Then turn on heat about AN HOUR EARLY from when you want to be in shop.

Heating all night and other times that you are not in shop is "wasted" heat, unless you want some minimal heat in there to keep things from freezing. Some people have low temp T-stat that maintains shop at 40 degrees F.

Some HVAC gurus might chime in that T-stat could automate your turn-on and turn-off procedure to minimize cost.

 

[sourdough]

I live in Northern Canada and have to heat my 22' x 24' unfinished detached garage that has a 12' ceiling with closed rafters. It has a 16' aluminum door that I'm planning to insulate with foam panels, otherwise it has standard insulation (r20 walls, r40 roof). I need it above +18 C (64 F) during the day for auto painting. It gets as cold as -40 C (-40 F) here and it takes a long time to heat the garage even when it's above freezing.

OK, for the smart people on this forum, my basic question is this:

If I keep the garage at +18 all the time, the 45,000 BTU gas heater will come on for a few minutes every so often. If I switch it off overnight and re-warm it in the morning, the heater seems to be on continuously for maybe half an hour. So, given the specs, what way is most efficient for me? How do I even go about figuring it out?

IMO, it matters not if you do a night setback if you are in and out of the garage every day resetting the t-stat. If you leave the garage at the lower t-stat setting for several days at a time, you will save fuel. Otherwise, savings are negligible to non-existant.

If it matters, I lived in South-Central Alaska for 34 years and have relocated to milder climes in my retirement. Getting old and not so fond of 6-month winters.

 

[Foose911]

Thanks for the replies so far, but I'm still confused.

A pellet stove sounds like a good idea if I had one ... I think it would cut down of fuel costs and doesn't take much space.

The heater runs for approx. half an hour in the morning now (+5 C), but I think it will be on much longer when it gets cold.

SOURDOUGH: I'm opening and closing the small door every 20 min or so when I'm painting. Is my best bet to keep it heated during work days and turn it off completely over the weekends?

 

[bzinsky]

There is a common misconception that it costs more to let something cool down and then heat back up then it does to maintain heat. Same with cooling.

Temperature differential = money

The difference between the outside and the inside is what determines how fast you will lose heat, or money. (that and R value). The longer you let that space sit closer to outside air temps the more you will save. It will always be cheaper to turn the system off, no matter how short of time, there are very few exceptions to this rule.

 

[CNGsaves]

There is a common misconception that it costs more to let something cool down and then heat back up then it does to maintain heat. Same with cooling.

Temperature differential = money

The difference between the outside and the inside is what determines how fast you will lose heat, or money. (that and R value). The longer you let that space sit closer to outside air temps the more you will save. It will always be cheaper to turn the system off, no matter how short of time, there are very few exceptions to this rule.

^ ^ Generally true. Exception to above bold section might be Heat Pump as it simply doesn't have oooommmph to raise temp quickly. Thus, a heat pump will work better if kept within swing temp range of say 4 or 5 degrees.

OP has Natural Gas heat so I say it will be cheaper to shutdown and restart, especially if sporadic use of garage.

Maintaining a minimum temp is his personal call (ie prevent freezing, or keep vehicle little warmer for easy starts).

 

[bczygan]

Easy to test it by taking meter readings at set times using each method.

 

[Foose911]

Easy to test it by taking meter readings at set times using each method.

That would save a lot of theory, yes. I'll do the experiment!

 

[bzinsky]

Easy to test it by taking meter readings at set times using each method.

Its not necessary.

As for heat pumps, they substantially increase efficiency when outdoor temps are higher. So it may be best if you let the heat pump only operate when you are working, which is likely during the day when the temps are warmer.

Always turn the heater down when your not in there.

Try not to look at your heater firing up as wasting money. The heat leaving your building is money leaving the building. Heat is energy, no matter how you slice it, when heat is dissapating to the outside, your heater has to replace it. If you let your garage cool to 40 degrees at night, there will be a lot less heat escaping.

 

[finn]

I seem to remember from my heat transfer classes in the last century that heat transfer is a function of delta T, so the greater the difference between the inside and outside temperature, the more heat will transfer out of the building into the atmosphere.

