# Any problem with insulating HWH flue? **URL:** \ **Category:** Factual Questions\ **Created:** [August 29, 2006, 10:12am UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644 "2006-08-29T10:12:46Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 10:12am UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/1 "2006-08-29T10:12:46Z")
I recently bought a water heater blanket, not so much with the intention of saving gas, but the heater is in the kitchen, and it already gets hot enough in there when we are cooking, washing, etc. The flue is galvanized steel looking stuff, 3" and runs about 3 feet to the ceiling, after which it passes though another 3 feet or so of attic crawlspace. I have a feeling the flue is generating more heat into the kitchen (especially at times when we are washing dishes or cooking and using hot water) than the heater itself, which is already insulated. Any harm in using the spare insulation to wrap the flue? Sweatingly yours, with thanks, Wanderer ---
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 10:14am UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/2 "2006-08-29T10:14:23Z")
Incidentally, it is fiberglass with a plastic wrap, and would be secured with the same high temp tape that came with the system. ---
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 10:22am UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/3 "2006-08-29T10:22:23Z")
If it is any help, I cut of a big hunk and lit it with a lighter. The plastic will burn for a moment, but appears to be self extinguishing. Burnt portions retained shape and some integrity and could not be relit. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [August 29, 2006, 1:06pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/4 "2006-08-29T13:06:31Z")
I’d be nervous about doing it. The hot water heater itself has an internal temperature of what, 140 deg F? Maybe 160 deg F if you crank it all the way up. The actual outside temperature will be a lot cooler. If I stick my hand under the insulation jacket of the heater it is warm to the touch, but not hot, maybe 110 deg F or so. The flue is going to be a lot hotter than that, the flame probably burns hotter than 1500 deg F. Depending on how much air is mixed with the gas in the exhaust the vent’s going to run 200 or 300 degrees hotter than the heater body. If I were designing the insulation for the jacket I would not make it suitable for that high temperature. They make insulation specifically for high temperature application, [here’s](http://www.sandsinsulation.com/HTML/technical.html) a chart of materials and their applicable ranges. ---
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 4:17pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/5 "2006-08-29T16:17:57Z")
Well, I went and did it, and I have been watching it cycle for a while, and nothing seems to get even melty, much less combustable. After all, the flue is the temp after (hopefully) most of the energy went into heating the water, plus it is mixed with the air coming in through the vent at the top of the tank. I would be surprised if the thing got up to 150 F. I can touch the metal with my finger and not get burned. It is just hot enough to make a space heater… ---
**Author:** ![Fir\_na\_tine](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Fir\_na\_tine](https://boards.straightdope.com/u/Fir_na_tine)\ **Post date:** [August 29, 2006, 5:17pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/6 "2006-08-29T17:17:24Z")
[QUOTE=Happy Wanderer] Well, I went and did it, and I have been watching it cycle for a while, and nothing seems to get even melty, much less combustable. . [/QUOTE] That’s the way! Experimentation will give you the answer. Wonder how many heating cycles it will take before you set the whole damn house on fire! Have someone not living in the house let us know when the funeral is. :smack: ---
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 6:17pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/7 "2006-08-29T18:17:00Z")
Monitoring temperature… Everything seems normal… OMFG! THE FLAMES! ---
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [August 29, 2006, 6:19pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/8 "2006-08-29T18:19:05Z")
Actually, everything is fine. And it is a hell of a lot cooler in the kitchen. I was more concerned about effects inside the flue, but I can’t see how preserving the heat in the flue would make it less effective… ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 7, 2017, 12:13pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/10 "2017-08-07T12:13:02Z")
I wanted to translate that spam to see what it said. It’s Arabic and it highlights _backwards_, that was really strange. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [August 7, 2017, 8:45pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/11 "2017-08-07T20:45:59Z")
The flue should already be triple wall or solid insulated after it passes the ceiling collar. Single wall flue is not legal or safe in attics. You can just extend it downward to the vent hood. Parts are available at home centers. The vent hood is the small funnel type device on 3 thin legs that mixes room air with the hot flue gases. Dennis ---
**Author:** ![Crotalus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crotalus/32/41_2.png) [@Crotalus](https://boards.straightdope.com/u/Crotalus)\ **Post date:** [August 8, 2017, 1:22pm UTC](https://boards.straightdope.com/t/any-problem-with-insulating-hwh-flue/370644/12 "2017-08-08T13:22:49Z")
> [@Joey\_P](#): > > I wanted to translate that spam to see what it said. It’s Arabic and it highlights _backwards_, that was really strange. The first paragraph says: [QUOTE=Arabic spammer] Water leak detection company in Riyadh Happy House Company The problem of water leakage is a problem that bothers many people and disturbs their lives because of these leaks of many dangers and multiple diseases. Therefore, attention must be paid to the process of detecting these leaks and speeding up the treatment before it escalates and many problems occur. Damage to the infrastructure of the house which could lead to collapse and with the company to detect water leaks in Riyadh will solve all the problems. [/QUOTE]