Venting Question

[John Molyneux]

Dear experts: Now that you guys (well, Dana in this case) have helped me figure out heat loss and boiler size I have a venting question. I won't be able to use the location of my existing sidewall vent for the new boiler since we're putting in a screen porch and deck in that area. I have differing opinions from contractors and manufacturers about the best alternative.

Our preference would be to go up the chimney and use either of the two currently unused flues as a chase. The other flue, however, sees regular fireplace use. Could there be temperature problems, e.g. too hot to use an adjacent flue as a chase? Is there a work-around that makes sense?

I'm also wondering if there might be a problem with the intake air picking up fireplace combustion byproducts. If that's the case, is it OK to draw intake from sidewall and vent through chimney, in which case they would be different lengths?

An alternative would be to exit at the existing location and then run it vertically up the sidewall until we get enough height, consistent with other code offsets, etc. Would there be any temperature or other issues running 10-15 feet of exposed exhaust vent up an outside wall? (Design day temp is +2F.)

Another alternative would be to run it up inside the outside wall, which could be a PITA.

Thanks in advance.

 

[BadgerBoilerMN]

In reality either will work but each manufacturer has their appliance tested with different materials and techniques. Their equipment then must be installed as tested. We often use these limitations in determining the which boiler is best. We use several that allow terminals on different load planes.

Conventional chimneys are inefficient relics and should be eliminated in any deep energy remodel. But if you must have a chimney it makes a great chase for a direct-vented boiler. We like to use a chimney as chase with a coax venting system, especially since it allows the preheating of combustion air, improves the air quality, and eliminates the possibility that the vent plume will obstruct your view from window or take the paint off the house if installed poorly.

As for use one side of a double flue. If they are both tile lined I have never seen a problem with this. We use PP in most of our applications and coax makes the chances of elevated temperatures being a problem nearly impossible. Cross contamination is a concern best addressed by careful application, installation and experience.

When in doubt/ignorance, the local inspector and distant manufacturer will naturally steer you away from the unconventional.

 

[Sponsor]

 

[John Molyneux]

In reality either will work but each manufacturer has their appliance tested with different materials and techniques. Their equipment then must be installed as tested. We often use these limitations in determining the which boiler is best. We use several that allow terminals on different load planes.

Conventional chimneys are inefficient relics and should be eliminated in any deep energy remodel. But if you must have a chimney it makes a great chase for a direct-vented boiler. We like to use a chimney as chase with a coax venting system, especially since it allows the preheating of combustion air, improves the air quality, and eliminates the possibility that the vent plume will obstruct your view from window or take the paint off the house if installed poorly.

As for use one side of a double flue. If they are both tile lined I have never seen a problem with this. We use PP in most of our applications and coax makes the chances of elevated temperatures being a problem nearly impossible. Cross contamination is a concern best addressed by careful application, installation and experience.

When in doubt/ignorance, the local inspector and distant manufacturer will naturally steer you away from the unconventional.

Coax meaning double wall with exhaust on the inside channel?

 

[BadgerBoilerMN]

Correct.