I'm Overthinking the Heater Situation

[jethead102]

Hey all, long time lurker and have really enjoyed this site!

Recently moved and need to install a heater in the garage. Chicago area. Old house came with a gas 45-50k BTU heater, I kept it at 40 all winter long and when I wanted to work on the cars or anything it would easily and quickly get up to whatever temp I wanted (just for fun, I tried 80 degrees on a day when it was 10 out, and it worked). I was spoiled by that, though I believe that unit was oversized for a two car. I'm having a hard time deciding between the various options for the new place.

20x30x9.5' three car with 30 feet of wall attached to the house. Currently 35' of uninsualted walls and ceiling is uninsulated, but fixing all that is one of my winter projects when I put in new shelving and such. Garage doors are foam insulated. I'm considering:

1. 2x 5,000w electric heaters placed in opposing corners
2. 1x 7,500w electric heater placed angularly in the coldest corner, blowing between the garage doors
3. 1x 50k BTU gas heater, placed angularly in the coldest corner, blowing between the garage doors, vented horizontally

Again, I'll be warming it up to 60 or so 2-3x/week, and keeping it at 40 for all other days in the winter. Thermostat will be near house door. Will the electric units be undersized or run too often? I realize the acquisition cost difference, but it'll take me about 4 years to break even on the operating costs (and the price of gas is only liable to go up). I'll be installing myself, hence the overanalysis. I appreciate any insight!

 

[cadunkle]

I'm no pro, but as it sits the electric will cost a fortune and is not viable uninsulated, but you know that. Once insulated 10k watts of electric should be adequate, but but will cost a lot more to run.

If you have gas on the property already, that's the best option. Cheaper to operate, and the ~50k BTU unit heaters are not too expensive.

For reference:
7,500w = 25,591 BTU
10,000w = 34,121 BTU

45k BTU gas at 80% = 36 BTU heat
50k BTU gas at 80% = 40k BTU heat

I pay $1.409305/therm and $0.148653/KWh. Comparing electric heat to NG, electric cost about 2.5x as much to run for the same BTU output. Your use case at 40*/60* differs from mine, so ROI will differ. I've done my time working outside on dirt and in the snow and now I use a 45k BTU NG heater for 720sf with 10' ceilings, maintaining 60* unoccupied and 72* when I'm out there. The heater costs $0.63/hr to run, under an hour to temp and with an insulated space doesn't cycle much once up to temp. 36k BTU of electric to get the same result would costs $1.57/hr. Purely on BTU, if you don't open the doors much 10k watts of electric will get the job done, but gas is better and if I had to do mine again I'd go larger for a faster recovery when opening doors.

 

[D45]

50k btu gas

 

[PoorUB]

15,000 BTU should heat it. That is one 5KW electric, or a 30,000 BTU gas.

50,000 BTU gas is way too large, the 30,000 BTU gas I recommend is large, but the smallest you see in a typical garage heater.
My neighbor heats a detached 24x36 garage with a 30,000 BTU Modine Hotdawg.

Here in North Dakota I would not hesitate to put the 5K electric or a 30,000 BTU gas.

Keep in mind you don't need to heat one wall.

Gas is generally less money to operate.

 

[theoldwizard1]

In most parts of the country, the cost to run electric resistant heat is significantly higher than any other energy. It is the cheapest and easiest to install.

Modern mini-split heat pumps are very efficient, probably better than all other alternatives, but it is this most expensive to install.

 

[u3b3rg33k]

You're in the midwest, so you know it's humid in the summer. why is a 12-24k minisplit not on the list?

5kW electric gets my (almost done) fully insulated 2 car garage up to 70F in single digit weather, north of you.

 

[Scooter Scott]

I just overthought mine and ended up with a 7500W electric for right now. I'll see how much I can bare the cost of heating the garage after I insulate it. I have gas on my property and do want to run it....I just have no good places to mount the heater due to my garage being at the front of the house and I can't think of a place that I would want a 2ft exhaust pipe sticking out the side.

 

[jethead102]

All good thoughts, I appreciate the insights. Ideally I'd get something like a 30k gas heater, however they're twice the price of the 50k. I'll appreciate the faster time to warm up as well. Factoring in the cost of copper, the electric heaters are still cheaper to acquire, however only by a few hundred dollars. I'm going gas.

