water heater blankets


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Old 01-06-04, 04:46 PM
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water heater blankets--what else to minimize heat loss

Does anyone have a feel for how much fast heat is reasonably lost in a water heater?

Before we left town for 3 days, I turned down the water heater thermostat to vacation mode, and I shut off the water main (in case something blows up and floods the whole house). When we got back, there was simply no hot water. It was ice cold.

We have this mammoth 75gallon water heater in the garage that came with the house. [There's no way our household needs so much capacity. But that's a different problem.] It supposedly has R-16 insulation in it and it has an R-10 rated blanket around it also. For kicks and grins, I just replaced that R-10 blanket with a R-19 aluminumized foil version from Home Depot. (I don't expect it to do much difference. It just has this ugly silver color instead of the usual white and has the texture of some heavy carpet padding instead of the usual fiberglass fill)

I would 'think' there would be some heat retention value in it. I know for a fact that the heater fires up at least once or twice a day even if nobody's been using hot water. This seems like a total waste of energy just keeping a tank of hot water around... a lot more than what the tankless heater guys hint at.

Anything else that can be done to help efficiency? Seems like a bit of heat goes up the flue no matter what, as well as the pressure relief valve and inlet outlet pipes (which I've insulated)

I guess this is just the way it is...sadly...

thanks
 
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Old 01-06-04, 05:16 PM
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I'll upset a few energy freaks here. I think a WH blanket is a waste. The main reason for this is what most people don't realize is there's a BIG hole up the middle of the heater in a gas application. You always have that chimney effect even when the burner is off. Do you really think adding a blanket to the outside (where there already is insulation) is going to keep the water warmer? Feel the outside of your heater, is it hot? Mine isn't. Would you need more insulation over a cool/cold heater?

Having a heater in an unheated garage will work harder obviously. A guy would do well to move the WH to a heated portion of the house. At least you aren't fighting freezing weather shooting up the pipe...think about it.
 
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Old 01-06-04, 05:20 PM
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What is this "vacation mode" you used? What temperature does it try to maintain? If it's set to only prevent freezing, you had a lot of water to reheat when you turned it back up.

What's the ambient temperature around your water heater? Heat loss is a function of the temperature differential between the hot water and the surrounding air. The greater the difference, the faster the water cools down (and the more frequently the water heater has to run to heat it back up again). No amount of insulation completely stops heat loss. It only slows the rate at which you lose it.
 
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Old 01-06-04, 08:44 PM
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Hello: A. Lung

Read your question several times searching for a specific clue. I also read the replies, which provide many good possibilities and agree in part with webrebel.

If the outside of the tank does not feel warm to the touch, the added blanket provides little in the way of additional insulation to prevent further heat loss. Nice decorative cover...

Heat loss through the vent flu in nominal. Downwards drafts from the vent pipe are diverted by the down drift diverter. Upward drafts are nominal also, especially if the location of the tank is not in a windy or drafty area. The garage location would not meet that criteria. Thus, we need to explore other possibilities.

A circulating pump possibly? Used to keep hot water readily handy at the faucets maybe? A bathroom spa tub? The circulating pump used to keep that water warm?

Tanks of that size used in smaller homes may be all or part of a hydronic heating system maybe? Used for the space heating system of rooms. Is your home heated with such a system?

Turning the incoming water to the entire house elliminates the hot water leakage theroy. Climate zone not to critical. Nor was 3 days in the vacation setting nor tank location.

Pondering the possibilities. Temperature drop should not have caused "ice cold" water after 3 days. Cooler water temp yes but not ice cold. Vacation setting is well above freezing or ice cold.

Something of importance missing. More details would be helpful. Use the reply button and if possible at more specific details pertaining to what is in the home, it's heating system, a circulating pump in the hot water system, etc.

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Old 01-07-04, 11:02 AM
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Hi guys,
thanks for the responses... Yes, I need to clarify some of the 'subjective' comments I made :-)

'Ice cold' was somewhat misleading. 'Ice cold' water to me is standing there in the shower stall with anything less than about 70F raining down my body in the shower. I didn't actually take a thermometer and see how warm/cold it really was though :-)

Heater sits in an unheated, insulated garage, but one that is vented with outside air. It's been "cold" (relative to San Jose standards which means high 30's/low 40's at night and 50's during the day) so the temperature difference between ambient and what we set the thermostat is a fairly good differential.

We're not running the heater on the 'scald' setting.. We have it set just high enough to keep the wife from complaining which is the low 100's--but definitely not way up in the 110+'s.

We have a recirc pump--which to me is a dumb idea. If anything I have it on a timer for about 5 minutes in the morning just before everyone wakes up, but it's been unplugged. There's no other sources that draw from the heater.

It's tough to assess the temp of the heater skin when exposed since it's basically a huge heatsink. Touching it really won't say much since there's insulation behind it. It's definitely not warm. I haven't measured it with a thermoprobe to actually come up with any quantitative conclusion. If I briefly stick my hand in between the blanket and the heater skin, it is somewhat warmer inside, so it's working to that effect.