Also, most furnace operate at their highest efficiency at maximum output.

Shut the heater down at night.

 

[Foose911]

Garage door is now insulated (cost me less than $200) and I bought a new programmable T-stat that can be programmed for each day. Seems like I'll save money by programming it to switch on an hour before I start and turn off after 8 hours, allowing the garage cool with no maintenance heating. Thanks everyone!

 

[plott hound]

put a hi-eff furnace in your shop.it will be way more efficient then the unit heater.leave the stat set at 50 when your not there,bump it up when you go in there to work.

 

[theoldwizard1]

With your existing furnace and maintaining a constant temp, I don't think you can improve your fuel usage.

The cheapest way to save on fuel is an automatic set back thermostat. One that turns the temp down to about 10C from midnight until sometime in the AM. Or just leave it at 10C, until you want to work in there.

 

[bzinsky]

I seem to remember from my heat transfer classes in the last century that heat transfer is a function of delta T, so the greater the difference between the inside and outside temperature, the more heat will transfer out of the building into the atmosphere.

Also, most furnace operate at their highest efficiency at maximum output.

Shut the heater down at night.

yes that is absolutely correct, I live by that and it has saved me a ton of money.

Most heaters don't adjust their flame, they just are on and off.

The only thing that we can adjust is water temp if it's a boiler. Lower water temps are more efficient because of the same principal. The colder water will absorb more heat from the flame.

This is the basis behind why radiant floor heat can be very efficient. You are heating up a huge surface area and it allows you to keep water temps low, around 120 degrees. On top of that, it feels good on your feet and doesn't take up any space in your house.

Radiant floor heat in a garage is sort of a bad idea, because you are not maintaining that heat 24/7. You pay all this money to heat up this giant concrete slab of thermal mass, and you reap the benefits of thermal mass at night and the next day, when you're not even in there.

I think another good principal to understand is that thermal mass does not mean you are saving money. A castle with 5 foot thick walls would not be any cheaper to heat than probably a modern wall with r13. The stone walls certainly hold a lot of energy, but just because it takes 2 weeks for heat to get from one side of the wall to the other, doesn't mean it's actually cheaper, it's just delaying the heat loss for 2 weeks, and it feels like you're heater is operating less.

The real benefit to thermal mass is for AC. It allows you to delay the warming of your house during high temperatures, and then you will be playing catch up at night. At night time it's cooler out and your AC will be operating far more efficiently.

R-value is the most important thing, and it is what stops heat transfer. Heating up a concrete floor does not save any money, especially in a garage that doesn't need heat at night and is only used on a temporary basis. Infact it's probably wasting a lot of money. On top of that, it's a complicated system.

The best way to heat a garage is a good ol gas forced air furnace. They are cheap, can be very simple, and it heats up fast and shuts down instantly. You're not heating the place when you're not in there and you can heat it on demand with only a half hour of warm up. Even if you installed radiators, you shut it down when you walk out, you still paid to heat that water up which is still heating the garage as you leave.

 

[Denwood]

What they said. Simple answer. Minimize your BTU input and your savings will be greatest. Set back when you leave, turn up when you arrive. That will reduce your consumption the most. No need to test this. NRC and CMHC (in Canada) has already done your research.

If you work regular hours and want the shop at temp when you arrive, a smart thermostat like Ecobee will maximize your setback times based on current weather, wind, sun, and forecast. It also "learns" recovery times for your building, and adjusts accordingly, again to maximize set back times. As it is wifi connected, you can also adjust manually and review energy usage via the web portal.

I worked with our architect and engineers on Cinevate's new home..a warehouse gut/retrofit with tenant, production, office, shipping areas added. With temps last winter dropping below -20C over 60 days, our largest gas bill was $242...to heat 9500 sq/ft This includes a loading bay with 20 ft ceilings and 10'x14' overhead door. Hard to believe, but I have our bill history in pdf format to prove it. We took video over the entire project which basically was a very thoughtful building envelope efficiency program.