Thanks again! I'll follow up when completed.

 

[PoorUB]

So you are going to buy a heater that is 4 times too large instead of one that is 2 times to large for the space?

 

[jethead102]

No, I'm proiritizing time over pure metrics. When I want it warmed up or a garage door has to be opened up really quick, I don't want to have to wait an hour, nor do I want to think about the $1.50/hour electric just for putzing around in the garage when I'm doing that (which is frequent). I'd gladly get a 30k gas heater, but the acquisition cost is twice that of the 50k; unless I missed something in my research, they're only online and in the $900 range. The 50k is on sale for $400 at a local farm store.

I'll (hopefully) be in the house for 10+ years, so the operating efficiencies of the gas are also attractive. It never fails that the moment I get the garage to a comfortable temp, my wife has to leave or gets home and opens the garage door...

Does anyone have good insight to actual recovery times and time to warm up, say on a 20* day to take an insulated garage from 40 to 60? 5k and 7.5k watt electric

 

[PoorUB]

The properly sized heater at $500 more, amortized over a 15 year life span is $35 a year, and it might run 20 years.

I will bet a 50,000 BTU heater will not last ten years because the heat exchanger will rot out. So you get to replace it again.

Which is a better deal??

 

[cadunkle]

Does anyone have good insight to actual recovery times and time to warm up, say on a 20* day to take an insulated garage from 40 to 60? 5k and 7.5k watt electric

720sf with 10' ceilings, R13 walls and R22 ceiling, insulated doors, 45k BTU. I timed mine at 50 minutes for a 12* temp rise (60*-72*), outside temp was likely 35*-45* at the time.

I also have (I think) about 1750 watts of electric baseboard heat in there. **Running full tilt with temps around freezing those can maintain around 60* inside. It'll take hours or days to get the temp up though, and don't open a door for more than a few seconds it's lost and will take hours to warm up. It doesn't take much to make a space tolerable if it's reasonably well insulated and sealed, but for those of us that like warmer temps it won't be comfortable.

I suspect the difference of opinion or preference on sizing from minimal acceptable for a space to oversized vs a living space may be personal tolerance to cold. I can be comfortable in a 60* space but if it was 40* not long ago my feet and hands will be eternally cold on the cold slab, tools, and vehicles or parts. I'll take 95* and humid over working in the cold, and will be happy sweating all day. Others are the opposite.

**Edit: I was mistaken, full tilt the 1750w electric will go past 60* but takes a long time. I had the electric heat on last night but thermostats reset back to 50* (I thought I left them on manual). Waiting on a replacement gas valve for my unit heater. In any event, I turned the ~1750w electric heat on manual two hours ago and the temp has increased 4*. 64* is ok with a warm shirt and a winter hat, certainly beats 40* outside. Maybe it'll hit 72* after I go to sleep. I'll leave them on manual until the gas valve arrives, I don't want to plan 6-8 hours ahead for when I want to do anything. The thing that ***** is I need to paint a bunch of parts this week. Normally I'd open the man door and crack the rollup door for ventilation, the unit heater keeps up and allows ventilation.

 

[u3b3rg33k]

No, I'm proiritizing time over pure metrics. When I want it warmed up or a garage door has to be opened up really quick, I don't want to have to wait an hour, nor do I want to think about the $1.50/hour electric just for putzing around in the garage when I'm doing that (which is frequent). I'd gladly get a 30k gas heater, but the acquisition cost is twice that of the 50k; unless I missed something in my research, they're only online and in the $900 range. The 50k is on sale for $400 at a local farm store.

I'll (hopefully) be in the house for 10+ years, so the operating efficiencies of the gas are also attractive. It never fails that the moment I get the garage to a comfortable temp, my wife has to leave or gets home and opens the garage door...

Does anyone have good insight to actual recovery times and time to warm up, say on a 20* day to take an insulated garage from 40 to 60? 5k and 7.5k watt electric

these times aren't what you think they are. with a 70F garage that's been 70F for a while, everything in there is actually 70F.
so when you open the door, pull your car in, and close it, you really only have to re-heat the volume of air, not the thermal mass of your stuff.

just think about how long it takes your engine block to heat up. that's got a gas fire going on inside and it still takes 5-10 min to get warmed up. now pull up to the store in your warm car, go inside, buy a 6 pack, and come back out. it doesn't take another 10 minutes to warm up the car again.

