DHW Tank Heat Loss

Seems like a lot, but I've never measured the loss on mine...

I find that the water tank temp drop depends mostly on outside temp. I get my Tarm up to 180+ for overnight by 9 pm, if it is real cold overnight, say 20 below with wind, it might be in the 140s in the morning. This time of year I usually have temp around 165 at 6 am. I have a temp gauge near the kitchen to keep track. we keep the house at 68 (or higher when requested).

What do you have for a tank? That seems like a lot of standby loss. I have temp guages on mine, at the element locations. I haven't really watched them close for standby losses, but I think if I heat my tank up that hot it will go for 2-3 days before it needs heated again.

huffdawg said:

This is a graph showing the temp drop in my DHW tank over approx. 13.5 hrs. from 7pm to 8:30am
Looks like it dropped from 160f to 125 in that time.
The bar graph along the bottom shows related circ. pump operation duration.
Does this temp drop seem like a lot for a dhw tank that is stacic for that amount of time?
Anybody else monitor their dhw tank?

Huff



View attachment 177631

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That seems really high to me. I have a 50 gallon Indirect Hot Water Heater and I would say that I lose well under 10 degrees in that time frame. I don't actually measure it but I still have my DHW tied to my propane boiler and I can see on a graph when the propane kicks in, this only happens when there is a big call for DHW (lots of laundry, showers, Dishwasher, etc.) - I have never seen it kick in overnight with no big use of DHW.

Doing a little "improvement" rework recently, I have the insulation off some pipe. I noticed a heat flow around the buffer tank. I believe it was due to a convection loop. I put in a check valve and it seems to have helped. I never noticed before because the pipe insulation is an inch. Now, you may ask, "if you don't notice the heat loss, why do it?" That's why the quotes in "improvement".

Not surprised by this heat loss. Based on a separate DHW meter, our household electricity use for DHW dropped by 50% after I super-insulated the two tanks (100 gal total), raised them off the floor and insulated underneath, added U-shaped heat traps, and insulated all the exposed hot water pipes.

In my house it's only a loss in the summer. In the winter it's just helping to heat the house.

jebatty said:

Not surprised by this heat loss. Based on a separate DHW meter, our household electricity use for DHW dropped by 50% after I super-insulated the two tanks (100 gal total), raised them off the floor and insulated underneath, added U-shaped heat traps, and insulated all the exposed hot water pipes.

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I did most of that too. 80 gallon electric. It's on a stand I made out of 2x4's, with a layer of foamboard underneath. I put in heat traps after the fact, and wrapped it in 4" fiberglass under a layer of bubble wrap to keep it in place (that job turned out more tedious that I thought it would be - tight space & not enough hands).

Before I did it, I thought it would be a waste of time since I never really felt any warmth on the tank surface. But since doing it, I can lift up the top layer of insulation, and definitely feel a warm tank top underneath.

Which was also why I was asking exactly what was there for a tank - likely any tank you can buy has room for improvement with a few DIY add ons.

160 degree domestic hot water!
I helped a couple of local farmers butcher some pigs last week and one of the first steps was pouring 153 degree water over them. After that the outer skin and hair peeled right off. Amazing to see, but very scary when I hear about people with 160 degree water available in their shower. Just bump the tap or diverter valve and its hospital time...with someone else driving!

He didn't say it was 160 at the taps - that's what mixing valves are for.

A short down then up, on the ins & outs of the tank on top.

I soldered some in a year or two ago. Think the down is about a foot long. Stops (or should) heat convecting up the pipes and out of the tank, the heat won't sink into the low spot so stops when it gets to the downturn.

My electric tank also came with what they called heat traps - little plastic 'somethings' on the inlets/outlets. Not sure how good they were working. So now I'm double heat-trapped, I guess.