Heat source for garage floor hydronic heat
Newbie trying to figure out best approach for radiant heat for a 3rd bay garage/workshop. Question is, what heat source, electric boiler or geothermal heat pump with a ground loop or should I go for something completely different
I am right at the Zone 5/Zone 4 border in Grand Rapids MI area, property is riverfront. Summer humidity gets pretty high.
Space is 14×26 with 10 Andersen 2×2 400 series awning style windows up high. Walls are 2×4 frame with sprayed closed cell foam insulation. 10 foot ceiling. 3 walls are exposed to environment. The 4th (interior) wall is the original 2 bay unheated garage wall. This wall is also foamed. Attic/ceiling is not yet insulated. The house is on the other side of the original 2 bay garage. I have a 9ft wide x8 ft high overhead door that clearly is not as airtight as it might be. Door is insulated.
The floor is not yet poured and I want to do a radiant heat setup. I am pretty sure I want radiant heat as I am generally comfy if my feet are. I plan to keep the space at around 67 in the winter and ambient temps in the summer.
I called a local HVAC outfit out and asked or a quote for geothermal and received a quote for mini-split setup.
I do not have natural gas available, house is all electric. Access to power is no problem, the meter and main breaker panel are in the 3rd bay.I can get water to the 3rd bay although it is a little awkward. I’ll have to trench and repurpose the original well supply line to the home. Recently got city water and well was plugged. I would just have to salvage the well end of the water line and redirect to the 3rd bay.
I would appreciate any thoughts or suggestions on reasonable approaches to make this space comfortable to work in during winter months.
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Replies
This is such a small space geothermal will be at a major cost disadvantage so I think electric boiler is your best bet. Your monthly bill will be higher but your total costs will be lower. Geothermal can't compete that well.
It might still make sense to install a ductless air-to-air heat pump - the cost is low enough that it might be worth it if the radiant isn't as comfortable as expected. You can do this after a winter.
I would vote for none of the above.
The quote that came back with the mini split is right on. If you are doing dusty work, get one of the slim ducted unit installed with just an intake filter with not a regular wall mount is fine. This can left exposed and be hung from the ceiling the same as a shop heater. I would get an oversized unit which would let you set back the temps when not in use and crank it when you need it.
For standing comfort, your best bet is a layer of rigid over the concrete with plywood tapconned down. This gives you a low mass surface that is quick to heat up when you are in there. Much lower thermal conductivity so it won't feel cold plus the extra bit of compliance makes it easier on the joints.
Anything hydronic simply won't pencil out. About the only thing that would be somewhat cost effective is the resistance boiler but at that point might as well install an oversized resistance shop heater as it is exactly the same energy use and a fraction of the cost.
Hydronic heat + AC will more than double the equipment and install costs.
If propane is off the table. Understand the operating cost for the electric boiler will be 4 times that of the air to air heat pump.
Air to water heat pumps are almost as rare as hen’s teeth and very pricy. My opinion not ready for prime time.
If the heated floor is a must have consider feeding it with an outdoor wood fired boiler and have A to A HP for AC and when you are unmotivated to fire the wood burner.
Walta
If you are just looking for a heated floor and no cooling, you might get away with one of the ~$2000 pool heat pump water heaters. Just a circulation pump, the heat pump and the lines. You might lose capacity in the absolute coldest week or two of the winter. This would be a bit experimental.
Thanks for all comments, definitely things to consider. Not planning on AC as shop stays reasonably comfortable in the summer as long as doors stay closed.
Since the workshop may at some point have a vehicle in it, I am not inclined to put down rigid foam and plywood.
Cost is one consideration but comfort is more important to me. I would rather pay more once and be comfy than save money now and be uncomfortable for the next 20 years. As I get older, I seem to get cold more easily and it has more effect on my productivity.
Thanks again for the valuable input and options.
I'm also in Michigan, put a $700 eBay mini split in 4 years ago and it has made my shop significantly more comfortable. But I have an uninsulated slab and even when the air is warm, standing at a machine or going under a car is still a bit uncomfortable. An insulated slab would probably help with that a lot.
Car tires are somewhere around 30psi ground load which is not a lot. If you go for higher density (say 60psi type 3 foam) with a thicker T&G, you can drive on it without issues. It would not work as car storage but it can certainly work for occasional use when you need to work on your car.
Lot of this depends on what the space will be used for. If mostly workshop, I would go for a wood floors. If it is mostly car shop, concrete is really the best.
For a garage to studio conversion, I went with the similar route as Tim_O. With a well sealed and reasonably insulated space, the heating costs are so low that I don't even bother turning the heat down. I would however not go with a bargain basement unit again as it doesn't do all that well in snowy climate.
If you are going with a heated slab and zero under slab insulation seems like a mistake as the 50° earth under the slab will suck up a lot of BTUs.
If you know where the lift will go you could have it engineer for insulation and the lift with a thicken slab in those areas for not much money.
I don’t see heated floors in a wood shop as much of an upgrade as I never work in my shop bare foot. Maybe better in an auto shop when the overhead door gets opened often.
How many hours were you in your shop last week? Lots of us imagine spending 40 hours a week in our shops but I might get 4 on average. It would make me craze if I was spend the money keeping it warm and did not get out there.
If there it seems like you might end up using your shop like I do consider get some big electric heaters that can get it from 35° to 75° in 20 minutes or so.
If you get this wrong you will spend lots of money every month paying for fuel.
Walta
I spend about $50/month on my heat pump. I used to spend 10-15 hours a week out there. Now, I get maybe 3-4 hours a week. But I like to be able to walk out when I have 20 free minutes, make a part, complete a task on a bigger project, whatever... And not have to plan for that short time out there.
The other nice thing is keeping temperatures up and a bit more stable helps a lot with keeping your tools rust free.
AS one of the few here who has actually had a radiant heated garage I can offer this:
Stop
First insulate the floor well. 2 inches around and under and across the door aperture
Second seal the door well. There are ways to get it done, maybe I will make a detailed post someday
If you want to be comfortable,. install a minisplit and you will have air and heat
With the floor well insulated and the heat running regularly, you will be no more uncomfortable than you are in the house.
Yes my radiant heated garage was awesome, but all I had to do is run a hundred bucks of tube and hook into my existing boiler.
An insulated and airtight heated garage is not comparable to a drafty old barn, you will be plenty comfortable with a garage kept at 50 degrees and warmed up via your phone on your way home from work
I like to say an ounce of insulation is worth a pound of hydronics. You get a lot more comfort for your money making a building tight and well-insulated than you get trying to make up for the lack of insulation with a better heating system.