Originally Posted by taskswap
This is a common project for wood boiler folks (which, in case it wasn't obvious from other posts, I am one). It's not terribly difficult. Usually you use something along the size of a standard oil cooler - whatever fits in the dryer - and you mount it in the internal air duct the dryer has to pass air over its own heating element.
Couple challenges: when doing this you sometimes need to expand the duct in back with some sheet metal, because it's not very big. Electrical elements are very small compared to water-to-air exchangers. Not a biggie in a house, but in a bus you might need to be clever about space usage.
Also, this works best with older units, the ones still controlled by relays. They're pretty dumb and have no idea you've cut the heating element circuit. Some new units are computer-controlled like cars and shut down when this happens. Mostly the high-end LG's and such - probably not what you'd be converting, just pointing it out.
Finally, be prepared for the cycle to take a lot longer. Electrical elements can transfer heat quickly. Water-to-air units can transfer a lot of heat, but it takes more time to do it in small units. Unless you want to install a giant radiator in there...
Note: it still takes several amps to run the drum motor. Wet clothes are heavy and hard to move.
After researching dryers for some time I was surprised. In house you choose gas or electric depends what power you have. Also you can get electric ventless unit.
It is clear how gas and electric units work. Ventless are not so clear for many people. Ventless units use cold water to condense moisture extracted by hot air from clothes, hence you don't need to blow it outside.
I prefer gas dryer in house because it is much more powerful, cheaper to operate. It is a super efficient because all heat including exhaust goes though clothes.
Now let's see what is used in RV and what is practical to use in RV application.
1.Most RV dryers are ventless. Ventless unit is horrible by it's nature. It wastes tons of fresh water in dry cycle. You simply dump warmed up clean water in rv park sewer system which in most cases a septic tank/field. Also this units are electric and require a lot of amps to heat up air.
2.The rest of dryers used in RV are just vented electric units.
You can also buy a compact electric vented unit and use it in RV.
The strange thing is I couldn't find compact (24"x24") gas dryer. This would be ideal for RV application.
I also noticed most if not all dryers that come gas or electric use bottom space for gas furnace and rear for electric heating element. I started to think to combine gas and electric in one unit. When shore power is available use it when not use propane. This can be done. The problem is I can't find 24"x24" gas dryer...... GGGRRRRR.
But yesterday I got another idea why not to get 24"x24" electric dryer (tons of them cheap and even cheaper used ones), add water/air radiator and this is all....
Here are benefits:
1. available size (24"x24") unit on market
2. cheap to buy new and even cheaper used ones. Can be mech or digitally controlled.
3. can be used as electric when shore power is available
4. easy to add water/air radiator. There is a ton of space on the bottom under the drum
5. free very hot water. Diesel engine run almost at boiling temperatures giving a lot of very hot water.
Now here is why gas unit is more powerful:
Typical house unit has 3 KW heating element. 1 KW =3412 BTU, 3 KW =10000 BTU.
My typical house gas dryer is 20000 BTU which is 2 tmes more.
Even a small water/air radiator can easily give 20000 BTU.