What size heater/heatpump?

[VietGnome]

I'm deep in the planning process of my garage build this summer.

I was originally planning 4x 240V 50A circuits. Heatpump, lift, welder/compressor, and EV. I don't own any of those currently, but I'd like to factor it into the build since it's easier now than later.

I was originally planning on running every circuit at 50A. But apparently running 6AWG all over your 1200sqft garage adds up... Trying to cut down circuits to 30/40A as required, one of those is the heatpump circuit(s).

I don't plan to finish the garage this summer, and hopefully over the winter/next year I can insulate and heat it. I'm currently planning to blow R40 into the ceilings, and R21 into the walls. I live in Eastern Canada, so winter is real. I'm considering heatpumps but don't know what size. I've scoured some older posts but results vary, and lots of replies are from more temperate climates. I don't foresee me using AC much, but the dehumidifying in the summer will probably come in handy.

I don't want to keep it blazing all winter. I would keep it around 10C and bump it to 15 when I'm working, but I understand heatpumps tend to not go below the 15C range, so that's what I'll settle for. Not sure on sizing, if I should go for a single bigger unit (30k?), or two smaller 15-18ks?

Thanks for any advice.

 

[jlv03]

Do you have natural gas available? If not, and if only going electric, you may be better off with two smaller minisplits rather than one large one (and the large wire that goes with supporting it).

 

[ericm]

I don't want to keep it blazing all winter. I would keep it around 10C and bump it to 15 when I'm working, but I understand heatpumps tend to not go below the 15C range, so that's what I'll settle for. Not sure on sizing, if I should go for a single bigger unit (30k?), or two smaller 15-18ks?

Rather than guessing you could do a load calc (Manual J in the US) and sizing (Manual S) for your building. Or have it done. Then you'll know. I used l leoadcalc.net to get the sizes of the mini splits for my shop. It's a bit tricky in that it won't tell you when you have left a field blank that you should have filled out. But after messing with it a bit I managed to get numbers pretty close to the load calc the HVAC contractor did for my house It had a much more complex shape than the shop and that is likely where I made errors. I've been really happy with the units in the shop so far. Winter is the test here as heating needs are greater than cooling.

Some mini splits can be set for "freeze protection" at something like 45 degrees F. I leave mine at 60, which is a fine temperature for me to work at.

Mini splits usually do not have a lot of excess capacity like most gas heaters (which are often oversized). But with that said if I leave a 12x12 door open while moving stuff in and out, or even two like today, the units crank up and bring it up to temp pretty quick. But all the stuff in the shop, slab, etc is already at that temp, so they're only heating the air back up. It will take longer to bring the slab and the objects in the room up to temp.

My 2240sq ft heated shop's power usage this winter has been in the 10-20 kwh/day range to run the mini splits. Our power costs about $0.16/kw. I'm ok spending a few dollars a day to keep the shop heated so it's comfortable as soon as I walk in.

 

[danski0224]

Rather than guessing you could do a load calc (Manual J in the US) and sizing (Manual S) for your building. Or have it done.

OMF'NG

 

[VietGnome]

Rather than guessing you could do a load calc (Manual J in the US) and sizing (Manual S) for your building. Or have it done. Then you'll know. I used l leoadcalc.net to get the sizes of the mini splits for my shop. It's a bit tricky in that it won't tell you when you have left a field blank that you should have filled out. But after messing with it a bit I managed to get numbers pretty close to the load calc the HVAC contractor did for my house It had a much more complex shape than the shop and that is likely where I made errors. I've been really happy with the units in the shop so far. Winter is the test here as heating needs are greater than cooling.

Some mini splits can be set for "freeze protection" at something like 45 degrees F. I leave mine at 60, which is a fine temperature for me to work at.

Mini splits usually do not have a lot of excess capacity like most gas heaters (which are often oversized). But with that said if I leave a 12x12 door open while moving stuff in and out, or even two like today, the units crank up and bring it up to temp pretty quick. But all the stuff in the shop, slab, etc is already at that temp, so they're only heating the air back up. It will take longer to bring the slab and the objects in the room up to temp.

My 2240sq ft heated shop's power usage this winter has been in the 10-20 kwh/day range to run the mini splits. Our power costs about $0.16/kw. I'm ok spending a few dollars a day to keep the shop heated so it's comfortable as soon as I walk in.

Thanks, makes sense. New to it all. I tried that site and it fried my brain a bit and I'm not sure what/how to fill out a lot of the blocks, yet other load calcs I find are on the opposite end of the spectrum and so broad.

It SEEMS from my research I should be good with a single 24-28k, but ill keep messing with that site and see what I can cook up

 

[ericm]

You can post your loadcalc and I or other people here can look for missing fields. Also you're supposed to use the Manual J data to run a Manual S to size the equipment. S bumps up the size over the number from J.

I put in two 24k units for 2240 sq ft with 14f ceilings, R21 in the walls and R60 in the ceiling. Design low temp was 24F. That's supposed to be the 99th percentile low. The ceiling R value won't make a huge difference but if your design temp is way lower you may be undersizing.

Smaller units are more efficient per BTU than larger ones. Two units help spread heat around. And if one dies you have one left. But they cost more than a single unit for the same BTUs.