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How much does shower use matter for drain-water heat recovery?
Drain-water heat recovery seems most promising when there’s a long vertical drain run and hot water is going down the drain while a shower is running. But I’m not sure how much shower frequency and duration change the practical benefit, or how much a short or hard-to-access drain section limits it.
I’ve also seen systems described as preheating incoming cold water, while others are connected to the water heater. Does that difference affect which hot-water setups they suit or how much plumbing work is involved? What installation constraints or maintenance needs tend to make the energy savings less worthwhile?
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2 replies
I’d give frequent use more weight than an occasional very long shower: recovery is useful while hot shower water is flowing down the drain and incoming water can be preheated, so that overlap happens repeatedly. A long shower still helps, but I wouldn’t assume one unusually long use outweighs regular shorter showers without knowing the actual flow and system layout.
The key difference is where the preheated water is routed: it may serve the water heater, the shower’s cold supply, or both, depending on the system. An accessible cold-water line near the drain may make one route simpler; reaching the heater may mean more rerouting. I’d compare the pipe runs and access in the specific installation rather than assume one connection suits every setup.
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