 

[theoldwizard1]

I just overthought mine and ended up with a 7500W electric for right now. I'll see how much I can bare the cost of heating the garage after I insulate it

Insulation and the number of heating hours make a HUGE difference.

 

[theoldwizard1]

No, I'm proiritizing time over pure metrics. When I want it warmed up or a garage door has to be opened up really quick, I don't want to have to wait an hour, nor do I want to think about the $1.50/hour electric just for putzing around in the garage when I'm doing that (which is frequent)

My Dad had a place in northern MI. It had old fashioned wood burner (looked like a standalone oil burner) and access to all the wood you could want. When the temp was in the single digits and the wind was blowing, one side of you was melting and the other side was freezing (no insulation).

 

[toyotadriver]

I heat my attached garage at times with a 45k propane heater. It's a little smaller than the OP's but not by much. A bit warmer climate than the OP's climate but can still get cold in the winter. A 30k would be ideal for me but I already had the 45k so it made sense to just use it. So far, it's been there for 5 years and no signs of rusting or any other issues.

Getting a thermostat that can have a wider swing temp can help with any fears of condensation in the heater in a heater that might be a little oversized. A large swing temp isn't ideal inside a house but in a shop you're working in, it's not an issue. It'll run longer and then be off longer between cycles.

 

[PoorUB]

The heat exchangers rust from the inside out. They look fine, then one day there are shot.

 

[jethead102]

Alright, y'all talked me off the ledge. Oversized gas is out, and right sized gas will take many moons to break even. I redid all my math, and at this point I really don't care about the break even.

I'm down to one 7500w electric or two 5000w electrics in opposing corners. Walls will be r-13 and ceiling r-30 or so. 2 inch insulated garage doors. Again, Chicago area. Acquision cost difference between the options is relatively negligible. Thoughs on sizing? 34k BTU or 25k BTU? Obviously it's impossible to short cycle an electric heater, so the quicker warm-up time would be nice with the 34k.

 

[PoorUB]

Put in one 5K. If you are not satisfied, put in a second 5K.

My bet, as long as the place is properly insulated the 5kK will be all you need.

 

[ShopNotShed]

I'm no pro, but as it sits the electric will cost a fortune and is not viable uninsulated, but you know that. Once insulated 10k watts of electric should be adequate, but but will cost a lot more to run.

If you have gas on the property already, that's the best option. Cheaper to operate, and the ~50k BTU unit heaters are not too expensive.

For reference:
7,500w = 25,591 BTU
10,000w = 34,121 BTU

45k BTU gas at 80% = 36 BTU heat
50k BTU gas at 80% = 40k BTU heat

I pay $1.409305/therm and $0.148653/KWh. Comparing electric heat to NG, electric cost about 2.5x as much to run for the same BTU output. Your use case at 40*/60* differs from mine, so ROI will differ. I've done my time working outside on dirt and in the snow and now I use a 45k BTU NG heater for 720sf with 10' ceilings, maintaining 60* unoccupied and 72* when I'm out there. The heater costs $0.63/hr to run, under an hour to temp and with an insulated space doesn't cycle much once up to temp. 36k BTU of electric to get the same result would costs $1.57/hr. Purely on BTU, if you don't open the doors much 10k watts of electric will get the job done, but gas is better and if I had to do mine again I'd go larger for a faster recovery when opening doors.

How do you get these figures? Thanks for the info, super useful!

 

[cadunkle]

My notes from doing the math...
Gas:
$1.409305 per therm
1 therm = 100,000 BTU
$0.00001409305 per BTU
45k BTU heater * 0.00001409305 = $0.63418725/hr

Electric:
$0.148653 per kWh
1 kWh = 3412.1416416 BTU
$0.00004356589368614093 per BTU
45k BTU = 36k BTU output
36k BTU heater * $0.00004356589368614093 = $1.568372172701073/hr

 

[zc15]

Personally I'd go 45k gas. Your needs are pry around 35k according to the calculator I used. A 45k will be enough to get up to temp quickly, especially with your near 10 foot. A 30k might not cut it for your demands.

