Copper Heat Recovery Coils

Alacrates's picture

These copper heat recovery coils (picture attached) are required in all new homes now where I live.

They circle the cold water entering a hot water tank around a portion of the drain pipe from the main shower in the residence, so that the fresh water entering the tank absorbs some of the heat of the waste water from a shower as it's draining, saving energy for heating the fresh water.

When I did my last level of plumbing school, we did the calculations for recovering the costs of the coil with the savings in heat energy, and it worked out for a family of four that the cost of the coil would be recovered after 3 - 4 years of use, on average.

From an environmental perspective though, I'm left to wonder if all the costs related to the mining of this copper and the manufacture of the coil have been included in these calculations. Copper is a finite, diminishing resource, is this really the best use of it, to recover a bit of waste heat from shower water? It could be, I just wonder. Especially where I live in Manitoba, Canada, most of the hot water tanks use hydro electric (though there are still quite a few using natural gas) - though I know from this forum, that if we use less electricity in MB, it can be sold into the U.S., reducing the amount of fossil fuels burned there to generate electricity.

On the other hand, thinking about the salvage economy envisioned by JMG, maybe these heavy copper coils are a good idea? Basically they use a good chunk of copper mined when the economy allows for such things, and sits it in houses to be recovered in some future time when it's needed to be melted down from scrap, and the drain easily replaced with plastic or cast iron pipe... Sort of a materials savings account spread throughout the community... (!)

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David Trammel's picture

Sure wish my hot water heater was that close to the shower. Here they put it right at the wall where the cold water line comes in from the street, then run hot water lines (copper with no insulation) across half the house to the shower and then a another 5 feet to the sink.

Looks like the part of your down pipe under the coil is also copper.

Alacrates's picture

Yeah, sometimes I guess they don't think a lot when they place the hot water tank originally. I never have much say when I'm installing them, I usually just have to put them somewhere in the maintenance room, in a corner left free after the furnace is in place.)

Yep the whole thing is copper, basically a 3" copper drainage pipe with 1/2" water pipe wrapped around it to absorb the heat of the water.

We don't have anything like that system to capture waste heat; I wish we did! And yes, it's probably a good idea to have ready-mined copper all over the place for the future.

One other thing you can do to capture waste heat with your water lines is to insulate the pipes. Pipe wrap insulation is long, long slit tubes of heavy foam insulation. The slit lets you fit it over the water lines. It comes in two thicknesses. The thicker one costs more but also keeps the water hotter.

I wrapped ALL our lines, everything I could reach, and it made a huge difference in the temperature of the water reaching the far sink (40 feet away from the hot water heater), the basement shower (20 feet but through cold space), and the upstairs shower (35 feet through an unheated attic). I'm not good at guessing distances so I may be short in my estimates.

I wrapped ALL the lines, both hot and cold but for different reasons. The hot water got the thicker wrap, keeping the water hotter.
The cold water lines also got wrapped, using the thinner wrap. Why wrap cold water lines? So they would take longer to freeze in the event we suffer an extended power outage. Frozen, burst pipes are a big, expensive enough problem to be worth the cost of multiple packages of pipe wrap.

In addition, as I was wrapping the pipes, I used red and blue electrical tape to wrap around the lines to identify hot (red) and cold (blue) water. The last touch was tagging (like the Navy does) to identify what that mysterious valve was and where that set of lines actually went.

It's a messy, tedious job but future homeowners and plumbers will appreciate my work. It made us more comfortable at once and the savings in hot water probably paid for the insulation after a few years.

You can get pipe wrap at any big hardware store like Lowes. Many places also sell preformed elbows which make turning those corners far, far easier.

Teresa from Hershey

Blueberry's picture

Smart to wrap the cold water pipe so the water entering the hot water tank is warmer also the cold water going to the control valve is warmer so it takes less hot water to have a nice hot shower. Now that is being a Green Wizard. edit for spelling

Alacrates's picture

I really like that you colour-coded the hot & cold lines and labelled the valves! That does make things easier for future maintenance, whoever is tasked with it.

On insulating cold water lines, a few different things to think about: if you get your water from deep in the ground, your cold water can be pretty cold, insulating your cold pipes is kind of just keeping this water really cold... but it does really help with condensation in the warm weather... I've gotten service calls from people calling in for leaky pipes, and it was nothing more than the condensation from hot air on cold water pipes, it can save a service call!....

One tip with the foam pipe insulation, we never buy the pre-formed elbows and tees... if you have a square with a 45 degree angle on one side, if you cut across the straight insulation with an exacto-knife at a 45 degree angle, the two pieces you're left with will fit together at a 90-degree fitting perfectly, I use black electric tape to cover over the seams...

David Trammel's picture

Great suggests so far, especially the color coding.

I wonder in the overall, whether you can recycle the energy from the shower better by just letting the water sit in the tub until it reaches ambient air temperature. You probably don't get much energy off that down pipe if its just catching the energy from falling water. Its past and gone before doing more than just heating up the pipe wall.

You'd also be able to recycle most of the gray water for plants with a small bucket.

Does look cool and probably employs people manufacturing the wrapping pipes and the people installing it, but you'd be better off having a standing tank, or making the down pipe into something similar to the flue in a Russian masonry stove, which goes back and forth horizontally while it goes up.

Great thought provoker, thanks for posting the picture Alacrates.

Yes, the bathtub full of water lets heat escape if you leave it sit.
You just have to keep kids away since it's a drowning hazard.

Teresa from Hershey

Alacrates's picture

Definitely, for a bath, letting the water sit until it reaches the ambient temperature of the room will recover the heat that your water heater put into warming the water, and reduce your space heating energy expenditure. Good caveat from Teresa mentioning that the standing water could be a hazard if young children are around.

Of course, in an air conditioned space, the heat is working at cross purposes with the refrigerants, drain that hot water as quick as possible! hehe

Showers are so common where I live (I don't personally get it, I like to take baths and soak in the heat) and according to the Manitoba Hydro, these copper heat recovery coils can reduce the energy a hot water tank consumes by 25%. Hard to believe, but draining water does tend to hug the surfaces of the pipe, and copper is a good thermal conductor. https://www.hydro.mb.ca/your_home/water_use/drain_water_heat_recovery/

I've never seen them, but I think I've heard of devices which collect the hot water draining from a shower/tub in the basement of a residence, and drastically slow down the hot water drainage, exchanging most of the heat into a basement before the wash-water trickles out into the sewer. I tried to look up these on google, but I can't seem to find any at the moment. I remember the idea from when I lived up north in the Yukon, they tried installing a lot of these, but apparently the sewers started to freeze up as they were receiving a lot less warm water!

As for the grey water from the tub, definitely a lot that can be done there... maybe that could be saved for a different post, I have a lot of ideas on this topic!

Why don't we insulate bathtubs with hard foam?
I had access to our bathtub in South Carolina. This was decades ago when Great Stuff (waterproof, expanding foam insulation in a spray can) still expanded to ten times or more. I sprayed every part of the underside of the bathtub that I could reach and what a difference!

That bathtub was never cold again and water for kid's baths stayed hot far, far longer.

Teresa from Hershey

Alacrates's picture

Yeah, there are huge cavities on the underside of most bathtubs, I'm wondering why we don't insulate that space... even if you didn't want to go with spray foam, you could stuff some regular fiberglass insulation into the gaps, and drastically slow down the heat loss... great idea!