Waste Water Heat Recovery Pipe

JakeCK

How many of you have experience with these and what are your opinions? I searched the forums and the posts I found were mostly from 15 years ago. I would think it would prove especially useful for indirect hot water tanks? 

The orange bigbox store sells the power pipe. The original GFX brand one doesn't seem to be available anymore. Atleast that I could find.

Larry Weingarten

Hi, I installed a GFX years ago. It’s buried in a wall, so I can’t measure just how much it’s doing, but can say that when using that shower, I do need to throttle back the hot water after about ten seconds, as it heats up from having warmer incoming cold water. No maintenance and a claimed (by testing) 60% reduction In hot water use seems good to me.

GFX is no longer made that I know of. In Canada, these are pretty widely accepted.

Yours, Larry

Jamie Hall

I have no direct experience with any particular brand, but I am familiar with the concept. They are, of course, simply heat exchangers with the waste water on one side and the water supply on the other.

Perhaps the plumbing codes have changed, but decades ago -- when I was enforcing them -- such an arrangement would have been flatly prohibited.

JakeCK

Jamie Hall said:

I have no direct experience with any particular brand, but I am familiar with the concept. They are, of course, simply heat exchangers with the waste water on one side and the water supply on the other. Perhaps the plumbing codes have changed, but decades ago -- when I was enforcing them -- such an arrangement would have been flatly prohibited.

Which code would have them prohibited? Asking because I'm genuinely interested, not to be a smartass.

The only thing I could find when I did some light research a while back was something about double wall construction.

Jamie Hall

The old National Plumbing Code (I told you it was a while back) prohibited any pipe arrangement where water pipes were in contact with, or inside, any waste water pipe. I forget now -- it's been years -- which section it was, but it was in the same part of the code which mandated reduced pressure zone backflow preventers or air gaps on any fixture which had both a domestic water supply and any other water (such as waste water -- or a boiler).

Double wall construction, with a positive and completely unobstructed path to drain from the space between the two flows would alleviate the concern. It would also, I think, reduce the heat transfer to pretty close to nil.

JakeCK

I did some more digging on the codes. It appears to be explicitly allowed, at least as of the 2019 Ohio Residential Code.

N1103.5.4 Drain Water Heat Recovery Units

https://up.codes/viewer/ohio/irc-2018/chapter/11/re-energy-efficiency#11

JakeCK

Youngplumber said:

Also no experience with this. But it seems like one of those good ideas in theory but in practicality not the easiest to get a lot of benifit from. Maybe coupled worth solar water heating.

Just my two cents which aren't worth much. Lol

The reason I'm interested in this is because our water gets REAL cold in the winter courtesy of the above ground castle looking reservoir across the street from me. And when I say cold I mean nearly ice cold. Heating that up to even 50 or 60 degrees would be a massive gain.

kcopp

I have one in my home. It works ok.

JakeCK

Cost. $850 for a 4" 48" long pipe that I can install my self is much lower barrier to entry than a full scale solar setup. And supposedly these things are capable lf recovering up to %50 of the wasted heat. I'm just curious if anyone has any personal experience with hard data using them. Short of that anything else is speculation or guess work.

JakeCK

I'm half tempted to get one just to test it and get some data. Would be an interesting experiment. I could use the same sensors I'm using on the boiler to read supply and return temps. I used ds18b20 temperature sensors strapped to the supply and return copper right off the boiler. I get pretty accurate readings on the home automation. Something like that could easily track just how much I would get out of the heat exchanger during the course of a shower.

JakeCK

Youngplumber said:

Share your data. I'd be interested.
Start clocking btu usage now and then do it after you install with the same water usage. That would be great. 

Luckily, I've saved almost all of my gas and electric bills on my computer since I've owned this house. For the longest time I even had them graphed out in excell. Shouldn't be hard to figure out the difference during non heating months. Winter will take some time to gather new data. 

psb75

Seems like: you would have a 3" copper DWV pipe at a 4' length, surrounded by a pvc "jacket" pipe (4" dia.) that contained potable water. The pipe would be installed on a part of the DWV system that handled ONLY "gray-water" (which plumbing codes don't generally recognize--ALL waste water is "black"!), i.e. bath/shower, laundry, dishwasher discharge. The potable water jacket would have to thermo-siphon or be electrically circulated to the DHW storage tank in its own "loop." It would be good if the discharge of the warm waste-water could be retarded to improve heat exchange, by reducing its "pitch" or maybe even reducing its diameter to 2" copper. Just a thought.

