Power Vent Water Heaters

12/20/07   Allied Plumbing Services, inc.

I've noticed power vent water heaters are becoming more and more popular these days. It seems like everyone’s asking about them lately, so I thought I would take some time here and clear up some common misconceptions. Compared to a standard (conventional flue type) water heater, a power vent heater is no more efficient. They both run at about 80% efficiency, use the exact same BTU’s, and the recovery rates are almost identical. The warranties are also the same across the board. That’s pretty much where the similarities end…

The differences are what I want to address here. As I said before, the BTU’s are the same so no change on the gas bill. The power vent does, however, require electricity to power the fan which will show up on your electric bill. In a sense, making it less energy efficient than the “standard” heater. Not to mention, in the event of a power outage your left taking cold showers. The power vent also has more moving parts and electronics that can eventually fail as well. The other difference, and to some the most important, is cost. The power vent model is typically 70 to 80 percent more expensive than a standard model heater. Once you factor in the additional labor to run the PVC flue and electric the price difference can be quite significant.
There is one more difference between the two, and to me probably the most important. Homes are being built more “tight” now than ever before, meaning less outside air infiltrating the house.  On the surface that sounds like a good thing, and it is as long as your home has the proper amount of make-up, or combustion air. There’s quite a few things in a typical house designed to remove air from the home. Bathroom exhaust fans, vent hoods in kitchens, furnaces, fireplaces and clothes dryers are great examples. You can also add power vent waters heaters to that already long list. The air that these items remove needs to be replaced from somewhere otherwise the home will experience a vacuum, or negative pressure. Once this happens, a back draft is created causing carbon monoxide and other dangerous gasses to be released back into the home. Just this morning while doing some research for this piece, I read a story about a young boy who died while sleeping on the floor in front of the fireplace in his home. His house experienced negative pressure and the carbon monoxide gasses from the lit fireplace back drafted back into the home, killing him as he slept. I’m certainly not saying a power vent water heater caused his tragic death, but  it is one more thing in a home that will remove air. Varying with vent length, a 75 gallon power vent water heater will rob the room of air at the rate of about 40cfm (cubic feet per minute). That doesn’t sound like much, but in a full cycle that will be about 1600 cubic feet of air. That’s enough to fill a room 14’ x 14’ x 8’ tall. Replacing all that air is something that needs to be thought about.
I know this comes across as me bashing power vent water heaters. To be honest, it makes no difference to me whether they’re used or not. I just wanted to clear up some of the misconceptions out there.





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