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Concentric Vent modification.

djc2232 Member Posts: 136
Wondering how I can achieve greater height off roof with my concentric vent for my Modcon boiler. its currently 14in from roof to bottom of rain cap where intake air goes in. My boiler manual states I can go as high as 20in above roof line. Now what I think ive read is that theres no way to cut the concentric kit (above the elbow where the two pipes join) and extend it for safety reasons. As in cutting the inner and outer pipes and attaching longer lengths. I will post pictures when lighting is better but i looked in my attic where it runs and theres not much length left until it hits the joint section where both pipes converge. I may be able to extend it that way. Reason for it is that where the vent terminates i get realy bad snow drift in the winter. Just want a little more insurance so i dont have to climb up there late at night because it got clogged. I have a tall ladder and rake i used last winter.

So what is the best way to modify? Cut concentric up top and add pieces there. Leave the concentric whole and extend as high as it will allow till the joint reaches bottom of roof.

Other options which i really dont want to do but run two separate for intake and exhaust, that way id be able to go to max height as listed in manual. But then id have to re seal original hole from concentric.

Also, sidewall is a no go. Soffit overhang is too far and where boiler is mounted in the house doesnt allow for an easy run.


    HVACNUT Member Posts: 5,023
    They do make extensions. Call the manufacturer. I'm not sure but I believe PVC you provide must be sch 80.
  • djc2232
    djc2232 Member Posts: 136
    What Ive found per manual (Weil Mclain) is that by no means should the actual concentric portion be cut and modified.

    I have an HVAC company coming in to do the modification soon. Basically going to cut both intake and exhaust pipe just below the concentric vent. Then add length of pipe to extend the vent up about 6 more inches. Still under max height per manual.

    That was pretty much my idea from the start. Normal 3in PVC coupling then sealed should work.
  • ch4man
    ch4man Member Posts: 294
    have a care. a coupling on the inner pipe will reduce the clearances between the inner and outer pipe thereby choking off the combustion air......
  • djc2232
    djc2232 Member Posts: 136
    The concentric portion isn't being modified. Just below it is where the cuts will be made.
  • SeanBeans
    SeanBeans Member Posts: 506
    These pipes are already connected to the boiler?

    Because you can cut below the concentric and perhaps push the concentric kit up higher thru the roof and then pipe your exhaust and intake back to it
  • djc2232
    djc2232 Member Posts: 136
    Yes. Boiler has been in service for 2 winters now. That's the plan. Cut intake and exhaust below concentric pipe and extend up as high through the roof as possible. Hopefully at least another 6 in. The. Couple both back together.

    There's no option to vent sidewall due to boiler location and the fact my vented soffit is about 2.5 feet.