How much heat can you get?
Oil Cooler v Heat Muff heater
Oil Cooler Cabin heater - There are not many or any factory planes using oil coolers for heat. Why? I don't think it's because they did not think of it in the last 70 years. It might be a clue about design choices, trade-offs and return for effort. As far as LongEz's their cabin is much smaller in volume and much better insulated than a RV. Still I don't think oil-cooler cabin heat is common in LongEz's (could be wrong).
How hot can you get the air for the oil-cooler? It depends on oil temp/flow into the cooler. It also depends on air temp/pressure/density across the oil-cooler. Doug does not want "rocket scientist" heat transfer equations on the forums, but lets say on a 90F day, your oil-cooler raised air temp going through it 80-90F. However on a freezing day that total temp rise goes down, let's say in half (or more). The air of course is colder and more dense to start with. The engine is also running cooler so oil temp is less. The oil cooler might only raise air temp 40F on a 10F day. You will be cold. Besides temp, there air flow (pressure/volume).
Oil coolers have little fins & tubes for air to pass through, significantly dropping air pressure (more than a heat muff). The air pressure coming out of the cooler may be pretty weak. If the cabin is air tight, your hot air can't get in. A good cabin air exit vent improves air flow. If cabin air pressure is higher due to leaks, than the oil cooler's low pressure flow will be nill; you're going to be cold.
HEAT MUFFS, suffers as well when the engine is running cooler due to low outside air temp or lower power settings, just as the cooler does. Hot exhaust air starts out at say 1,800F (3,000F-4,000F in the combustion chamber). You can do to get more heat out of heat muffs. Heat studs (welded on), making your pipe look like a porcupine, adds more surface area. The heat muff goes over the studs. Check with, either
AWI or
AEI for the stud welding service. (
Pic) Also keep the SCAT short; Route the air into the heat muff downstream (@cool end). The exit air from the muff to the cabin is at the higher temp end.
How about DUAL heat muffs? Larger, longer heat muffs? Increase SCAT from 2" to 2.5" to reduce pressure drop? (There are no off the shelf 2.5" parts, so that's a negative, requiring custom parts and FW air valve.) Heat muffs get a bad name because the ones Van's sells are too small for cold climates. Coastal Oregon is wet not that cold. I think 50% of the problem is leaky cabins and 50% undersized heat muffs. I know how tight it is under the cowl, so fitting bigger any thing is a challenge.
Is the oil-cooler cabin heat worth all the effort? Good luck if you try it and let us know how it works. There is always just dressing warm (I'm not kidding). Not having little cold drafts squirting cold air on you neck is a plus. You have to think of the RV as a motorcycle, are real fast one with a really good fairing. Regardless of what you do, most RV's are uninsulated, will always leak and do not have a good exit air vent.
Wild Idea? (heated clothing & liners for snowmobiles & motorcycles)
Link,
Link,
Link The amps are kind of scary in the 3 to 7 amp range for each item. Don't laugh but another trick is a blanket. If you can get some of your hot air vent air under the blanket, its very comfy. Just attached it under the panel and over the stick and chest. Kept, legs, hands and chest warm. It saved my life on a winter coast-to-coast flight.