Most energy/cost efficient way to heat insulated garage workshop
Hello GBA members!
We live in Vermont (zone 6A) and have a 16′ x 24′ single bay converted garage woodworking shop space that’s part of a converted apartment. Originally it was a 2 car, 36′ x 24′ garage, but we converted 20′ x 16′ of the first floor as well as the entire “attic” space into a 2-bedroom ~950 sq ft, 2 floor apartment. The remaining garage bay is insulated but currently unheated. We padded out the walls of the apartment with furring strips to 6″, but left the garage with 4″ walls that are insulated with R-15 rockwool insulation. We are using spray foam and 2″ foam board to insulate the garage door and are planning to put in a plywood floor above the garage floor so that we can insulate above the existing slab floor.
We need to figure out still how best to heat the 16’x20′ converted garage woodworking shop, which has 8’6″ ceiling. We don’t use the workshop enough that it seems to me to make sense to keep it heated 24/7, though we probably use it 3 or 4 days, sometimes more, a week for at least a couple hours, sometimes longer. Perhaps I’m wrong and keeping it heated to 50 when not in use would actually be more efficient, if using something like a small mini-split heat pump. I really only need it to be 60 or 62 when in use, not 70, since I’m usually layered in the winter. Most of the time the outside air temp during Nov-April, when we need heating, is upper 20s, lower 30s, and in Jan/Feb, maybe into the teens and sometimes, but not often, single digits.
The apartment is heated with a fairly efficient combination propane boiler paired with a radiant floor system. One possibility for heating is to add a zone for the garage. We could also add in a propane heater, as there’s already a T in the supply line to the boiler that we could easily connect to.
An ideal system would be the most affordable considering both equipment/installation cost as well as lifetime fuel costs, something that wouldn’t take a long time (10 to 15 minutes max?) to heat up the space if we’re only using it for an hour or two and leaving the heat off the rest of the time, and, if possible, is being run on electric instead of propane, since I’d like to convert the whole property to high efficiency electric heating at some point.
Suggestions? Thanks in advance for your time and expertise!
-Eric
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Also, would radiant heating panels or radiant tube heaters be effective/efficient in this situation? I've seen some reviews suggesting them, though it seems like most are sponsored by the retailers or manufacturers and I can't find much of anything positive from independent sources. Something like this guy has in this video: https://www.youtube.com/watch?v=TYzLy2gRfpo
For at least four decades marketers have been pushing the idea that infrared heat is more efficient, because you feel warmer with less actual heating happening. I remember seeing that idea pushed in the 1970's. The fact that it hasn't gone mainstream should tell us something. If you've already got a boiler you can get nice "hot" heat, I think that would work better for you.
Thanks, that was what I figured the situation was, nice to have confirmation.
Sounds like what you want is something that is oversized for the space so it can quickly bring it up to temperature when you want to use the space. I'm thinking adding a zone to the boiler with a large convector is probably simplest. Second would be adding a propane space heater. Heat pumps aren't good for large immediate blasts of heat. If you add a zone you have to either have anti-freeze in your fluid -- which is recommended anyway -- or make sure it never freezes in there.
Hi Eric,
It’s really stretching the truth for a manufacturer to call any boiler efficient (is the Hummer H2 efficient? Only if compared to the H1). A minisplit can handle this task really efficiently and cheaply. The EIA has propane at $2.7/gallon, which with a 99% “efficient” boiler is ~$30/MMBtu. I haven’t a clue what your electricity costs, but if it’s around the average of $.13/kwh, a cold climate heat pump should get you a MMBtu for ~$9.5 (they get more efficient as indoor setpoint approaches outdoor temp, so high COPs are expected). If the recovery takes too long, just set it higher or get creative with the thermostat programming.
"Efficiency" is one of those words that has so many meanings it's almost meaningless by itself.
It can mean "cost-effective." In this case, he's already got a propane boiler, almost certainly the lowest initial cost is going to be just adding a zone to it.
I'm not sure in this application that a minisplit is going to do that well, where he wants to be able to heat the space up quickly after leaving it unheated. Some will switch to resistance heat if the room temperature is more than a few degrees below the set point. If that happens you lose any COP advantage and the cost per Btu is going to be very close to propane.
Yup, cost effectiveness is definitely a concern. If a Mitsubishi minisplit can be had for $3-4k/ton, how much are you realistically saving by adding a zone? Antifreeze, a panel radiator (or two or three), piping, valves, possibly a circulator puts you probably around a grand before any labor or markup. If you ever use the room more, you run into the high cost of propane and he wants to get away from that. Plus AC is added in for free.
A minisplit usually won’t have a resistance backup. The cheapest upfront option is likely resistance baseboard - but then the operating cost probably exceeds propane.
I just paid $17k for three Mitsubishi Hyper Heat mini split condensers and 6 air handlers. "Cheap" they are not. Inexpensive to operate, yes.
We're talking about a <400 sqft open space here. He won't need 3 outdoor and 6 indoor units...
