Improving draft

I have an outdoor boiler and I want to improve the draft in the stack. When I open the door to load, I get quit a bit of smoke back at me and want to see what I can do to make that better. The system itself is fan assisted when the system calls for heat, so it's not necessarily a performance issue although there are many benefits to improving the draft.

Now, I know there is a lot that goes in to what creates draft within a system, but about the only thing I can change is stack height. Stack is 8". I currently have about 7' of pipe above the boiler. I'm wondering if someone has a way of calculating how much stack I actually need to make a difference.

My assumption is that a little should go a long way just given percentages. If I add 3' to an already 7' stack, I'm adding 43% to the overall height. But, id rather not be spending $100-$200 on insulated sections when the actual difference won't be enough to justify the expense. Make sense?

Can anyone offer any advise?

 

For an outdoor wood boiler, why would you care about smoke upon reloading from the door?

But even so, you shouldn't need double wall if you want to extend the height.

 

Increasing draft has a lot of be benefits, with one being less smoke from the door after opening. I agree that since it's a boiler, it's less of an issue, but I'd still like to increase the draft if I could. Loading can be difficult at times, especially when you don't want to smell like smoke the rest of the day. Better overall combustion is another concern.

 

The chart near the bottom of the page gives insight into stack height and temperature differences driving your draft.

The Hearth in the House as a System

 

Can you just use cheap single wall pipe? At least for testing? Nice not to have to worry about chimney fires. Taller flue might also carry the acrid smoke farther away before it gets down to eye level.

 

I say you redneck engineer it.
Just buy and add one peice of pipe at a time untill desired effect is reached!

 

Definitely use a test pipe, single wall before a purchase of $100 or more.

I don't know why you want to improve the draft; just for reloading purposes?

Backwoods Savage I always cover my stack during the period it is not in use....but I never cover the masonry chimney on the house

 

I'm with the school of thought that the stronger the draft, the quicker the burn.

Feel the burn yet?

 

4 OWB's around me and we all have caps.

 

Yes, it will increase the amount that it will burn, and depending on the boiler, they already go through a lot of wood.

 

Since it is fan assisted, is there a way to add an override switch to run the fan while loading? Better yet, use a timer so that you won't forget to turn the override off.

Excuse my suggestion if it is ignorant, I don't know anything about OWBs.

 

Not ignorant. The fan is located in the door so that's not possible.

 

OK, one more ignorant suggestion, if a pipe extension won't work for any reason (it should be the first thing to try), you could add a draft inducer on a timer.

A couple of options here: Room to Room Fan : Crawl Space Ventilation : Dryer Booster Fan : Tjernlund Products, Inc.

 

It seems like we could add a mousetrap in here somewhere ...

 

Maybe a pre-dryer for the wood?