# Should I insulate my water heater? **URL:** \ **Category:** Factual Questions\ **Created:** [May 12, 2002, 9:28pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688 "2002-05-12T21:28:05Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [May 12, 2002, 9:28pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/1 "2002-05-12T21:28:05Z")
I figure it would be a good idea. It’s an ordinary electric household water heater, half the normal size. It fits under a counter. Should I just wrap a bunch of pink toxic stuff around it, or what? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [May 12, 2002, 9:45pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/2 "2002-05-12T21:45:30Z")
They usually have plenty of insulation inside. Is yours putting off an appreciable amount of heat into the room? ---
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [May 12, 2002, 10:26pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/3 "2002-05-12T22:26:04Z")
Hmm… now that you ask, no, it isn’t. It’s slightly warm in spots, but that’s it. ---
**Author:** ![Swede\_Hollow](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@Swede\_Hollow](https://boards.straightdope.com/u/Swede_Hollow)\ **Post date:** [May 12, 2002, 10:39pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/4 "2002-05-12T22:39:28Z")
Insulating a water heater will help keep the water from cooling off as much as normal, thus keeping the heater from cycling on as much. This will allow the heater to use less energy. The difference may not be enough to see on your monthly bill but it will be there. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [May 12, 2002, 10:47pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/5 "2002-05-12T22:47:22Z")
When I bought one I asked the store that myself, he said they were already insulated inside., ---
**Author:** ![Swede\_Hollow](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@Swede\_Hollow](https://boards.straightdope.com/u/Swede_Hollow)\ **Post date:** [May 14, 2002, 1:00am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/6 "2002-05-14T01:00:59Z")
Water heaters are insulated, but adding MORE insulation lets them use less energy to maintain the temperature of the water. The current issue of Consumer Reports recomends adding insulation to water heaters and insulating the hot water pipes to save energy and save water (the water in the pipes won’t cool off as much so the water at the tap will warm up faster, you won’t have to let the water run to get hot water all the way from the heater to the faucet). ---
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [May 14, 2002, 1:32am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/7 "2002-05-14T01:32:21Z")
Hmm… insulate the pipes, ey? I just gotta insulate something, I just gotta. Thanks for the responses, and thanks in advance if there are any more! ---
**Author:** ![glilly](https://avatars.discourse-cdn.com/v4/letter/g/48db29/32.png) [@glilly](https://boards.straightdope.com/u/glilly)\ **Post date:** [May 14, 2002, 2:06am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/8 "2002-05-14T02:06:20Z")
I would insulate if the outside of the WH feels warm. It is possible to overinsulate! The equation for heat transfer out of a cylinder shows heat loss being based off of thickness of insulation but also radius^2. As you add insulation, the extra insulation slows the rate of heat Xfer, but the increased diameter (and therfore heat loss surface) increases. At normal thicknesses, extra insulation slows heat xfer, but since the factor is r^2, at some point it “catches up” with the extra insulation, after which more insulation will actually make the thing less efficient. I haven’t done the calculation, but I suspect you’d need a shitload of insulation to get to that point. If you can’t feel a warm exterior, it may not be worth the insulation. But doing the pipes is a good idea. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 14, 2002, 2:06am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/9 "2002-05-14T02:06:27Z")
also throw a little insulation on the inlet pipe - maybe a foot or so ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [May 14, 2002, 2:19am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/10 "2002-05-14T02:19:35Z")
Also, make sure that the P&T valve isn’t obstructed. This is the pressure relief valve for the heater; it keeps the heater from exploding if the pressure gets too great inside (admittedly, it rarely happens, but you can’t be too safe.) If this was a gas water heater, you would also have to keep the insulation away from the inlet and the exhaust flue. ---
**Author:** ![biker](https://avatars.discourse-cdn.com/v4/letter/b/ce7236/32.png) [@biker](https://boards.straightdope.com/u/biker)\ **Post date:** [May 14, 2002, 4:34am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/11 "2002-05-14T04:34:16Z")
it is a good idea, saves you some money for very little cost. many stores sell a blanket of insulation, made especially to fit around water heaters, almost like a coat. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 14, 2002, 11:36am UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/12 "2002-05-14T11:36:16Z")
