Feeding hot water to the cold side of an electric WH

[Seasoned Oak]

I was wondering if there is any downside to feeding hot water into the cold side of an electric WH. My boiler produces water that is much hotter than my electric WHs normal setting. So the water will be entering the heater on the cold side very hot at times ,as much as 160 Deg(Est) I use the electric whenever i shut down the boiler which is in all mild weather and in both shoulder seasons. I never shut off my electric as they dont last long siitting with cold water in them ,tend to rust out in no time. The electric would actually run less overall as the water coming in is hotter than the setting.

 

[maple1]

Assuming of course there is an HX in between?

My electric water heater sees pretty hot water coming in when it is heating. I have temp probes at the element locations, I have seen over 160 sometimes - I don't run my boiler temps as hot as I used to, so that is about the max it gets.. The only 'bad' thing I have noticed is that it will trip the overheat breaker on the top element - have to reset it when I want to go back to electric. My heater is a bottom fed though, and the hot comes in the top, not sure that matters. I have the control probe for the recirc pump at the bottom fitting, and it isn't set that overly high. But my recirc pump circulates pretty slow, so I get big stratification inside. If I were to turn the flow up, I likely wouldn't see it get so hot at the top.

 

[Seasoned Oak]

Im pretty sure the cold side has a tube that delivers the incoming water to the bottom of the heater ,so it should mix with the rest before it gets to the top element. ID have to bypass my boiler whenever its not in use as i dont want cold incoming water going thru an inactive boiler as it will sweat and cause a lot of rust.

 

[maple1]

Ok, I guess you have a coil in your boiler?

I'm not so sure that letting it run through your boiler in the summer would cause any condensation. If your boiler is cold (assuming it's shut off?), there would only be maybe a 20 degree temp difference between incoming cold, and what's in the boiler (depends on the situation). And I know when I had my wood/oil unit with coils in it, I sometimes needed to have flow of boiler water through or around inside the boiler to get much heat transfer between the boiler water & water in the coils (they needed to be 'washed' by the boiler water, or else my DHW wasn't hot enough, at anything below 140f boiler temp). So I don't think the water in the boiler, would get cooled enough to make the boiler sweat. You very likely would get some condensation on the pipes going in & coming out though.

 

[Pat32rf]

Any time your domestic hot water gets much above 140F you are setting yourself up for big trouble when a guest or child gets scalded. When I was servicing hotel and apartment electric water heaters it was worth my job if I left the controls set above 140F. It only takes a few seconds under a tap that puts out 160F before you start loosing skin and flesh.

 

[maple1]

Yes - that's why you also put a mixing valve outside the tank outlet.

 

[STIHLY DAN]

Hot water entering the cold inlet will have no issues. You will need a mixing valve though.

 

[Seasoned Oak]

Hot water entering the cold inlet will have no issues. You will need a mixing valve though.

Thats what im trying to eliminate, the mixing valve. Mine was very expensive , and every time i turn around its leaking. PITA

 

[Seasoned Oak]

I made the switch and i did have issues . So far iv had 2 leaks ,which i believe are mainly because the water pressure is going up high due to the very hot water coming into the heater, and no expansion capabilities like the heating side of the coil has. I now have the Electric WH breaker switched off completely and the water is still too hot. Iv reduced my boiler temp which should help some. Im now essentially using the Turned off electric WH as a holding tank. For now going into milder weather i can live with cooler water feeding my HW baseboard.

 

[maple1]

I don't think I have a clear pic of your setup, I think I missed something.

If its a tankless coil, then hot water being too hot should be less of an issue now that it is being mixed with holding tank water, than it was if it was going from coil to taps before.

 

[Ncountry]

If you have a domestic hot water coil in boiler it seems like it would be fairly easy to install Ts in the cold and hot line on hot water heater and run a circulator pump controlled by an aquastat on hw heater to control temps.

