Waste oil heater exhaust options?

9 LIVES

9 LIVES

Demolition Expert
So I have a free burn waste oil heater kit that I assembled last year. It worked great when I could get it to flow the exhaust well.

Is their an art to getting proper exhaust flow?

The first 5-10 minutes the heater runs practically all of the exhaust backflows into the shop until the heater gets up to around 800-1k degrees. Ive been using 6" stove pipe.
 
My 6" stove pipe comes off the top of the top barrel and goes up maybe 2' then 90* goes towards the shop wall to exit the wall which is a 4' run of 6" pipe.

Once it exits the shop wall to the outside its another 1' piece before it has another 90* bend to go upwards. 4' vertical section to a rain cap.

Someone once told me I need to go higher up then 2' off the top barrel before I go 90* towards the wall but they never mentioned how far " Up "
 
I don't understand why would the exhaust flow back into the shop? Do you not have a flue that leads out the roof? Or are you talking the exhaust does not float away from the top of the flue enough? If it's the latter the exhaust is cooling too much. The flue also needs to be properly sized.


I read your last reply, it's better if it goes straight up. You could also try insulating/double walling the flue pipe on the outside. It's cooling too much.
 
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I don't want the exhaust coming into the shop. It does it on it's own!

The heaters outside wall temp is around 1K+ and the exhaust going through the shop wall is around 150-225*. Is that cooling to much?
 
Is the exhaust reversing or is it coming in from the outside?

How is the air fed into the unit for combustion?
 
Small fan the size of my fist blows air down a 2" steel pipe into the burner unit. Down the center of that 2" air pipe is a small copper pipe that drips the oil into the burner.
 
Ahhh ok so it's not very well metered. The flue staying hot is very important.

Most waste oil systems use metered compressed air and a suction nozzle, plus a fan from a heating fuel unit. This way the air is metered very precisely and it is less sensitive to a marginal draft. They usually run 3%-5% excess air and are able to do it regardless of outside barometric pressure.

Drawing in outside air exclusively for combustion is a good idea.
 
If I understand correctly, you're just having it draw air from the exhaust backdraft into the shop right?

I've had issues with that the first start up of the wood burning stove each year. My advice would be to get a fire starter (those small 1"x1"x4" logs) light it, and let it chill pretty high up the exhaust. The buoyancy of the hot air will help with direction, and after a couple minutes it'll start sucking air in from your shop and out the exhaust. Then get your real fire going and it'll follow that path.
 
I bought the do-it-yourself kit from Freeburn and with that kit it comes with all the parts you need to make your own waste oil heater BUT: two 55 gallon metal drums, drum stands & heat exchangers. Which I made my own heat exchangers by cutting circles in the drum with a hole saw then using exhaust tubing to run through the drum, welding it all together when done. Keeps my non insulated 40X64 shop at roughly 50-55* when it's 20-35* outside. It's nice and toasty in the 20X20 square area around the heater though.
 
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