DWH recovery rate question

Tom Towne

Hello Guys

I have some questions about my Bradford & White water heaters performance. I use it as a constantly circulating radiant system with 800ft of 7/8 PEX. The water heater is a 50 gal, 65,000 BTU with 80%recovery rate and 3 months old. Flame looks good

My question is this. How can it take 25-30 minutes for this unit to heat the returning water from 118deg F. up to the 145deg F. shut off point. Seems as a 20 deg rise should not take this long. I am just trying to figure out if the unit is working properly. Thanks.

jp_2

tom, I looked at the same thing with my gypcrete installation with constant circ.
1/2hr to reheat water heater-30 gal, 26Kbtu. so, if i turn circ OFF, tank heats in 10-12minutes.
you are heating up the tank, all water in floor, like 20 some gallons plus all the plywood. (i guessed at 20 gal.)
try it. I use this to figure actual heat loss.

jim

kevin coppinger_4

if I am not mistaken...

800' of 3/4" pipe is about 200 gal. of water...thats a lot of water...kpc

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GW

depends

on several variables. the most obvious one is how much BTU the radiant is delivering.

without knowing the gpm of the radiant system, you won't really know how much the system is demanding. (gpm x delta t x 500 = BTU)

I'm a bit out of the loop when it comes to water heaters, but 80% seems pretty high. If you really wanted to split hairs, you could calulate the therms or cubic feet of gas needed to heat the floor- yes there would be some math involved. I bet 50 cents your not getting anywhere near 80% of true efficiency.

Gary



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hr

What's the load on the system?

The building is using the heat the water heater is producing, if I read your post right, and the circ is running. The delta T will be dictated by the system (building) load.

hot rod

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jp_2

if you turn the pump off, does it take about 12 minutes?