Canucker

@psb75 There are drain recovery units that get installed horizontally. I think those would be a nightmare for service, based on my last look at them. The vertical units have your cold water piped through its jacket before it heads to the rest of the system. The heat in the waste flow is what it's targeting. I don't have one so I can't tell you any real world experience with them

Jamie Hall

On the code question -- fair enough. A lot of things have changed over the years!

JakeCK

psb75 said:

Seems like: you would have a 3" copper DWV pipe at a 4' length, surrounded by a pvc "jacket" pipe (4" dia.) that contained potable water. The pipe would be installed on a part of the DWV system that handled ONLY "gray-water" (which plumbing codes don't generally recognize--ALL waste water is "black"!), i.e. bath/shower, laundry, dishwasher discharge. The potable water jacket would have to thermo-siphon or be electrically circulated to the DHW storage tank in its own "loop." It would be good if the discharge of the warm waste-water could be retarded to improve heat exchange, by reducing its "pitch" or maybe even reducing its diameter to 2" copper. Just a thought.

Huh?

What your are proposing wouldn't meet code, and just sounds bad since it wouldn't even be double walled... 

All the commerical off the shelf solutions are just copper DWV pipe wrapped around the waste stack. They come in various lengths and diameters. It is doubled walled construction since the DWV is self contained copper and the potable water lines are also self contained copper tubing. The two are, I believe, soldered together for thermal transfer. They also use counter flow so the incoming cold water starts at the bottom with the coldest part of the stack and moves up towards to warmer top. The water pressure from the well pump or city water is used to move the water normally to the hot water tank and/or mixing valve for the fixture(s). It is that simple. No electrical, motors, pumps, valves, or any other moving parts to go bad or wear out.

Also there is a small manifold at each end where the 3/4" supply gets split up between multiple smaller dia. pipes. This increases surface area and if it increases overall volume would slow the flow while it is moving through the exchanger. 

GroundUp

I have no experience with the factory made variety, but for grins a couple years ago I had some leftover fittings on a job and built what is essentially a "sidearm" HX often used with wood boiler systems to heat the tank water via thermosiphon. It's 8 or 10 feet long, with a 2" Type L outer shell, 1-1/2" Type M inner tube, and 2"x1-1/2"x3/4" tees on each end with the stops filed off so the 1-1/2" can pass straight through. Given the length, it is installed horizontally and almost flat but it is held in with Fernco couplings if service is necessary. Also it is only piped to the drains from my showers which rejoins the main prior to exiting the house, so it doesn't help with anything but showers however that accounts for 95% of the hot water used in my house. I haven't checked lately so I don't remember the exact numbers, but I do know that the leaving domestic water was within a couple degrees of the leaving gray water and it was almost exactly halving the BTU requirements during said showers. Say it was something like 50 degrees in on the domestic and 78 degrees out, then 110 in on the gray and 80 degrees out. Or something like that. I really don't pay attention to my LP usage (used to have a meter but it was inaccurate) so I can't say for sure how much it helps as a dollar figure, but at 30 minutes a day in the shower with the above numbers it makes 15,000 BTU a day or 450k a month so it's fairly substantial in the grand scheme of things. Roughly $7 a month? I surely wouldn't pay what they want for a factory made one as it'd take 2 lifetimes to break even, but if you use a ton of DHW and/or have high utility costs it may very well work out in your favor

Tim Potter

found this:

https://www.homedepot.com/p/Power-Pipe-3-in-x-48-in-Drain-Water-Heat-Recovery-Unit-R3-48/203456041?source=shoppingads&locale=en-US&mtc=Shopping-B-F_Brand-G-Multi-NA-Multi-NA-Feed-PLA-NA-NA-Catchall_PLA&cm_mmc=Shopping-B-F_Brand-G-Multi-NA-Multi-NA-Feed-PLA-NA-NA-Catchall_PLA-71700000014585962-58700001236285396-92700010802552484&gclid=CjwKCAiAyc2BBhAaEiwA44-wWwZ_mgfyB64EqhwN8tU9pSEjauK6NDGtKeQHeddtAMyk_LqNVgddKhoC2AUQAvD_BwE&gclsrc=aw.ds

JakeCK

Tim Potter said:

found this: 

That is the one I refered to in my first post. Only I would need the 4" version for my stack.

