Uh oh
So this morning I came into work, and as I was telling my coworkers about my new tankless water heater that I just got working, a coworker came up and said that over the weekend, he had helped a friend install a new tankless water heater.
I didn't mind the one-ups-manship, but when he said that they didn't use the required Class III vent pipe, instead opting for the easy to find Class B double wall venting, and that instead of running a separate flue for the heater, he common vented it in with the furnace, I got indignant about his "damn the directions" attitude.
I asked if that was code, if he had read the directions, and if that was what they said to do. He replied "No, they said to use Class III venting" (which you can't common vent). He then went on to say that all Class III venting is just single wall tubing with gaskets inside it and clamps on the outside. And what do the manufactures know anyway, and code is overkill.
He pointed out that the existing water heater's vent doesn't even seal tightly to the unit, so why should this (completely different kind of water heater) have venting that seals tightly. When I asked him if he was a licensed HVAC contractor, he stormed away.
Well, it turns out that code exists to protect home owners from contractors that do shoddy work, and yeah, manufactures actually do know what they're talking about (and to prove it, they're willing to spend big bucks to get that UL label).
The reason you have to use Class III venting is because the high efficiency tankless water heater has a blower to exhaust the combustion gasses (and get better/hotter combustion) and that means it pressurizes the exhaust vent. Class III pipe has seals to make sure that exhaust gasses don't escape the vent and end up in your house.
The reason that you don't common vent an appliance with a blower is because the positive pressure in the venting will go out the path of least resistance, which may be another appliance and not necessarily outside the house.
I didn't even want to get into if he had installed a back draft preventer to keep the heat exchanger from freezing in our -20F winters...
And this is why home owners are encouraged to get permits and contractors do things to code. Permits are so that a knowledgeable, independent, person can double check your, or your contractor's, work. And code is there so you can feel reasonably confident that you won't destroy your brand new water heater next winter, or kill your family with incorrectly vented exhaust.
Maybe tomorrow he'll be talking to me again... In the mean time, I hope everything's OK at his friend's house.
I didn't mind the one-ups-manship, but when he said that they didn't use the required Class III vent pipe, instead opting for the easy to find Class B double wall venting, and that instead of running a separate flue for the heater, he common vented it in with the furnace, I got indignant about his "damn the directions" attitude.
I asked if that was code, if he had read the directions, and if that was what they said to do. He replied "No, they said to use Class III venting" (which you can't common vent). He then went on to say that all Class III venting is just single wall tubing with gaskets inside it and clamps on the outside. And what do the manufactures know anyway, and code is overkill.
He pointed out that the existing water heater's vent doesn't even seal tightly to the unit, so why should this (completely different kind of water heater) have venting that seals tightly. When I asked him if he was a licensed HVAC contractor, he stormed away.
Well, it turns out that code exists to protect home owners from contractors that do shoddy work, and yeah, manufactures actually do know what they're talking about (and to prove it, they're willing to spend big bucks to get that UL label).
The reason you have to use Class III venting is because the high efficiency tankless water heater has a blower to exhaust the combustion gasses (and get better/hotter combustion) and that means it pressurizes the exhaust vent. Class III pipe has seals to make sure that exhaust gasses don't escape the vent and end up in your house.
The reason that you don't common vent an appliance with a blower is because the positive pressure in the venting will go out the path of least resistance, which may be another appliance and not necessarily outside the house.
I didn't even want to get into if he had installed a back draft preventer to keep the heat exchanger from freezing in our -20F winters...
And this is why home owners are encouraged to get permits and contractors do things to code. Permits are so that a knowledgeable, independent, person can double check your, or your contractor's, work. And code is there so you can feel reasonably confident that you won't destroy your brand new water heater next winter, or kill your family with incorrectly vented exhaust.
Maybe tomorrow he'll be talking to me again... In the mean time, I hope everything's OK at his friend's house.
posted by Mark at 7:46 PM
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