Is a sealed combustion wh truly safe inside a conditioned space?
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Dear Home Design,
You're kidding, right? Every now and then a question comes along that makes me wonder about people attracted to green construction -- a subset of people that are suspicious of everything. You think sealed-combustion appliances may be unsafe? Then obviously atmospherically vented appliances are more unsafe -- unless, of course, the millions of Americans using these two kinds of appliances have an undiagnosed illness that is quiety sapping our health. Let's see, how shall we heat our homes? I guess there's electric baseboard, or heat pumps, or outdoor wood-fired boilers. When was life safer -- back in the old days, when we heated with a leaky wood stove in the parlor? But as I'm sure you know, old-fashioned wood stoves were not sealed combustion. Does that make them better or worse?
Martin,
I am talking about homes that are built much tighter than in the past.
Should I assume that Sealed combustion is safe because it is allowed by code?
Why do some (building scientists)say place the tankless wh's outside the home when that may increase the distance from the wh to the point of use?
I know that sealed combustion costs more for the unit and the special venting.
Home Design,
I have never heard any building scientist say that a sealed combustion appliance can contribute to indoor air quality problems. The main reason that some builders like to install tankless water heaters outdoors is to gain a little more interior space for other purposes. The biggest disadvantage to an outdoor water heater is (in most US climates) the risk of freeze damage. Tankless water heaters that are designed for outdoor installation in cold climates depend on the use of fuel (either natural gas, propane, or electricity) to keep the pipes from freezing in cold weather. Of course, that means that the homeowner pays for additional fuel -- not very green.
Martin,
Here is one source for my confussion..see number 9
http://www.taunton.com/finehomebuilding/how-to/articles/built-in-green-basics.aspx
"gas units should be isolated from the indoor air"
I suppose that "sealed combustion" is in effect isolating the unit from the indoor air?
The building scientists recommendation to place tankless or other water heaters outside the building envelope, I believe, is for a good source of combustion air. In a tight structure, expecting non-existent leakage to supply combustion air may result in all sorts of issues, including excessive carbon monoxide production and leakage into the home. If the appliance is fitted to supply combustion air to itself, as in the case of direct vent furnaces or fireplaces, for example, this problem doesn't exist.
Edited 4/10/2007 12:56 pm ET by formulaross
Formula Ross and Home Design,
Home Design's original question was about a sealed-combustion appliance. Now I'm beginning to suspect that neither Formula Ross nor Home Design knows what "sealed-combustion" means. Or else why, Formula Ross, are you explaining that "expecting non-existent leakage to supply combustion air may result in all sorts of issues, including excessive carbon monoxide production and leakage into the home"? And why, Home Design, did you quote a Web document that advised, "gas units should be isolated from the indoor air," without quoting the rest of the sentence: "Gas units should be isolated from the indoor air of the home and should draw their combustion air directly from the outside."
In case there is still any misunderstanding: a sealed-combustion appliance, by definition, draws its combustion air from outside the building.
Ignore Martin, he's having a bad day.
The answer to your question is yes, a properly installed unit is safe. Much safer than an old fashioned open air source unit in todays tighter homes.
SamT
There are three kinds of people: Predaters, Prey, and Paladins. For the life of me, I can't see why Prey feels safer from predators by disarming and emasculating Paladins.