Standard 40 gas HWH VS. a wall hung ??

jp_2

when you think about it, you have a 3" tube running through a 16" tube filled with water. your delta T is not that large, about 60F air to water temp. you are relying on convection air current to cool the tank, you are not going to get big air currents in this little tube. biggest losses come from inefficient transfer of heat during firing.

electric water heater seem to loose about .75F per hour. not that different from 1F per hour.

ScottMP

Last night at our

Plumbing meeting we were discussing HWH and one of the members said he had been at a discussion where some numbers where discussed.

Now this came from the VP of a MAJOR water heater maker here in the U.S.. The comments where that the claims of a wall hung unit saving money from stand by loss was un founded. The numbers stated where that a 40 gallon gas HWH simply maintaining temperature using a standing pilot would use about .15 cents a day ( give or take your area ).

My thoughts where that it sounded low and that the chimney effect of a standard tank would cool a tank off much quicker. This brought up the comment that a stadard tank losses a degree an hour in standby loss. Givin that most indirects will claim less than 1/2 a degree an hour, this also sounded a bit optomistic to me.

I thought about it and said to myself " Scott, where would you go to really get the real truth ? Who would have the knowledge about the products with no slant towards sales ? "

So ..... I'd love some information here guys !!

Scott

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ScottMP

Anyone

else ????

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Unknown

personal tests

Scott,

Turn off a gas water heater and go on a two week holiday, you return to a tank of cold water.

Turn off the switch on a indirect water heater (and the boiler that is heating it up) and go on the same holiday.... come home and flick the switch, everything is still hot enough that the boiler does not even call and everyone gets hot showers.

Personal experience.

steve

jp_2

WOW!!!!!!!!!!

so, you are suggesting an indirect only loose about 1degree per day ?

STEVE PAUL_3

THREE INCH TUBE

That 3" tube in the water heater is actually around 3.5 square feet of surface area. That is a substantial heat absorbing/ transfer plate.

jp_2

need to

measure draft, then you have a delta T and velocity so you can calculate actual loses up that little stack.

it can't be that great of a transfer surface, I've measure over 350F stack temps during firing, plus I've measured efficiency at 70%, not too good heat transfer.- 30 gal 29,000 btu unit.

ScottMP

Interesting

So no one knows the excact amount of the stand by loss of a standard tank ??

Tought to sell the benefits of a wall unit when you don't have the facts.

Scott

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Unknown

in my own basement

I know, I know, all I didi was a simple little switrch test with absolutely no measuring devices except the roar of fire on the water heater.

I think a lot of lose on the indirect are through the stand. I think a lot depends on how warm/cold and what mass concrete/plywood you have below it. IN my own application the tank was directly on a concrete floor that was 8 feeet below grade, The floor never got below 60F.

So yes, about a degree a day on the indirect.

I have been told, without formal tests that a standard gas water heater will lose 3 degrees and hour. Of course this was before the upgraded federal mandate of better insulation and different air inlets that took place three years ago.

Steve

Mike T., Swampeast MO

Supposedly [some] manufacturers give a standby loss rating for their stand-alone water heater tanks. In the absence of such you can calculate standby loss using this equation.

(Note that it's a multiplication symbol to the right of 67.5 in the denominator.