Look at this mini split, a 1 ton unit that heats down to -13F. I think it would meet the needs of a 400 sf space. $1050. The technology that was once reserved for Mitz and Fuj has rapidly moved to the Chinese manufacturers and the prices have come down. It seems to be similar to what happened in the 70's with Japanese import cars being cheaper and very high quality. You no longer have to look down on Chinese manufacturing quality being inferior.
https://www.homedepot.com/p/Pioneer-Inverter-Energy-Star-12-000-BTU-1-Ton-Ductless-Mini-Split-21-5-SEER-Wall-Mounted-Air-Conditioner-w-Heat-Pump-WYS012GMFI22RL-16/311771300
Here's another option:
https://www.homedepot.com/p/Pioneer-Inverter-ENERGY-STAR-24-000-BTU-2-Ton-Ductless-Mini-Split-20-5-SEER-Wall-Mounted-Air-Conditioner-with-Heat-Pump-230V-WYS024GMFI22RL-16/311882201
It's the same version with 2-ton capability. $1688. If you want things to heat up faster this unit would be the ticket. I don't think $600 more would break anybody's piggy bank. Especially compared to the $17,000 bill that was suggested.
You have to be careful with the Pioneer units. They make a decent AC, but are pretty lousy heat pumps. The capacity on most units tanks when it gets cold. For example, the unit linked looses 50% of its rated capacity at 17F.
For a couple of extra dollars, you can get a Gree or Midea hyper heat unit.
Some of the models maintain their nameplate capacity down to -5F. Even if you don't need the low temperature performance, they tend to be a better option as they deliver heat well above their nameplate capacity in a milder climate.
My understanding was that the Pioneer brand is a rebranded Midea. Is that incorrect?
EDIT: Akos, I hadn't seen some earlier threads here that said pretty much what you said. My case is less critical as I live in California. But it would be important if living in Vermont.
Here are two Gree units that work down to -22F. They are slightly higher in price but their equivalent BTUs for heating and cooling for rated BTU are better than the Pioneers. The 1.5 ton model:
https://www.homedepot.com/p/GREE-Sapphire-18000-BTU-1-5-Ton-Ductless-Mini-Split-Air-Conditioner-with-Inverter-Heat-Remote-208-Volt-to-230-Volt-60Hz-SAP18HP230V1AW/303540387
Around $2250
The 2 ton model:
https://www.homedepot.com/p/GREE-Sapphire-22-000-BTU-2-Ton-Ductless-Mini-Split-Air-Conditioner-with-Inverter-Heat-Remote-208-Volt-230-Volt-60Hz-SAP24HP230V1AW/303540385
That one's $2150 right now. Those two units might be better for Vermont conditions.
Major manufacturers make a couple of tiers of equipment. Lot of times the ones made for other brands tend to be bottom tier units.
You can search around a bit a find something better, for example the Mr Cool's Universal is a Midea hyper heat unit with fancy fittings. Often it is better to go with a Gree or Midea instead.
Even in milder climate where you need more heat than cooling a hyper heat tends to be a better fit as they tend to be not so oversized for cooling load.
I concur with Paul. It's improper to connect propane and efficiency together. It is also not at all green. If you are connected to the grid propane is just not the way to go except for backup. Take it from someone who used to have propane and has become a convert to heat pumps. Their lifetime costs are much lower. It is not smart to rely on short term thinking. This applies both to making a cheap and fast installation and also to desiring instant warm up of rooms.
Even the lowest cost Midea rebranded heat pumps can be made to work and to work well in your situation. I think they all have a "do not freeze" setting that keeps things around 46F. This is still an efficient mode to use provided your space is reasonably insulated, which your space seems to be.
Around me, propane heat is pretty close to the cost of resistance heat especially if you already have a base load that is covering your connection charges. Probably the simples is a couple of oversized resistance panels.
I went through similar dilemma a while back for heating a studio, in the end ended up going for an oversized budget wall mount mini split. Best decision ever. Cheap to run, can get the place up to temperature in no time and cools the place in the summer. It is cheap enough to run that I don't even bother to set back the temperature most of the time.
In case of a wood shop, wall mount would not be the best, I would go with a slim ducted unit but treat at as a ceiling mount garage heater. Just install it to the joists without any ducting and mount the biggest intake filter box you can find space for. Make sure the filter box is well sealed, can take a large standard 4" filter (ie 20x25x4) and change the filters as needed.
I've used ducted units for heat during construction and a well installed merv 13 filter does a good job of keeping most construction dust out of the unit and ductwork.
Last winter I had a Fujitsu minisplit installed in my garage/shop in Maine for $3700. I usually set it to minimum heat, 50°F. If I won't be using the shop for days, I turn the heat off. But it's pretty slow to warm up. For example, today was windy and cold, mid 30s. Inside this morning was 42°. It took around 4-5 hours to get up to 52°. The garage is insulated, not particularly well air sealed, with 2 doors. The space is 24x34'. For my purposes, it works well.