Hot water circulation pump - Talk me into or out of it.

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Old 01-14-21, 08:13 AM
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Hot water circulation pump - Talk me into or out of it.

I've been on the fence about adding a hot water circulation pump for years. Especially now with all my home automation stuff I could easily turn the pump on when someone enters the bathroom.

Cold water return or comfort valve type. I could fairly easily run a return line from the furthest fixture back to the water heater vs installing a valve under the sink.

But where I'm torn is I read you need to remove the heat traps from the heater, and even without the pump running you get convection circulating water thru the pipes and thus heat loss.

Does that heat loss outweigh the convenience of having hot water right away at the tap?
 
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Old 01-14-21, 10:41 AM
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No, you do not have to remove the heat traps from the water heater in order to have a recirculation loop.

Heat traps are vaguely like check valves. During recirculation water flows in the same direction as normal flow so the heat traps do not affect the pumped flow.
 
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Old 01-14-21, 11:43 AM
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Interesting. I'm not sure where I read about getting rid of them for the recirc pump to work. Possibly in some amazon reviews. Looking at the installation manual for a couple pumps I see nothing about it.

So I don't really see any other cons for a recirc system, besides the cost and installation time.
 
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Old 01-14-21, 12:27 PM
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I see two benefits to recirculating hot water. You get hot water at the faucet much faster and you are not wasting water by letting the tap run until the hot water gets there.

On the down side with a circulation system you are turning your water piping into a radiator that is on all the time. Some of that heat is lost/wasted outside, not good in winter. In the summer when you are running the air conditioning to cool the house those hot water pipes are also radiating heat into the house that you have to air condition out so you pay for it twice, heating and cooling. Then there is the energy consumption of the pump and one more mechanical thing in the house that can break.

As far as the heat loss that depends on your house. In a new construction I would insulate all the pipes to minimize the loss. In an older house much of the piping is probably not accessible so you've got bare pipes loosing heat. Heat loss is partially determined by the difference in temperature between the water and the room. 120f water running through a bare copper pipe in a 40f crawl space can loose a lot of heat.

The chart below shows approx. how much heat a uninsulated copper pipe looses. Each colored line represents the difference in temperature between the water in the pipe and the outside air. The bigger the difference the faster heat is lost. So, each foot of bare copper pipe carrying 120f water running through a 40f crawl space will loose about 40 btu per hour. A ten foot section of pipe would loose about 400 btu/hour...

 
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Old 01-14-21, 12:46 PM
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I was under the impression that the heat traps were installed to keep the hot water from naturally flowing (thermosyphoning) out of the water heater which in this case is exactly what you want to happen.
 
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Old 01-15-21, 07:33 AM
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Thanks for the replies guys.

Pilot Dane,
It is an older house, but I actually can fairly easily insulate the hot pipes in the basement. Actually they already are for the most part.

As for all the time, I'll use a smart outlet to cycle it on as needed. I imagine it would run for under an hour or two a day total.

PJmax,
That has been my understanding too. If they'll work fine with a pump, then great. But if you would some reason need to remove them you could end up with that syphoning effect without even having the pump running. (Definitely don't want that)
 
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Old 01-16-21, 05:53 AM
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The purpose of heat traps is to prevent thermally induced eddy currents from carrying hot water up and out either or both of the hot outlet and cold inlet and then come back down the same pipe, cooled off so as to need reheating, all 24/7.

Certain kinds of twists and turns in the pipes above the water heater will limit the length of travel of eddy currents and therefore reduce heat loss.

A recirculation loop may or may not have a gravity induced (thermally induced) flow all the way around the loop when the pump is not running. Sometimes the loop has only a gravity flow with no pump.

I was unable to remove the old anode rod for replacement. So I ended up getting a nipple style replacement anode that goes into the hot outlet port. I had to take away the heat trap nipple and will have to think about trapping eddy currents at a later date.
 
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Old 01-16-21, 10:13 AM
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I was under the impression that the heat traps were installed to keep the hot water from naturally flowing (thermosyphoning) out of the water heater which in this case is exactly what you want to happen.
Heat trap nipples do not impede flow, just the transfer of heat without flow.
 
 

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