Larry Weingarten

Hi, Here's a little background and thinking on these units: https://www.architectmagazine.com/technology/drain-water-heat-recovery-systems-are-energy-efficient-and-economical_o
The makers of Power Pipe here: http://renewability.com/ They have the answers to lots of questions on performance and durability.

Yours, Larry

PC7060

$850! Good grief, the ROI would be 20 years if ever.  

@JakeCK if your water is that cold, I’d recommend using the $850 to buy a indirect tank and install inline with the service input. It will allow the water come up to ambient using building heat. 

Or use a electric water heater (unplugged acoustic version).

Or stop by @Youngplumber place, he’s got a vintage 1985 beauty that would be perfect!! 

jumper

>>Double wall construction, with a positive and completely unobstructed path to drain from the space between the two flows would alleviate the concern. It would also, I think, reduce the heat transfer to pretty close to nil.<<

Ditto. Double wall requirements rendered a lot of energy conserving ideas useless. Does anyone know if heat pump water heaters use double walled?

JakeCK

PC7060 said:

$850! Good grief, the ROI would be 20 years if ever.  

@JakeCK if your water is that cold, I’d recommend using the $850 to buy a indirect tank and install inline with the service input. It will allow the water come up to ambient using building heat. 

Or use a electric water heater (unplugged acoustic version).

Or stop by @Youngplumber place, he’s got a vintage 1985 beauty that would be perfect!! 

Yet people spend thousands replacing perfectly good boilers/furnaces to save maybe 15% on their fuel bills, if they're lucky. And those have a tendency to fail much earlier and need a lot more PM.
I just got my gas bill for the past month, it was $172 and it has been a cold winter. I keep the house at 72 steady with no set back. Its heated by a converted gravity system and a 30+ year old ~80% weil mcclain boiler. I have original windows with aluminum storms, 2x4 construction no insulation, about 1500sq ft with full basement and walk up unfinished attic. Takes ~65k btu's to heat. If I plopped a 95% mod con in tomorrow I would have saved at best $25 dollars. I heat the house maybe 7 months a year. What's the ROI on that?

And how about the families that spend 10's of thousands replacing original windows with plastic ones that start failing in a decade?

Does this actually have a chance to have a real ROI?

Here are some other thoughts besides just raw roi with regard to taking a shower. What if you are installing a radiant heating system with a indirect DHW tank and you could could go with a size smaller boiler by using one of these recovery pipes? What if it meant the owner could also take three or four showers with a smaller tank vs two showers with the same sized tank? I would bet the cost saving of using a smaller source would almost pay for the pipe. And the best part? The pipe doesn't wear out like a hot water tank or boiler. 

JakeCK

Just ran a thermometer under the faucet. 41 degrees after letting it run for a few minutes. I'm sure once everyone wakes up on my street and the water starts flowing faster it'll get a little colder too.

PC7060

@JakeCK - thanks for the information.  I can see how the unit could be very effective if installed to preheated water feed the supply side DHW system.    Especially where you have a single stack that services multiple showers. Your point that the system could be used to reduce the size of the domestic hot water system is a good one particularly when dealing with very cold input water like yours feeding a tankless heater. 

A couple of the install examples showed the preheated water being funneled up into the domestic cold water, this makes a little sense to me.

Your points about replacing windows or upgrading heating systems are not very compelling in the context of this discussion. We could go on and on about poor decisions based on market or sales pressure.

Even the often cited replacement window example is not a black or white decision.  Years ago I replaced the single pane windows in house built in 1985 with high quality Weather Shield brand “sash pack”.  Great windows and very cost effective since install myself at few hundred bucks each without changing the look or character of the house.  My current project is a historic home and we are rebuilding 39 original Foucault process glass windows (aka “wavy”) to preserve the character of the home. Much more complicated than sash packs but the right decision in this context (especially since its what my wife wanted )