 

[Seasoned Oak]

Im going for as simple a setup as possible. Iv had mixing valves for years and they are expensive,problematic and leaky. One quick fix would be to put a tee in the cold supply side and feed a small amount of cold water into the hot side to bring the extremely hot water down to manageable levels. What i use to refer to as a "poor mans mixing valve" . Right now i have 180 degree water feeding into the cold side of a 30 gallon electric water heater. Most of the time the water is too hot as even though the water heater breaker is turned off the water does not cool down fast enough to domestic use temps. With 6 people in the house it gets a constant supply of very hot water.

 

[Seasoned Oak]

I don't think I have a clear pic of your setup, I think I missed something.

If its a tankless coil, then hot water being too hot should be less of an issue now that it is being mixed with holding tank water, than it was if it was going from coil to taps before.

It went through a mixing valve before , but im trying to do away with the mixing valve for reasons stated above. The holding tank water does temper the water ,but it depends how much its used as the more hot water you use the hotter it gets.

 

[maple1]

When I had my tankless coils (2 of them, in series), the temp of the water coming out would decrease with extended usage. My boiler didn't spend a lot of time in the 180 range though. Thinking the partial bypass might be the easiest way to go for you, if your tank is getting too hot.

 

[jdstigall]

Well, if your water heater malfunctions then it will allow the water to get too hot.The extremely hot water may be due to thermostat malfunction. This was the problem with my 20-year-old water heater when we were in NJ, and on inspection, we found it to be replaced and got the new water heater installations NJ.

 

[Seasoned Oak]

When I had my tankless coils (2 of them, in series), the temp of the water coming out would decrease with extended usage. My boiler didn't spend a lot of time in the 180 range though. Thinking the partial bypass might be the easiest way to go for you, if your tank is getting too hot.

I did just that ,i cracked the valve a little coming in from the all cold water line and it immediately brought the overall temps down to a manageable range.
I think i got the right formula now. Water is not in the scalding range anymore.

 

[Seasoned Oak]

Well, if your water heater malfunctions then it will allow the water to get too hot. .

My water heater breaker is switched OFF . No way for it to malfunction. Im essentially using my electric Water Heater for a holding tank to temper 180 degree hot boiler water for domestic use without using any electricity. This setup also allows me to turn the power to the WH off and not damage it with corrosion that usually occurs when the appliance sits with cold water in it for long periods of time during winter when my boiler heats my hot water. I usually never shut off my electric WH ,even when its unused for months over the winter ,as they rusts out really fast when i did that in the past.

 

[Pat32rf]

One solution that I used to use was to connect a ball valve handle to a 24v damper motor. The motor was controlled by a stat on the discharge line so it controlled the blend of hot and cold.....more cold when the temp went above 130F.
Even worked on a 100kw 600V water heater in an old apartment building..

 

[velvetfoot]

My water heater breaker is switched OFF . No way for it to malfunction. Im essentially using my electric Water Heater for a holding tank to temper 180 degree hot boiler water for domestic use without using any electricity. This setup also allows me to turn the power to the WH off and not damage it with corrosion that usually occurs when the appliance sits with cold water in it for long periods of time during winter when my boiler heats my hot water. I usually never shut off my electric WH ,even when its unused for months over the winter ,as they rusts out really fast when i did that in the past.

I usually drain my electric water heater in the winter. Is that better, as far a rust goes?

 

[Seasoned Oak]

I usually drain my electric water heater in the winter. Is that better, as far a rust goes?

Not sure if thats better,i felt that it would still be wet inside and cause rust as rust need air to form,i feel im better off using it as a holding tank which increases my supply of hot water to almost unlimited, and also prevents rust by keeping everything hot and dry.

 

[Pat32rf]

Never thought of draining an electric tank, just keep it warm, or better yet hot. Use it for storage....

 

[Seasoned Oak]

Never thought of draining an electric tank, just keep it warm, or better yet hot. Use it for storage....

These tanks tend to have tiny leaks,which can cause rust on a cold tank ,keeping it hot lets any moisture evaporate before it can cause damage. Iv had a brand new water heater rust out in less than a year by letting it stand with cold water in it. My current electric WH about 6 years old now.