Buy 2 blankets and combine them to fit your water heater.

I can remember back in the late 50s and early 60Âs when fuel was cheap the water heaters were operated at 180degF and they had no insulation or external jacketing. In those days there was a great concern that people were accidentally bumping up against the water heaters and receiving severe burns. The standards were then amended requiring that all water heaters must have a minimum of ¾" of fiberglass insulation, a sheet metal jacket and under no circumstance could the external temperature of the unit exceed 140degF under normal operation.

During the first fuel crisis in the mid 70Âs people were encouraged to install additional insulation blankets to reduce the standby losses from the water heater, however it was soon realized that if an insulation blanket is improperly installed it interferes with the normal function of the water heater thermostats and temperature & pressure relief valves causing very erratic temperatures and in some instances creating safety issues. In addition, quite often when the insulation blankets are improperly installed they interfere with the normal flow of combustion air and result in very high levels of carbon monoxide.

In the late 80Âs the plumbing codes were again amended requiring that ALL water heaters must now have a minimum of R-12 insulation.

REF:
International Residential Code IRC-504.2.1(en)
Uniform Plumbing Code UPC-150(j)1A(c )
The codes specifically sayÂ"No external blankets required"

Many local codes have amended that wording to say "External Blankets Prohibited".

In my jurisdiction there is a $50 fine for even selling a water heater blanket.

In order to meet the new insulation standards most water heater manufacturers have discontinued the use of fiberglass insulation and they now use cast in foam insulations, which often far exceed the required R-12 minimum

Everyone seems to be fixated on the supposed high energy wasted to standby losses from a tank type water heater, but in reality such is not the case.

Two years ago our plumbing apprenticeship class, in co-operation with the local gas company and a number of local hardware stores, appliance dealers and plumbing suppliers set up a project to test the actual cost of water heater standby losses.

Twelve different makes and models of residential contractor grade 50gal gas tank type water heaters were installed in an unheated warehouse. All 12 units were fed from a common water line and each water heater is supplied through a separate gas meter. Each water heater is then fitted with one line on the output side that terminates into a keyless hose bib beside the unit, thus there is no demand from these water heaters therefore they represent standby losses only.

The water heaters were then filled and left standing with the thermostats set at the code maximum of 120degF. Every month the gas meters are read and the fuel cost is computed at the standard residential rate for this area. After two years of following this project it has been determined that the monthly average standby loss is $5.02. (The worst case in the test is averaging $5.87mo.)

I might add that two of the water heaters in this test have specific wording in their installation manuals that states the addition of an insulation blanket will void the warranty.

Wow, we've had this debate before:

Regardless of what the code says, there are a significant number of water heaters that can be purchased-- and I am sure are purchased-- that have less than an R12. If people weren't buying them, virtually every manufacturer wouldn't be selling them.

Here are some of the heaters with a R-8:

State Water Heaters
http://www.statewaterheaters.com/lit/spec/res-gas/SRGSS01206.pdf

AO Smith Water Heaters
http://www.hotwater.com/lit/spec/res_gas/ARG-SS01406.pdf

Whirlpool at Lowes
http://www.lowes.com/lowes/lkn?action=productDetail&productId=188421-135-BFG1H5040T3NOV&lpage=none

What's more, there are millions of water heaters that have been installed for a while that are less efficient than what's being sold now.

Now, improperly installed blankets could potentially cause a problem -- as could anything else improperly installed. Installing a water heater itself improperly could be hazardous-- surprisingly some local codes haven't banned water heaters. That said, if a heater manufacturer says not to install a blanket, I would take it at its word.

Standby losses of ~$60 a year aren't something to dismiss lightly. That is about 10% of my total annual gas bill.

Look, just as we look back and are appalled at the waste of the 1950's and uninsulated water tanks, we are going to look back and be dumbfounded at the foot dragging and FUD around tankless heaters and better insulated tank heaters -- and that's exactly what this is--foot dragging and FUD.

I am all for manufacturers making more efficient appliances and codes actually requiring them and those codes being enforced-- but until then, water heater blankets are a cheap, safe way to significantly reduce the standby losses on water heaters.

That standby loss seems extremely high to me.

Gas water heater with standing pilot light, 2 person house, empty nesters.

summer use gas is only for water heater and is 3 to 6 CCF at just under a dollar per CCF plus of course the 8.80 customer charge which you pay even if you didn't use any gas. Actual water heater gas cost is $3 to $6 a month.

I measured mine and get a loss of 280BTUH which turns out to cost about $9 a month or $108/yr assuming oil at $3/gal. DOn't know if that's enough for me to get one.
By the way,in doing the calculation, I measured the surface temp of the HWH and got 85 deg with a room temp of 70 (water temp at 150) , so the insulation I have is nowhere near the required. If it were R=12 then my surface temp would have been about 7 degrees hotter than the room; mine was 15.

Keep in mind that in the winter the incoming water is usually quite a bit colder--that may be reducing the response.

I know that in our house to get a pleasant shower temp in teh winter requires almost all hot/no cold, whereas in summer one needs very little hot and mostly cold faucet on.