2” vs. 3” diameter pipe for exhaust vent and intake?

[NY_Rob]

I'm finalizing the parts list for my upcoming HTP UTF80 mod-con install.

I'd rather go with 2" Schedule 40 PVC for the intake and exhaust piping vs. 3" PVC because it would make installation and routing easier if possible.

My exhaust and intake pipes would exit the boiler, go about 1' straight up to a 90o elbow then 4' straight to the outside wall of the basement to a no other elbows, 45's, etc.

Total combined straight pipe run for intake and exhaust: 10'
Total 90o elbows: 2 (one in/one out)
According to the HTP UTF80 install manual -you don't include the first elbow in the piping length calculations.

Here's a section of the official HTP UTF80 install manual regarding piping:
This boiler uses 2” or 3” diameter pipe for exhaust vent and intake pipe.

ALLOWED COMBINED VENT LENGTHS:
2” COMBINED VENT LENGTH- 50’
3” COMBINED VENT LENGTH- 100'

NOTE: When using more than 1 elbow, reduce maximum allowable length:
5 feet (1.5M) for each additional 3” 90o elbow
2.5 feet (.75M) for each additional 3” 45o elbow
8 feet (2.4M) for each additional 2” 90o elbow
4 feet (1.2M) for each additional 2” 45o elbow


So my question is.... is there any disadvantage in using 2" Schedule 40 PVC vs. using 3" Schedule 40 PVC for my install considering the short runs installed?

Any comments are appreciated... thanks!

 

[Leon82]

Seems like your well within the 50 feet for 2 inch. Smaller hole to drill

 

[Sponsor]

 

[Leon82]

There may be a warning in the manual about using cpvc for the first few feet of exhaust venting also.

I had planned a nice short run like yours but the manual wanted a 12 ft minimum run for the WHN.

 

[NY_Rob]

Thanks Leon,

That's what I was concerned with- I've looked at several different mod-con install manuals while researching boilers- the Triangle Tube Prestige 60/110 for example specifies:
"In 2 inch PVC vent applications, the first 7 equivalent feet of the vent system must utilize CPVC material."

The boiler I'll be using- HTP UFT80 the manual specifies only that:
"The included 6” length of 3” CPVC pipe MUST BE INSTALLED in the exhaust vent connection BEFORE venting the boiler."

and

"This boiler uses 3” diameter adapters for exhaust vent and intake pipe. In order to use 2” pipe, it is required to reduce pipe size in a vertical length of pipe with a reducing coupling (not included)."

So it seems that as long as you use the "The included 6” length of 3” CPVC pipe" for the exhaust- that covers the CPVC requirement... and the the 3" to 2" Schedule 40 PVC adapter must be placed after the 6" CPVC pipe and "in a vertical section" to prevent condensation buildup/pooling.

For the HTP UFT80 There does not seem to be any "minimum piping length" requirement (which I have seen in other mod-con install manuals) though....

 

[NY_Rob]

Figured I give HTP tech support a "try before you buy" call.... they picked up within 10 seconds- impressive!

Tech said there is a minimum length requirement of 13' with 3" pipe, even less with 2" pipe- so my 8' run plus two elbows would exceed the minimum requirement for 2" piping.
So it looks like it's a go for 2" intake/exhaust piping....