Outdoor furnace chimney draft

hot_rod

In certain areas around here I see an additional 5- 10 feet added to encourage a draft. You may need to "guy" the flue if you go up above very far.

Also taller chimneys helps keep some smoke from your windows. And the neighbors.

I wouldn't recommend reducing the size!

hot rod

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Nevin

How do I get draft in an outdoor furnace chimney?

I've seen some owners wrap fiberglas around the short metal chimney.
Does anyone have any experience using a smaller pipe (with both ends open)
inside the larger pipe. The small one should get hot and increase draft up the chimney.
Any other ideas?

Thanks,
Nevin

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Steve Bergerson

Add more pipe

Are you having trouble getting a draft when the stove is running? Does it have a draft motor? Or are you looking to keep smoke out of your eyes when you load the stove?

I added an additional 4 feet of pipe to my outdoor wood boiler. It helped tremendously in keeping the smoke from "rolling out" when the door was opened for loading.

If your stove is not drafting properly when running with the door closed, you may have to clean your flue paths.

Steve Ebels

Draft problems

This is one of the most vexing problems with an outdoor wood fired unit. When you add more pipe you create other problems. If you don't add length, you put up with a face full of smoke when fueling the unit.

Adding pipe creates a sometimes horrendous creosote problem. These things typically don't have enough stack temp to keep the chimney clean when additional pipe is added. I've seen them plug off in a matter of days with only 5 feet added. Reducing the pipe size would not be advisable. Most of these units are fan forced draft so you dont need "draft" per se.

If you follow some of these "rules" for installation you can eliminate most of the problems.

Locate the unit a minimum of 50 ft away from a structure. Downwind as far as what direction the prevailing wind is from.

Face the loading door into the prevailing wind direction.

Always let the fire die down (shut the draft blower off a minimum of 15 minutes before fueling).

Always use seasoned wood. Cut, split and stacked for at least a year. Some of the companies that manufacture these claim they will burn green wood. This is true, BUT you expend a lot of available btu content just burning off the excess moisture in the wood and create gobs of smoke in the process.

We have had very few complaints when these guidelines are followed.

Dan Peel

a little more information

If you must add length to an outdoor wood furnace chimney - use insulated sections. Once the heat is past the exchanger it is of no use to you - force it to heat the chimney section to create draft. Passive draft units benefit more from chimney length than blower draft units.
The fill door is several times larger than the chimney vent and smoke is almost a lazy as water. Your best "smoke in the face" avoidance is to let most of the fuel get used up before refilling.
Dan

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