Chimney questions

[warno]

My boiler is ruining a 6" double wall chimney right now I'm planning on adding another 3 feet to my 6 feet I've got now. But I'm wondering how tall can you go without added support, safely?

Also how much chimney does it take to create sufficient draft for natural draft running?

 

[maple1]

Not sure about the first question - I would likely check out install instructions from the manufacturer.

Second question, likely also depends on other things like outside surroundings & site conditions - lay of the land stuff. As well as how much draft that particular boiler needs to have for it to burn the best. But my chimney is 30' tall, and my boiler specs 0.08". It meets that spec, but I didn't do any sealing of pipe joints and I have some horizontal aspects to my stove pipe. With a better hookup and sealing, I could maybe run it with 20' of chimney. I think that draft spec is on the upper limits of usual specs, most don't need that much. Which after having said all that - likely didn't answer that question either.

 

[DAKSY]

Rule of thumb is one support for every 5 feet above the roof line.
Your appliance owner's manual should specify the MINIMUM chimney for good draft.
Over 22 feet generally requires an in line damper to prevent overdraft on wood stoves.
Not sure if that applies on your boiler...

 

[cumminstinkerer]

Daksy, He will have a hard time finding a spec, his boiler is homemade.

 

[warno]

My boiler is homemade so owners manual doesn't exist. I was just looking for a rule of thumb. I'll just add one more piece and stop there. I need the stack higher anyway.

I thought about trying it but I don't think my boiler will ever run as natural draft. I was just wondering what it would take to create sufficient draw.

 

[maple1]

You could get a manometer. Then hook it up, get a decent fire going, shut off your forced draft fan, & see what your draft reads. Or just do the whole fire building & burning thing without the fan going at all & watch what the draft does. That would tell you one side of the equation roughly - how much your pipe will pull. The other side would be - how much your boiler needs to burn right. Which you might be able to half-guess at, by watching how it's doing with the fan not going.

 

[Fred61]

The way I see it "Sufficient draft" is a moving target. It depends on location of the unit ie. is it surrounded by buildings, trees or hills. In the case of an OWB the stack is right out there in the cold. I think it's been proven that a stack provides better draft if most of it is within the walls of a structure. As a result of my experience I personally don't believe a good draft can be achieved with less than 15 or 20 feet of pipe. That would look a little strange on your unit.

 

[warno]

Ok. All good answers. Looks like i will be going with a 2 speed fan instead of single and natural draft. I'm planning to convert to induced draft from forced. My plan was to add a flue temp sensor to shut down the fan at a high set point and let it go natural. I'll just run it to switch from high speed to low speed.

Are there any cheap manometers i could look into?

 

[maple1]

Dwyer Mark II Model 25.

Not sure how the fluid would handle minus temps if it is outside though - come to think of it. That's pretty well the only one I'm directly familiar with.

 

[warno]

Dwyer Mark II Model 25.

Not sure how the fluid would handle minus temps if it is outside though - come to think of it. That's pretty well the only one I'm directly familiar with.

That's pretty good price. How does it tie into the flue? I'm guessing a small tube tied into it?

 

[maple1]

Yes. I used a piece of brake line between the stove pipe and hose.

 

[warno]

Yes. I used a piece of brake line between the stove pipe and hose.

Simple enough. I think I'll get one and add it in with my other mods this spring. Thank you.

As far as the water being affected by the cold my boiler shed is 5' x 7' and very well insulated. It stays over 90 degrees in there and up too 130-140 when firing. I don't think the water will be affected by the cold. Lol