HX on shower drain.

Alan (California Radiant) Forbes

It's a lot of trouble to save a few pennies.

unclejohn

Grandma always said if you watch your pennys the dollars will take care of them slelfs.

Leon82

It's good for a tankless heater to warm up the incoming water temp

hot_rod

An energy lab in Canada that tests all sorts of "devices' from solar to Hps, windows, insulation etc claims the bang for the bucks is actually pretty good. I think ME did some looking into the viability also.
Be nice to get the dishwasher running in also, seems it's all hot discharge, especially when the temperature boost cycle is used.

Mith

Astoundingly, studies in passive homes have actually showed up to 60% recovery of the DHW energy inputs from these. Even at the lower bound of real-world studies, depends how much DHW you make - 10% ain't nothing and all the studies seem to show at least that. Think of a DHW production system serving a laundromat or the laundry room for even a small building of apartments; this is a slam dunk.

That said the manufacturers of these systems typically advise against using them in applications without separate grey water drainage. I think they want to avoid liability for fecal bacteria contamination of the cold water side though this seems extremely unlikely to occur given the multiple layers of copper involved. If I could find one in 4" or 6" that was in fact rated for use on arbitrary waste lines, I'd buy it in a minute; I've got setups like drains that serve huge laundry rooms plus one or two office toilets, one line of apartments, etc. where there would definitely be a lot of energy recovered.

hot_rod

The Canadians seem to be the leaders in the technology and use. Some of the utilities include them as part of their energy conservation program. Good ROI when they are free

Mith

I actually just looked at one of our buildings and realized that by moving a single toilet waste drain, I could use this type of unit on the grey water coming from 26 very busy washers.

Now I'm wondering how best to do it. This system has a (very large) condensing DHW heater (condensing boiler with plate heat exchanger) feeding a long recirculating DHW loop through a temperature control valve. I don't really want to raise the temperature of the input to the heater; I think I should have the magic heat recovery drain unit plumbed into the cold water feed to the mixer. Whatever the output temp of the recovery unit, it will be below my mixed DHW target, so this seems unlikely to cause any problem - and it will avoid losing efficiency at the heater by not condensing as much. Does this seem right?

Only concern would be destabilizing the PID in the mixer, but, this is a Heat-Timer ETV and they're pretty robust about that.

Jamie Hall

Grey water's fine. But on something with grease in it... after the grease trap, OK. But before? What a mess...

Canucker

@Jamie Hall The risers I've opened never seem to have a lot of grease on them but they tend to at least be around room temperature most of the time. Our incoming water is sub 40F in the winter and I wonder how much more would catch on the sides at a much lower temperature?

kcopp

I have one in my home. Master bath shower feeds the whole house water heater. Been in 14 years now. Takes the edge off the incoming water.

Alan (California Radiant) Forbes

Maybe for commercial use, but for a single-family residence I don't get it. Twenty-five bucks a month for DHW and you're going to save how much with this device that's going to save maybe, just maybe $1 every month. Why bother?

Oh yeah, something to show my friends and relatives to show how smart I am about conserving energy? You know, I've got better things to do..........please.

Solid_Fuel_Man

It cost more than $25 a month to heat water here in the NE.

Check out some data on these. I actually piped my place for one (nice long vert run of gray water only). Never bought or built one. I've heard they save about 30% on DHW.

Surprised California hasn't made them code too! Lol

hot_rod

Alan (California Radiant) Forbes said:

Maybe for commercial use, but for a single-family residence I don't get it. Twenty-five bucks a month for DHW and you're going to save how much with this device that's going to save maybe, just maybe $1 every month. Why bother?

Oh yeah, something to show my friends and relatives to show how smart I am about conserving energy? You know, I've got better things to do..........please.

I think the key differences between CA and "back east" is incoming water temperature. Milwaukee city water runs around 34F during much of the winter.
My well hovers around 52F all the time.

Phoenix city water rarely drops below 80 year around.

You mileage may vary.

SuperJ

There is good science and studies showing drain heat recovery is well worth the couple hundred dollars it costs. Especially here in Canada with our cold entering temps. In the grand scale of all the fancy gizmos that go into modern hydronic system, DWHR is a no brainer up here. It makes even more sense when you're dealing with an instantaneous DHW heater.

I agree the cost to heat your DHW is low compared to heating your house (at least on NG) so it's easy to ignore.

GroundUp

I built one of these last year in a similar fashion to a sidearm heat exchanger, with a 1-1/2" Type M copper core inside a 2" Type L case with 3/4" tees at each end. I didn't have the space for a vertical installation, so I built it 8 feet long and placed it in a horizontal position just before the exit to my septic. I disconnected my 2 showers, dishwasher, and laundry drain from the main sewer and routed a new "gray water only" line through this HX. I haven't done a ton of testing, but the results from my original test is that it will pull almost exactly half of the heat out of my gray water and send it back to the cold side of the water heater. My shower temp is 114 degrees- when it reaches the HX, the grey water is 111 degrees. My groundwater temp is a consistent 47 degrees. During a shower, the incoming water temp to my WH tank is 77 degrees while the discharge to the septic is 79 degrees. Using that data, my calculations say that is 22,000 BTU per day with the 2.5 GPM head and 35 minutes of total daily shower time. Considering the efficiency of an atmospheric LP water heater, we're talking 1/3 of a gallon of LP per day saved with this stupid thing on showers alone. No, it's not a lot, but added up over a year to include laundry and dishes as well, we're talking 180 gallons a year. LP has been running about $1.25 the past few years- you do the math. I built this before I realized others had already done it, it was kind of a wet dream, but it actually worked out pretty well. I'll get my money back in a year, and save a couple hundred every year forever.

Alan (California Radiant) Forbes

Nice!

Knowing me, I'd probably take longer showers knowing that I was saving all that money.

Solid_Fuel_Man

I love long showers....its where I do all my thinking.

hot_rod

solar dhw in my answer for long showers. Let the sun do the heavy lift.

mikeg2015

We are talking a 2 gpm shower for 30 minutes per day. Drain temp of 95f. So let’s say you recover 15f. You’ve gotten back only 1/4 of the energy. That’s around 2 therms. Or $2 per month. Woohoo. That what my boiler uses each hue it’s running in winter.

But if you have a tankless water heater or heat pump WH, you lose 2-3% economy from Higher entering water temps.

Larry Weingarten

Hi, I got one of these back when GFX was making them. The claim (from measured data) was it captured 60% of the "waste" heat. I piped mine directly to the cold side of the shower as the run is only 4-5 feet, eliminating the losses involved in running a much longer line back to the water heater. In 2006 a five foot unit was about $350.
Now for some assumptions. If about half of our hot water use is in showering and if the drain heat exchanger recovers half of the energy, that suggests a 25% reduction in hot water use for the life of the house. Also it could mean that when you go to replace your water heater, it could be downsized.

Yours, Larry