Grunfos Domestic Hot Water Recirculation System
AKA. “Instant Hot Water”-Pros and Cons Please
Comments
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Pro: Hot water gets to your taps more quickly while the recirc pump is running
Cons: Higher energy bills (your water heater will need to run more to keep that recirc line hot), either need to install a dedicated recirc line or connect the hot and cold lines at one or more fixtures.
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I have almost instant hot water at the faucets by a system I installed myself using a dedicated line from each of my 3 bathrooms. I installed the smallest B&G bronze pump (38 watts) that I could find at that time and added a cheap plug in timer so I did not have to have a licensed electrician to do any wiring. It has been working trouble free for about 27 years. Do I worry about a few $ of cost expenses or savings? My answer is simple as you married guys will agree; my wife is very pleased, so that makes me a happy guy.
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Which model? Grundfos has a few to choose from.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
I have a gravity recirculation system for DHW. 24/7/365 for over 10 years.
No pump, no tstat, no electricity used. Just a flow control and check valve at the bottom of the tank. Insulated supply and return lines.
Yes, it is another heating circuit that constantly provides some heat in a house that has some hydronic heat running for about half the year anyway.
I have mentioned this before and have gotten some small stones thrown at me for wasted energy.
But as Retiredguy points out, perhaps some additional NG costs. If I was really green I would try to talk my wife into no hot water use needed……..and I would be living alone here.
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Hi, If you go with recirc, look at "demand controlled" systems. They will only activate the pump when you want, so use at least 90% less energy. If you have the option, I like to use manifold systems in "not too big" homes. They have less to go wrong. and can save water and energy. With 60 psi supply pressure I've been able to use 1/4" tubing for the runs 😉
Yours, Larry
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Me too…
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Will gravity push open the check valve in that thermostatic cross fitting ?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
yes, it works well for 2nd floor fixtures ( 16’ vertical and 20’ horizontal, 1/2” supply). Wife’s sink has warm water in few seconds and hot in about 15 seconds. Same for the shower. Without the grunfoss valve, the low flow sinks would take 2 minutes and shower about 50-60 seconds. Kitchen sink is on same branch so it gets hots water faster as well.
Bit more NG usage Is a good trade off to increase spouse’s comfort and reduce water use.
As a test, I installed same setup on a 1st level bathroom with 6’ vertical and 60’ of horizontal 1/2” lines from the tank to the sink. Not effective, too much friction in the horizontals for the small delta in elevation to overcome.
PS: the slight delay getting warm water to Wife’s sink in second floor bath is due to the grunfoss valve being installed under my sink a few feet away. Planned on installing under her sink but let’s just say her cabinet utilization is much higher than mine so I chose the easier path. 😂0 -
The only complaint I've had is that the thermostatic valve in the crossover fitting closes at 100℉. Warm, but not hot.
And I don't know what the differential is.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
that’s the ideal temp for face washing per my better half!
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I damaged the threads on this valve so I cut it open to see the insides.
It is basically the same as a thermostatic mix valve. thermal motor a few springs. It has a tiny check, about 1/4" diameter and a small screen protecting it. I imagine those are the fail points from scale or dirt accumulation.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Love the easy to read Caleffi pencil artfully posed in picture as contrast to obscure Grunfoss label. 🤣
The valve in the picture was installed in 2014 and going strong. Imagine it has a lot to do with our good water quality as you mentioned.
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We get nearly instant hot water with our pumpless gravity system
About 10' vertical and 65' horizontal of a mix of 3/8 and 1/2 ID copper. (Clean out the shop.) We were able to get slope for most of the horizontal run with a drastic drop at the WH. The drop at the WH is purposely not insulated as a cooling leg to promote gravity flow.
Another advantage is we get circulation thru the 120 gallon WH tank, (Rheem Sundirector, clearance at a wholesaler, 1994) keeping all the water closer to the same temp.
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