Heating a Tuck-Under Garage
Hello,
We have a house with a tuck under garage in climate zone 7. Insulated in walls and ceiling with R-21 fiberglass and polyethylene vapor barrier facing the garage interior. Drywall taped. The garage door is insulated, R-8 at the worst and R-18 at the best, but we do not know the R factor at this time. Our intent is to make it usable space and not put cars in there. We likely will not be using the garage door. We may use the space for light woodworking. For the winter we’re looking to keep it mold free (dry and warm enough, just above 50 degrees). But we’re not sure how to heat it.
We know some mold grows between 30-50 degrees in the winter and in the summer some grows at higher temperatures (and of course with humidity in the summer). So for the winter we want to keep it warm enough (50 degrees).
We had been looking to remove or close off the garage door but have changed direction due to cost. We will leave the door as-is and try to seal it up better. I’ve installed Green Hinges and will add more insulation to door using a polystyrene kit. We are also looking at sealing around the door. It currently has an exterior weather seal.
We’re not sure how best to heat it. We’ve seen gas-powered garage heaters that hang from the ceiling — but since heat rises isn’t that going to be uneven? We’ve seen electric radiant options — but wouldn’t the electric bill just go way up? We’re just really not sure what to do. We’re looking for a balance between monthly bills and cost to install.
Thank you!
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Replies
The easiest way is probably to direct some heat from the rest of the house. How is the rest of the house heated?
What's it like in there currently in the winter? Even if you don't heat it directly some heat will seep in and warm it. Unless you have water leaking in from somewhere, in zone 7 I would expect it to be very dry in winter, the outdoor air is going to be extremely dry. The only source of moisture would be air from the rest of the house leaking in. In general you want the barrier between a garage and the rest of the house to be as airtight as you can get it.
So long as it is possible to get a car into this room the local code and fire officials would be very unlikely to approve any plan that extends the homes heating system to the garage without barricades that would keep cars out of the space.
I doubt mold will be a problem unless there is a large moisture source in the space assuming you heat the space enough to keep it warmer than the dew point of the air in your home.
Installing electric base board heaters will have the lowest up-front cost but the highest operating cost. This could be the best option is the space will get heated for a few thousands of hours. Say if you needed heat 24-7 6 month of each year and you were going to move in a year or 3 or if you would only heat the space a few hours a week and stayed for 20 years.
If the space will be heated 24-7 for the foreseeable future, then it would make sense to add a more expensive system.
Walta
I put a mini split in my active garage, but realized after a while that since I don't run it much in the summer, at all in the shoulder seasons, and on very low in the winter, I had high moisture levels
A portable dehumidifier solved my moisture issues, and it adds some heat to the room.
Garage doors are routinely badly installed. make sure it sits tight against the seals such that you do not see light when the wind blows.
That moisture is probably coming in during the summer and dehumidifier is the appropriate treatment.
The original poster's premise that lack of heating in the winter causes mold is not correct.
I have experienced cold weather mildew, not really mold. I assume it has to do with variations in temperature, objects going through the dew point. Mine is an older[30+ years] structure so no doubt suffers more moisture ingress than a newer structure.
I feel like a dehumidifer is a pretty cheap potential solution, although I might tend to wait for a problem to arise before doing it.
Use a gas fired unit heater, such as the Modine Hot Dawg that is made for exactly this application. Yes, heat does rise, but the heater has a fan in it to blow the heat around. The result is reasonably even heating, although you will have more noticeable cool/warm areas in most cases since the heater is equivalent to using only one vent from a furnace to heat a good-size space. Heat rising won't really make any noticeable difference unless you have a very high ceiling in your garage.
Don't try to tie your home's HVAC system into the garage, since that is a code violate. As long as the "garage" can still be used as one, code applies. If you were to remove the overhead door and replace it with a wall, something like that, then you could claim the garage as part of your home.
If you have a hot water heating system (boiler and radiators), then it would be possible to run a loop to the garage and use a hydronic heater hung from the ceiling. Hydronic heaters are just like that Hot Dawg unit, but they have a radiator inside instead of a gas burner. If you have an existing hydronic heating system in your home, using a hydronic heater in your garage tapped into your existing boiler would be my first choice -- assuming you have some extra capacity available on the boiler (which is usually the case).
An electric unit heater would be an electric resistance heater, and that is almost always the most expensive way to heat a space. The upside with these is that they require no venting, and only an electric circuit to operate (usually a large circuit though), so they tend to be the cheapest units to install.
As long as you keep the space warm enough to be above the dew point, you shouldn't have any issues with condensation.
Bill
Hey Bill, thanks. No intention here to tie it into the house HVAC unless or until we fully convert the garage, meaning, no more garage door. At one point, we were going to actually pull out the garage door and have a wall built in its place, but we don't have plans to do that anymore. We know it's a code violation (and just bad for many reasons) to tie the HVAC into the garage if it's still essentially a garage, despite us not really using it as one at this point.
We found mold in the garage today. We knew there was likely mold because of the way it was built. We had mold samples taken that indicated much higher levels of aspergillus than outdoors, but we hadn't found the source and another "expert" suggested it might have just come in from outside. We started examining around the garage door to caulk before freezing temps came on, and found a lot of mold on an unpainted piece of wood directly above the door. We applied concrobium but with the amount we found, we're likely to cut the piece out and nail a fresh piece in there, with concrobium applied and everything caulked very well around it. We're thinking of electric heat for this first year because we don't really know if that'll be the end of the mold. Given how it was built, with the garage open during tropical dew point conditions, we can't be sure it's not in the cavities (the builders agreed to dehumidify the living space while building, but then just left the garage open during the worst weather and dew points). Safest bet seems electric heat this first year so that if mold remains we're not getting it in the furnace.
Mold like you're describing is much more of a warm-weather phenomenon that a cold-weather one. When it's hot and humid outside it's common for enclosed spaces to stay cooler than outside, and if outside air leaks in condensation can result. Showing up directly over the door is a pretty strong clue that what you're seeing is summer air leaking in.
In winter the outdoor air is going to have a much lower moisture content than indoor, any air that leaks in will tend to dry things out. The source of moisture to worry about is the warm air inside the house, that can cause condensation if it leaks into a cold garage. That condensation would manifest on the wall between the house and garage.
You really want that wall to be as air-tight as possible anyway, for efficiency and comfort of the house, and to prevent smells from the garage from entering the house. If it was properly constructed it should be insulated and have some sort of vapor blocker on the warm side of the wall.
If you found a lot of mold only on one specific piece of wood, I'd be suspicious of why only that piece. Check if there are any missing flashing details or other things that might have caused excessive amounts of water runoff to be directed at that moldy piece, or if that moldy piece was positioned in a such a way that water could pool up on it or otherwise keep it wet longer than the rest of the structure. Fix anything you find to help prevent the problem from recurring in the future.
Bill
Before doing anything I would take some measurements of actual temperature and humidity, you can get a logging WIFI sensor on Amazon for less than $25. Here's one:
https://www.amazon.com/dp/B08YRKLHLD
If you pay money to a mold removal company, they will find mold in any building anywhere on earth. Mold is literally everywhere the only question is are you currently given the mold enough heat, moisture and food to grow now.
If you can’t smell the mold, it is not likely to be a problem unless someone is super sensitive with some hypochondriac tendencies.
Walta