 

[PoorUB]

I swear most of you guys are nuts! 30,000 BTU will heat a 600 square foot garage easily assuming it is reasonably insulated.

My neighbor heats a 900 sqft garage with a 30,000 BTU Modine Hotdawg heater in North Dakota.

 

[bighouse01]

I just heat my 28x40 with a standing kerosene heater when I’m out there. Which is often

 

[toyotadriver]

Again….it comes down the how well the building is insulated (southern buildings are usually much less insulated than northern buildings) so a poorly insulated building in a southern state may actually use more BTUs at 20* than a properly insulated building in a northern state. Also, a shop that is heated all the time will need less BTUs than a shop that is only heated when it’s being used and that’s most of the shops in the world.

I heat my attached 600sq ft garage with a 45k Mr Heater and my detached 1200 sq ft shop with a 80k Mr Heater. It’s overkill but has worked great for the past 6 years and I’m sure it’ll keep working well for many years to come.

 

[PoorUB]

I heat my attached 600sq ft garage with a 45k Mr Heater and my detached 1200 sq ft shop with a 80k Mr Heater. It’s overkill but has worked great for the past 6 years and I’m sure it’ll keep working well for many years to come.

Your 45K heater would heat the 1,200 sqft just fine.

As for the insulation, sure but how often do you see -30F? Is the southern states you insulate and heat for maybe 0F as your extreme temp.

You can get buy with less insulation because the difference between the outside temp and the indoor temp is much less.

I worked in HVAC for years and sized heating equipment all the time and never had a complaint. I put a 77,000BTU furnace in a 3,500 sqft house and zero complaints.

Larger equipment will heat al area just fine, but it is hard on the equipment. Properly sized you might get over twenty years on a unit heater. Sized too large and the heat exchangers rot from the inside out in mush less time. I have seen oversized shop heaters rot a heat exchanger in five years because they were over sized. The argument that a larger heater is not much more money doesn't work as you will have to replace the equipment sooner.

I really have a problem why people don't get it!

Just because it works doesn't mean it is the correct way to do it.

I need to go now and finish up the PVC airline install in my shop.

 

[yeldogt]

I swear most of you guys are nuts! 30,000 BTU will heat a 600 square foot garage easily assuming it is reasonably insulated.

My neighbor heats a 900 sqft garage with a 30,000 BTU Modine Hotdawg heater in North Dakota.

Keep telling people they oversize by many factors --- remember most utility gas are 80%

I can heat 1600sf in PA on the coldest day of the year with 15k BTU of electric. I have a cabinet heater in the space that does about net of 30 w/ propane . Gives me some headroom w/o being too big.

The best bang for the buck when building new is to spend a tad more on making a tight building -- get better insulated doors. Make things tight. Leaks kill even insulated spaces. Get a set of green hinges on the garage door if it leaks in the wind ....

 

[PoorUB]

Keep telling people they oversize by many factors

I swear even most heating contractors are clueless. I see huge furnaces installed in smaller homes all the time.

I have a 900+ sqft house, built in 1952, poorly insulated, plus I heat the basement, but I am unsure how many BTU that adds, it isn't much. I have a Ruud 60,000 BTU modulating furnace that I have it set to stage instead of modulate. On low fire it is 24,000 BTU at 95%, so about 22,800 BTU output. It will heat my house just fine until the outdoor temp hits -30F then I need the higher stages to satisfy the demand. I pull the thermostat wire of second stage and reconnect when needed. In 15 years I had to do it one time when we hit -35F a couple days. Even then it would run constantly and the temp was one or two degrees below set point. When I bought the house it had a oil furnace with a one gallon nozzle so around 100,000 BTU output, versus the 22,800 BTU I run it on now so over four times to large.

Doing the math with the square feet upstairs and the basement I am heating close to 1,900 sqft on 22,800 BTU or about 12 BTU per square foot.

 

[toyotadriver]

Your 45K heater would heat the 1,200 sqft just fine.

As for the insulation, sure but how often do you see -30F? Is the southern states you insulate and heat for maybe 0F as your extreme temp.

