Insulating the exhaust on my water heater?

[Toller]

I put in a high efficiency furnace two years ago. That left my gas water heater alone on the chimney.(Upstate NY) The HVAC company and the gas utility assured me that it was safe to do because the chimney was small enough, tiled, and ran up through the center of the house; but I never felt good about it. I was just too cheap to actually install a metal liner as some people recommended.

Anyhow, it seems to me that if I insulated the exhaust on the water heater (it is about 5' from the heater to the chimney) it would stay hotter and get out of the chimney without condensing better.

Does this make any sense? If so, is there any draw back to insulating the exhaust? It wastes a little energy in the winter, but saves a little in the summer, so it is probably a plus.

Thanks.

[Lawrence]

Fire hazard.

[Edwin Pawlowski]

Why? There is insulation made specifically for that use. Industrial boilers use it al the time and they have stack temps up to 600 degrees or so.

[George]

But would the "experts" at Home Depot know about it?

[Lawrence]

You ask why? Because the exhaust is hot. When things get hot they can catch on fire. In this case the proposed insulation is at risk. Fire is hazardous and is a drawback regardless of how small the risk.

Of course it can be done, so what? This guy is a homeowner. This is a water heater not an industrial boiler. He won't save any energy by doing this. He can wrap his entire heater with glass if he wants to save energy but wrapping the exhaust is something I have never seen done and don't recommend.

[cavedweller]

Didn't seem to me he cared about saving energy. Sounded like he wanted to increase his stack temperature a little bit by not losing the heat on the way to the stack. Sounded like a reasonable question to me.

As Edwin indicated, there's lots of insulation that won't burn, for instance:

[trader4]

If you read the question, the reason for doing it had nothing to do with saving energy. How could it? The stated purpopse was to keep the flue gases as hot as possible before entering the chimney, because he's concerned about the size of the chimney allowing the gases to condense. And of course it can be done, withhout any fire hazard, provided he uses the right insulation. I doubt it will make enough difference to matter though.

I've seen Toller make enough posts here to indicate he could do the job properly, without creating any fire hazhard.

[RicodJour]

I've seen Toller make enough posts that I'd worry about him setting himself on fire! =:O

T, I really don't know how much insulating the first 5' would affect the flue gas temperature. The gas is at its hottest right there so I don't think that you have a condensation problem at that point. What is prompting the question?

R

[Goedjn]

Your yearly chimney inspection will tell you whether the water is causing any problems in the chimney long before those problems become serious. If that occurs, then the appropriate solution would be to put in the metal flue-liner. Insulating the exhaust pipe between the heater and the chimney stack doesn't really solve the problem of condensation (assuming there is one).

[Toller]

Now that's not very nice; expecially since you don't even know that I routed some frame rails upside down this morning. (fortunately they are small and easily replaced.)

Exactly, the gas is hottest there, and the conductivity is highest. Since heat loss is proportional to the temperature difference and the conductivity, the gas will lose a lot of heat in those 5'. Which means it will be cooler when it gets to the chimney, and more likely to condense. I am trying to prevent that.

[Toller]

I have never heard of anyone getting a chimney inspected, outside of buying a house or having it cleaned. My understanding is that chimneys need to be cleaned once every cord or two of use. I burn about a quarter face cord a year, so I don't have it inspected very often. Are you serious?

[Goedjn]

Inspected, not necesarilly cleaned. It just means someone should climb up there at the beginning of every burning season and look for damage, blockages, dirt, wild animals, etc. If you're having to clean a wood-burner's chimney every cord, there's something wrong, you're burning crappy wood, or you're running short, smoldery fires.

[RicodJour]

No need to replace them. Finish the upside down piece and list it on ebay Australia.

You are worrying about the wrong thing. Initially, with the exposed metal flue at room temperature, the heat transfer would be the most rapid when the water heater kicks on. Once the metal flue gets to a certain temperature, the heat transfer is _much_ slower. That certain temperature will be arrived at very quickly. The flue will then only pick up enough heat to offset the heat loss to the room air. Since the heat transfer to the air outside of the flue is predominantly radiation and convection, it is far less of an efficient heat transfer mechanism than the heat loss through the metal flue where it enters the masonry. That will not change whether you insulate the ducting or not.

You already know that removing the lion share of the chimney's work - the burner output - has serious implications on the size of the chimney. Your chimney is too large and all of the insulation in the world won't change that. Condensation in the metal flue? Won't happen to any appreciable degree, and even if it did, the metal ducting is trivial and inexpensive to replace. Your real problem is the too-large, unlined masonry chimney. Condensation has far more damaging and expensive effects in a masonry chimney.

You are asking if insulating the metal ducting will help your chimney. The answer is no. Lining the chimney to the correct size based solely on the water heater output will.

R

[Edwin Pawlowski]

The risk is ZERO. No risk at all. The insulation will not burn if you hold a torch to it as it is designed to take the high temperatures of an exhaust stack. Rather than be negative, find out what is available and how to properly use it.

The man asked a question so he could find if there is a material or method that is safe. All he has to do is go to a plumbing supply house and ask about it. Comes in sizes from 4" to 36". No drawbacks as there is NO risk.

BTW, he was not trying to save energy, he was trying to get more h eat to the chimney to prevent condensation.

[Edwin Pawlowski]

Probably not, but a good plumbing supply will carry it.

[hallerb]

A camera insdpection of the interior is a good idea espically if the chimney isnt lined.

[Lawrence]

This is not about being negative. It is about being helpful. Many things are available and possible. That doesn't make it a good idea.

A bit of condensation on the inside of an exhaust flue is nothing to worry about and certainly no reason to change established safe practice. While I have already admitted it can be done, it never is. It is good and fine to learn and experiment with new practices. This does not fall into that category.

To say there is zero risk is irresponsible. I challenge you to post a link to a material specifically designed for such a residential purpose. Residential heater exhausts are never wrapped for good reasons. I have never seen it and nobody here has claimed that they have.

To call it unusual would be an understatement regardless of any theoretical scenario which may exist. The best advice in a public newsgroup is standard, safe practice not experimental scenarios which may or may not be good advice.

Toller specifically asked if there were any drawbacks. That was his question. I have stayed on topic and answered his question. Who else has done so??

[Tony Hwang]

Hmm, I'd insulate heater tank. Never heard or saw exhaust insulated.

[Lawrence]

That product is not intended for a residential market. To quote: "serving the industrial, mechanical, commercial building, and marine markets."

[Edwin Pawlowski]

Your challange is an impossible one for good reason. There is insulation made for exhaust stacks and a temperature range is given. It does not state residential, or commercial, or industrial as it works on all applications. There is no restriction for residential use.

You may be interested in this though

Unusual, yes, possible, very. In most cases you want the excess heat to heat the basement so for that reason it is not usually done. Personally, I'd not do it for t hat reason. There are other situtations in the world and I don't see anything wrong with addressing them in a proper manner with the right material.

You said there is a fire hazard. There is none.