Nothing special about the heater itself. It's just a standard natural gas fired burner with a bizzillion BTU/hr rating :-)

My guess is that the intrinsic heat loss is what it is and comprises the majority of the 'annual operating cost' sticker value that's stuck on the front. That's just the way stuff works.

If I ultimately swap out that 75 gallon tank one of these days, I'm sure a 40 or 50 gallon tank is inherently more efficient since there is less surface area assuming all else are equal and ignoring volume. We really don't need 75 gallons.. .it's way overkill

OTOH, a tankless heater sounds more and more interesting though. But I don't want to get that discussion started :-)
 
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Old 01-07-04, 12:40 PM
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alung-

Hey "neighbor" (I'm in San Jose, too). Yeah, that 75 gallon water heater is way more than you need. We've had a 50 gallon tank for several years and got two daughters through their teens without having any lack of hot water. My water heater is in the garage, too and I don't even have a "blanket" on it. The recirc pump is probably overkill, too. I find it's just as esy to turn the shower on before I brush my teeth. By the time I step in the shower, it's perfect.
 
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Old 01-07-04, 05:24 PM
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Hi: A. Lung

Assuming there are no problems with the normal operation or functions of the current water heater, downsizing the tank to a 50 gallon would be reasonable. Any size smaller is risky.

Any water heaters actual tanks available hot water output supply is about half it's capacity. Simply because it takes incoming cold water to push out the hot water. Minor factors aside, like dip tubes etc, 50-60% hot water is all there is available.

50 gallons suites the needs of most homes with 4 bedrooms and about 2000 2500 square feet. Water recovery times need to be considered and vary based upon incoming water temps, load demands and other factors.

50 gallons is the smallest size I would recommend to replace the current 75 gallon unit. Any smaller a unit would be self defeating. The current 75 gallon tank may be of it's size for unforeseen reasons, not just simple overkill.

The thermostat dials white marked area is the energy suggested conservation setting. In that setting, the faucet water temp should be in the 120 degree range.

The output water temp can be tested using a thermometer at any nearby faucet after allowing the water to run until hot. Mixer valves or single lever faucets should not be used for testing.

Some mix it valves and or single lever faucet often provide in accurate temp readings. Some valves simply leak cold into hot water, providing warm water. Experience teaches many things..

Before buying a tankless unit, when the time comes, read the post near the top of this forums list of topics. Also read some independant product testing magazines and consumers digest magazines.

Knowing what you are buying, whom in the area is the dealer and who fixes them after the sale when the time arrives, is worth the reading and knowing, before the purchase is made, in my opinion.
 
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Old 01-07-04, 06:31 PM
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Quote: We have a recirc pump--which to me is a dumb idea. If anything I have it on a timer for about 5 minutes in the morning just before everyone wakes up, but it's been unplugged. There's no other sources that draw from the heater.


hmmmm...I think this may be a spot you could adjust. When you were kicking it on 5 minutes before needed, you are dumping all the cold water sitting in the house (recircs are plumbed to the longest run) from all night into the tank. If the tank was near temp to need recovering that started the burner and you have a whole bunch of colder water in the tank for use just as you really need it. Id have it come on maybe an hour before you get up. The water would be hot all through the system. I'd rather spend a few more pennies and be comfotable myself. . Most of us don't have the luxury of optional instant hot water.

btw, I'd like to have that pump if you aren't gonna use it!
 
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Old 01-09-04, 11:53 PM
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The recirc pump return line is fed right into the drain outlet at the bottom of the tank, so, supposedly, all the cold water from the house is fed in about where the inlet feed is. There's a check valve that supposedly prevents the cold water from flowing back into the hot water line when someone turns on the tap in the house (although I wonder if it isn't jambed open since sometimes I'll run the hot water for several minutes and it'll still be cold) There's a valve on both sides of the recirc pump, so I can shut the whole thing down.

Instant hot water isn't always the case unless the recirc pump is running all the time. All that hot water running through the house ultimately cools off fairly quickly once the pump turns off. :-(
Otherwise all it does is heat the attic and/or crawlspace ;-)

Interesting observation after I put that foil lined blanket. For kicks and grins, I put the original R-10 fiberglass blanket over the R-19 foil one (since it's thin). Technically, I now have about the equivalent of R-29 over the heater. Guess what... it's still warm under the fiberglass blanket!

about the heater gallonage sizing-- the relationship between house square footage and water heater size never really made a whole lot of sense to me..I'd think it would be more of a function of how many people would ever use all the dish/clothes washers, and filling all bathtubs simultaneously. But that seems unlikely for the same reason there are multiple AC outlets strung on a single circuit breaker

[rant] new houses these days seem to have more bathrooms than bedrooms which is downright stupid! I guess some feel it's a sign of luxury? sheesh...
 
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Old 01-10-04, 12:06 AM
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Just one more thing about recirculating pumps. Sometimes they can get an airlock that can be very stubborn. Could be yours is doing this since it's getting stopped and started all the time. I'll leave it alone now...good luck!
 
 

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