A This Old House segment where Richard Trethewey installs a heat exchanger that uses waste heat from a central air conditioner to heat a swimming pool.
Why Hacker News points people here: HN cites it as a practical demonstration of reusing AC waste heat, in threads about heat recovery.
“It's a stainless steel coil that you can put on your A/C and then run water from your pool over it to heat the pool.”HN comment, 2026
“Here’sa video from This Old House on installing one of the systems.”
Demonstrates installing an AC waste-heat pool heater
Full comment
Houses with pools should use the waste heat from their air conditioning system to heat their pool. Unfortunately, the system requires an HVAV technician, an electrician, and a plumber to install. I’m also not sure how many HVAC techs are familiar with installing something like that. Seems like a great energy saver though. Here’sa video from This Old House on installing one of the systems. this video
Cites itenerg8Apr 2020
“This Old House did a segment on linking the systems”
Segment on linking pool and A/C systems
Full comment
From my reading of heat pumps, mismatches in energy sources and sinks can make linking things together more complicated (aka more expensive) than is commonly available. For the pool <-> A/C case, This Old House did a segment on linking the systems: this video Edit: chris_va has more details about why linking systems is hard: link
Cites italexpotatoJul 2026
“It's a stainless steel coil that you can put on your A/C and then run water from your pool over it to heat the pool.”
Shows a coil on the A/C heating pool water
Full comment
This does exist btw. It's a stainless steel coil that you can put on your A/C and then run water from your pool over it to heat the pool. this video