Also most manufactures say don’t insulate the H.W.H. and it will void the warnentee if you do. also I think **cornflakes** ment the air intake when he said the inlet - the inlet water pipe should get a little or else it acts like a cooling fin for the tank don’t obstruct the overpressure valve ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [May 14, 2002, 12:05pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/13 "2002-05-14T12:05:55Z")
Insulation is so cheap anyways, you may as well if you can feel any warmth at all. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [May 14, 2002, 3:02pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/14 "2002-05-14T15:02:19Z")
Sounds like a plan but I don’t have any room to put a blankie on it. It sits right here in my living room, so any heat coming from it warms the house 🙂 ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [May 14, 2002, 4:48pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/15 "2002-05-14T16:48:32Z")
> [@](#): > > \*Originally posted by k2dave \* > **Also I think cornflakes ment the air intake when he said the inlet** Right. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 14, 2002, 8:05pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/16 "2002-05-14T20:05:19Z")
**so any heat coming from it warms the house 🙂** then the only time it will help you (to insulate) is in the summer if you have a/c in that area. Also it will help a little if you use lets say an electric hot water heater and oil furnace since oil is cheaper. So lets get the details: what fuel is you hot water heater? - you said electric what fuel do you use to heat you home? do you air condition your living room in the summer? if not does it give off ‘too’ much heat in the summer? does it give off too much heat in the winter? if the waste heat is actually used to heat the room then it’s not lost. ---
**Author:** ![billy](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@billy](https://boards.straightdope.com/u/billy)\ **Post date:** [May 14, 2002, 8:20pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/17 "2002-05-14T20:20:58Z")
These water heaters are tested by UL when used as the manufacturer instructed. If the manufacturer says not to insulate, DO NOT INSULATE. Part of the certification process involves verifying that wiring and other electrical insulation is not over heated. Adding insulation to the outside of the heater creates the risk of burning insulation off wiring internally and possibly starting a fire or creating a risk of electric shock. Or less dramatic would be buring open the thermal protective device that would permanently disable the heater. Trust the manufacturer, they would not bother printing the instruction not to insulate unless they had a real reason. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [May 14, 2002, 8:47pm UTC](https://boards.straightdope.com/t/should-i-insulate-my-water-heater/108688/18 "2002-05-14T20:47:03Z")
From the [Department of Energy](http://www.eren.doe.gov/erec/factsheets/eewtrhtr.html): > [@](#): > > When you turn on a hot-water faucet during cold weather, it may take several seconds for the water to become hot. This happens because the water travels through pipes from the water heater to the faucet, and some of the pipes may pass through unheated sections of the house, such as the basement. As a result, the hot water loses some of its heat to the surrounding space. > > This heat loss can be reduced by insulating hot water pipes wherever they are accessible—especially in unheated areas. Use quality pipe insulation wrap, or neatly tape strips of fiberglass insulation around the pipes. Eventually the water will cool, but it will remain warmer much longer inside insulated pipes. > > Insulating your water-heater storage tank is a fairly simple and inexpensive improvement that can help maintain the water temperature at the thermostat setting. **Some newer models of water heaters are well insulated and do not need an added layer, but a heater that is warm to the touch needs additional insulation.** > > Easy-to-install, pre-cut blankets (or jackets) for electric water heaters are widely available and range in cost from **$10 to $20.** Your local utility company may offer them at a lower price, give you a rebate, or even install them at no cost. **When properly installed, a water heater blanket on an electric water heater will pay for itself in energy saved within 1 year.** Installation is more difficult on gas- and oil-fired heaters. Ask your local furnace installer for instructions. > > If your water heater is at least 7 years old, you should carefully evaluate your water-heating needs and investigate the types of heaters that could replace your current one. Although most water heaters last 10 to 15 years, early investigation and timely replacement can ensure a wiser purchase. For more information on replacement, see Selecting a New Water Heater. [bolding mine] Looks like insulating the water heater is a good bet.