condensing boilers

Tom Andrews

I was presented with this question and was hoping to get some professional input on this.

Are there condensing boilers being installed out there with PVC vent pipes? With boiler temps up around 180 deg. and vent temps up around 200 deg.F, it would seem like PVC would not be an acceptable material. Are these close to actual vent temps? The closest thing I have to this is a Polaris water heater vented with PVC and the discharge pipe is getting very dark and I'm wondering about the longevity of the vent. I usually keep the water temp about 120 and the vent temp stays around 140. My understanding of using PVC was that it is very much a low temperature thing - I think I remember that CPVC was still only rated at 180. I have removed improperly installed PVC from other vent systems (hotter - Category 1) and found that at first the pipe gets pretty saggy and eventually will discolor and turn brittle. I realize that's an apples and oranges thing but what will be the end result of using PVC on a condensing boiler?

Constantin

Yup

Lots of modulating, condensing gas boilers exist. HTP Munchkin, Viessman Vitodens, Dunkirk Ultra, etc. to name a few. Reading through the install manual for a Munchkin (p.13), you can see HTP specs PVC (Type 1, Grade 1), CPVC (Type IV, Grade 1), or ABS (Class 3-2-2-2-2) non-foam core pipe for their venting (schedule 40 or 80). IIRC, Viessmann is the only one to require CPVC in the first section and PVC thereafter.

The 200 deg F exhaust temperatures you quote for a condensing unit seem to be on the high side. IIRC, I saw return temps as low as the 130degF range for condensing gas boilers. Allegedly, the Munchkin will shut itself down if the flue gasses reach 210degF (p.39) and will not allow supply temperatures above 203 deg F under normal circumstances.

But I'm just a HO, not a professional, who just happens to read an installation manual or two.

Kal Row

you have to ask yourself

if the flue temps are so high (above 136), then you are not condensing, so why buy a condensing boiler, they cost almost twice as much?

use cast iron with primary/secondary/and mixing with a tekmar 361 - it will be more efficient -

you use condensing, for cooler loads like radiant and domestic hot water, where the return water is 110 or less and you can suck the heat out of those flue gases

ps if you are going to abuse a condensing boiler - better make it a weil-mclain UTRA - from experiances on the wall, it seemms to be able to take it

Tom Andrews

Thanks guys.

Floyd_5

be careful Kal..

how you word things.....
At 180 an Ultra boiler will still be more eff. than any CI boiler out there..... It may not be the most economical choice at this point to be running at high temps., but it will be more eff.

Just a minor correction.....