Replacing furnace vent

[R Clark]

Our house is 16 years old.  Sided with Hardie Plank.   We are getting ready to repaint the house.  When the painter and I were walking around he house the other day, I noticed trouble at the furnace vent.  The Hardie board at that location is getting soft and warping.  I believe it's due to the warm moist air constantly being blown out on it during the winter.

The furnace is actually a propane aux burner under a heat pump.  It's two seasons old and replaced an all-electric unit that was original to the house.  I'm surprised the Hardie plank failed so quickly in this instance.  

Picture:

[attachment=27215]

I have some plank with which to make the repair.

I want to figure out a new solution for the vent, and get it further out from the house.  Can I do that with a simple extension glued on to the PVC?  Should I consider another routing?

I haven't pulled this apart, yet, so I guess I could find a poor job on the vent install caused the failure. 

Any thoughts are welcome.  Thanks in advance.

[barnowl]

I have a vent that looks like this on my Lennox system. It can be extend out further than the one at your house. 

Works well.... and I have vinyl siding. Other manufacturers offer it as well.... But be sure it's above any expected snow height.



https://www.homedepot.com/p/Rheem-3-in-P...lsrc=aw.ds

[TDKPE]

I've also seen two pipes exiting the side wall, one for hot discharge and the other for intake air.  No combination cap like in the OP's photo.

It almost looks like the intake and exhaust are reversed in the OP's photo. The hot stuff should be streaming rapidly from the cap through that visible grill, and not cause any issues with the siding.

[Roly]

I've also seen two pipes exiting the side wall, one for hot discharge and the other for intake air.  No combination cap like in the OP's photo.

It almost looks like the intake and exhaust are reversed in the OP's photo.  The hot stuff should be streaming rapidly from the cap through that visible grill, and not cause any issues with the siding.

 +1   Check which is intake and which is exhaust before replacing in the same orientation.  The side that looks the worst is probably the exhaust pipe but as Tom said the grill should be on that side and not the intake.   Roly

[brianwelch]

I might consider an aluminum backer plate on standoffs so ambient air can circulate behind...

[R Clark]

Thanks all.

The vent piping is all visible from the basement to the exit point on the sill.  I had not thought to double check that the installers had the right pipe going to the right hole.

The vent is not above the expected snow line.  This is Iowa, we can expect more than four inches of snow every now and then. Happened last in early April.

I think I want to install a "snorkel" type configuration and get it up and away from the house.  That's what we had at our previous place in town.

[blackhat]

Either someone screwed up the connections (reversed) or there is a bad connection on the back of that vent termination.  No matter as it is supposed to be extended above the expected snowline.  Get an install manual for your furnace, online if you don't have the paper copy, and study the section on venting,  Usually they have illustrations showing permissable vent terminations.  If not, give a shout and I'll find some for you.

[R Clark]

Either someone screwed up the connections (reversed) or there is a bad connection on the back of that vent termination.  No matter as it is supposed to be extended above the expected snowline.  Get an install manual for your furnace, online if you don't have the paper copy, and study the section on venting,  Usually they have illustrations showing permissable vent terminations.  If not, give a shout and I'll find some for you.

Thanks.  I have the installation guide (LOML has catalogued all of that stuff in three ring binders.)  In reviewing the material, I see that the installers did not follow instructions for the snow line (book calls for 12" clearance above the expected snow line).  I also think that the flush mount termination cap, while unobtrusive, is likely not a good choice for this application.  I'm thinking I'll just do a site-built vent pipe arrangement that meets the install guide spec.

The other half of this issue is the penetration through the siding.  So, I spent some time on the James Hardie site this morning.  Their install instructions call for:

"Any vent piping is required to have blocking and flashing at the penetration. A block of 5/4, 4/4 HardieTrim® boards should be installed around the point of penetration. The blocking should extend 76-100mm (3-4 in) along the wall from the edge of the vent. To install a block around an existing vent, it may be necessary to cut several blocks, with weather-cuts on each piece. Flashing must be installed over the top of the trim block."

I won't use Hardie Trim for the blocking; I'll just use 1" thick PVC trim boards available at the big box.

[R Clark]

"Welp.  There's yer prahblem."

Took the cover off the vent, and this is what it looked like:

   

There was no seal between the exhaust vent pipe (still in the exterior wall) and the vent termination fixture.  Given that there's a restricted exhaust port in the termination assembly (which is allowed in the spec for this unit), the fact that there was no seal means that a significant amount of  the exhaust gas was being forced back onto the siding.  This went on for 2 1/2 winters.

As you can see, the Hardie Plank is disintegrating at this point.  It turns to powder when touched.

The affected area does not appear to be very large at this point.  I can't tell if the siding plank underneath the rotted plank has been affected.  If not, I think I'll just cut out the bad siding, and install a PVC block in its place, with Z flashing between it and the plank above it.

[blackhat]

Have you spoken to the installer?