Drain water heater recovery location
jeffodonnell
| Posted in General Questions on
I was considering installing a drain water heat recovery device in my new build. However one of the overlooked details is that the drain it would have to be located on will be across the hall and 12 feet or so away from my hot water heater. Should these details keep me from installing one?
This is a slab on grade and will be serving the bathroom that my four kids will be using for the next 15+ years. Thanks. Jeff
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Replies
As long as the output pipe to the WH is insulated, it should work just fine.
The output of the heat exchanger is tepid, not hot, no insulation required. I don't think I've ever measured the output of mine at more than ~80F, and that would be in the summer when the incoming water and the basement tempertures are at their warmest. The amount of heat loss to a room that's only 10-15F cooler than the pipe isn't much, if it's only 12' of pipe.
Mine is a 4" x 48" PowerPipe that tests about 50% recovery under NRCan test conditions.
Good point. I would say if the pipe goes through cooler unconditioned space, such as an unheated garage/basement/crawlspace, where the temperature difference would be greater, then insulating might still be viable.
Maybe it's viable on a 12 foot run over a 20 years if you're taking 25 showers in a row or something. A family of four showering daily is still only running it about about 30-35 minutes/day, and even in 50F basement the distribution losses are well under 1% of the total input energy. The insulation does nothing for the abandoned heat loss in the pipe at the end of a shower unless the next shower occurs within 30 minutes.
While the ideal would be to have it all clustered in one tight location, being 12' away is not a big deal. In 12 feet of 3/4" pipe there's only about quart of water, so at 8 quarts per minute (2gpm) at the shower head, 6 of which is from the water heater that's about 10 seconds of flow. Most showers run much longer than 10 seconds and even a short showers are longer than 100 seconds, so the delay and total amount of abandoned pre-heat in that 12 feet of pipe are negligible, whereas it it were 120 feet it would matter.
The output of the heat exchanger should be going to both the cold side of the shower, and the cold input to the water heater. Sometimes/often there will be a convenient place to just tee into the cold distribution plumbing upstream of both.