The garage got hot in the summer, too, but I solved that problem with solar-powered ventilation fans, plus a cheap air conditioner for the really hot days.
I installed insulation in the walls and roof, then paneled everything in plywood. I hired an electrician to install an upgraded circuit-breaker box and lots of power outlets, and I planned to get a natural-gas line run out from the house and a proper gas furnace installed, or maybe just bite the bullet of costly electrical bills and use a 220-volt electric heater made for garages. But then I remembered that my local self-service wrecking yard was full of discarded recreational vehicles, and plenty of those RVs had nice forced-air propane furnaces. I love junkyards! Junkyards are great! And so I committed to a means of garage heating that mostly didn't work and required years of constant tinkering and return trips to buy more junkyard RV furnaces.
I spent my college years living in an on-campus RV park in Southern California. It was a great place to be a car guy, and I did major automotive projects there. Living in a 1969 Roadrunner camping trailer with propane furnace, stove, and water heater taught me a lot about dealing with RV propane appliances, and I figured this knowledge would make installing a propane-fueled RV furnace in my garage an easy process.
Every one of these RVs is a wonderland of biohazards, sharp edges, and general ickiness. They smell better in winter, so there's that.
I headed over to the RV section of a nearby self-service yard and found a gigantic Winnegabo with a Suburban NT-30 forced-air furnace, rated at a mighty 30,000 BTU. My garage is bigger than an RV's interior, but it has much better insulation and I don't need to be kept at the toasty 85° favored by octogenarian road-trippers.
The furnace cost me a mere 50 bucks, plus $25 more for the 12-volt/45-amp DC power supply from the same RV, but it was a dirty, foul-smelling couple of hours to remove it. RVs that get bad enough to get scrapped are always horrible inside, generally full of hantavirus-saturated rodent poop, dirty syringes, and septic-tank leakage on everything. I wore gloves, goggles, coveralls, and steel-toed boots while yanking this furnace and my skin still crawls at the memory of the stench in there. Tip: junkyard RVs don't smell as bad inside when it's below freezing.
Bench-testing revealed that the furnace made heat, but with a terrible bearing scream from the blower fan.
In what I should have interpreted as a warning, bench-testing the furnace and power supply revealed that the blower fan's bearings were bad. No problem, I'll go back to the junkyard and get another $50 furnace! Which I did.
Naturally, the gasket on the blower-fan housing fell apart, so I had to make a new one out of cardboard.
I dismantled Furnace #2 (which came from an even more unsanitary donor RV) and removed the blower fan, which (miraculously) turned out to be good. Then I had to cut a new gasket for the fan housing.
These Suburban furnaces are pretty well-made units, but owners of RVs— particularly final owners of RVs— mostly don't do any maintenance on their furnaces, and even the best-cared-for RV tends to spend months and often years sitting unused. Because these furnaces have exhaust and intake ducting to the outside world, wasps like to build nests inside the blower fans and combustion chambers, and then there's the problem of hungry rodents chewing on wires. Accessing some of the stuff that needs fixing is a finicky, painful process involving a lot of cuts from sharp sheet-metal edges.
Fresh air for the furnace's combustion chamber comes in through the bottom hole, exhaust goes out the pipe.
I used correctly bent and sized flared copper tubing with the right fittings to supply gas from the propane tank, which lives outside, on the other side of the wall from the furnace. Exhaust is carried away via a pipe long enough to clear the roof eave. I'm using an LP gas pressure regulator with overpressure valve (also mounted outside), and the furnace itself has thermal-overload and flame-detection sensors.
Then I added four carbon-monoxide detectors inside the garage, because dying sucks. One would have been enough, but I didn't want to take chances. Other than the occasional alarm when I pull a non-catalytic-converter-equipped vehicle into the garage, my CO detectors have remained silent during the three winters I have used an RV furnace for garage heat. It's safe, but not reliable, as we'll see.
After much futzing, it worked! With 30,000 BTUs and ducting to the distant corners, my furnace could get the garage from 20 degrees to 60 degrees in an hour or so. However, in all the time I've had this rig, its longest trouble-free period has been about six weeks.
Propane consumption isn't high enough to be a big financial hardship, thanks to the serious insulation in my garage (including the big door), but I always run out when a big snowstorm comes in, it's ten degrees out, and I have an important project to do. They must hate me at the hardware store where I get my tanks filled.
Some of the older furnaces of this type use an old-fashioned pilot light for ignition, but post-middle-1980s units have electronic ignition with flame detection. The control board goes bad, especially in ill-maintained RVs with bad power, and then you don't get heat-- the blower fan just spins and nothing happens. After misdiagnosing the problem for months, I finally found a company making aftermarket ignitor boards and bought one. More money into this allegedly cheapskate project!
Then the 45-amp power supply went bad, frying my new ignitor board and requiring replacement with an expensive modern switching unit. Then the LP gas regulator went bad, with symptoms identical to those of a dead ignitor board. Keeping my garage warm was taking as much work as keeping the electrical system in a Jaguar XJ-S operating perfectly, and with a similar success rate.
The low point came a year ago, when the furnace failed on the day before my big Junkyard Boombox Building Party. With temperatures in the 20s, I had no choice but to run to the junkyard and get another RV furnace, this one a 14,000-BTU unit with an old-fashioned pilot-light ignition system.
The temporary replacement furnace had a forced-air blower, but it made just barely enough heat to get the garage up to 45 degrees and it took several hours to reach that not-so-comfortable point.
24v Dc Exhaust Fan
I have spent close to 500 bucks on this setup so far and I still can't count on it when I need warmth. For next winter, I'm going to do what I should have done all along: hire professionals to install a proper natural-gas furnace in my garage. Yes, it means more money and probably tearing up my flagstone yard to run a gas line from the house to the garage 50 feet away, but in the long run it will be cheaper that way.
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