My 1200 sq ft shop first had the 45k. I don’t heat it full time so I want to turn it on, wait a bit, and go to work. The 45k could do it but the warm up time was just too long. Remember, you need more BTUs to warm up a cold shop….and it’s not just the shop that’s cold but everything inside is cold. So, I removed the 45k and installed the 80k. MUCH happier with it and it’s been there 7-8 years (can’t remember exactly what year I installed it). No rust. No damage. No failures. The 45k did NOT heat my shop just fine. Now if I heated the shop full time, yes the 45k would have been fine. But I, like many/most people only heat it when I use it and that takes more BTUs.

As far as insulation, most shops in zone 4 and below are poorly or not even insulated….unless you want to count bubble foil as real insulation. I live in zone 4 and my shop is probably the best insulated homeowner shop around my area. So, the typical person in my area, heating their shop only when working in there, in an already poorly insulated building, NEEDS extra BTUs. Add large garage doors (even the best garage doors **** R value wise compared to a wall and in more southern states it’s common not to install insulated garage doors) so having a heater with more BTU capability than a comparable size house becomes even more important.

Sizing a heater correctly for a house that will be heated full time is far more important to get the size right than trying to size a garage heater. While it’s never good to grossly oversize a heater, when it comes to a not full time heated and possibly poorly insulated shop building, is always better to size it on the large size instead of under sizing it.

The very best solution would be to install two smaller heaters. Use one for most temps and both when it’s really cold. But, most of us don’t have unlimited financial resources so we have to compromise.

 

[jethead102]

Finally installed the 7500w electric two weeks ago, absolutely loving it. Keeps temp easily, warms up at about 10 degrees per hour when needed. Found an inverter for $20 on Amazon so I can use a traditional thermostat with it, which also works great.

Also installed a ceiling fan to keep warm air off the ceiling in the winter due to the low fan velocity from the heater, and provide airflow in the summer. I appreciate all the insight from all y'all! Now to decide on insulation....

 

[rpahule]

I live in northern MN and I was in the same situation you are in.

I built a 26' x 36' garage and was wondering how to heat it. I didn't plan on heating it when it was built but then circumstances came along that required I heat it. I then wondered how to heat the space; gas, electric or another source. I was going back and forth between gas and electric as most people in these forums push for gas heaters over electric mostly I think because of cost. I wanted gas however after just building the garage it just wasn't in my budget to now have gas brought into the building and all the added expense at that time, that goes along with it.

I had planned ahead a little and had 100 Amp service to the garage and therefore figured I would in the sort term and install an electric heater. I just had to figure out what size and I thought like you are doing now with trying to figured out what was needed.

Here is my setup...
26' x 36' garage with a 9' ceiling insulated attic and walls. Walls are 2x6 with R19 and the ceiling is R30.
(2) 5000 watt heaters, one in the NW corner and one in the SW corner blowing into the center of the garage.
* I ran 8 AWG wire in the case I would have needed to install the 7500 watt heaters
(2) I also had wired ahead of time for 4 ceiling fans which I use two of them on low in the winter to blow down into the concrete.
(2) 30 Amp breakers in the panel
(2) Runs of 8/2 with ground, yes I went one size up just for safety.
* I would now run 8/3 with ground as I now want to remote control it with a smart thermostat and need a neutral wire for that.
(2) 5 strand thermostat wire in case I had wanted to control it from a central location which I may do now as well, but with my setup I will need a battery operated thermostat because I don't have a neutral to pull off of at the heater. You could also do an inline thermostat as well but you would need two of them, I might have done that knowing what I know now as they make smart inline thermostats.

I love what I have and I would do it again. I don't worry when the overhead doors are opened, as much as I used to, but I do open and close them as quickly as possible of course, but it does not cool down as fast I would have thought it did, even when bringing items in and out of the garage with the 18' over head door open. It costs about $100.00 to heat it and keep it at 55 and in January/February it does jump to about $130.00 but that I can factor in. I only heat it from about October to May and as you may expect it drops down in those two months as the temps are warmer, we see about $25.00 in those months. With other advances now in solar power and other electrical energy options I could always add something to offset the cost in that way and it would also benefit other electrical needy devices not just heating.