this post was submitted on 19 Jun 2025
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In fancy installs, the hot water supply is a loop, not a tree, and a circulating pump keeps the entire run hot.
That sounds like a great way to waste energy.
Sorry, you've met wealthy people, right...?
It's just dumb engineering to heat up a pipe the entire day for the 0.8% of the day you need it to be hot.
Insulation + retaining heat means it isn't nearly as energy inefficient as you think.
They keep the water tanks heated all day, and not heating the pipes means they have to do more work as they are drained of more water to fill the length of pipe to the shower which will then lose that heat over the course the day, only to need the water heater to heat it back up again.
With enough insulation, anything can meet energy-efficiency standards. XD
Have you read the previous comments? Because that's exactly what's implied.
Heat pumps generally use a lot less power. Don't need to heat up much if it is already slightly hot.
In modern ones they learn patterns about hot water usage, so they are only active on max during the "busy" periods.
It’s typically used for large complexes like campuses where the hot water is made en masse in one building and the loop goes around all the other buildings. Helps keep cost down (at construction) because you only need one giant water heater. Helps not have to wait 10 minutes to bring the hot water to your building. Energy still gets wasted but given the number of users, not that bad.
Someone else already pointed out that these are usually pretty well insulated systems that don't radiate much energy, but also consider how many dozens of gallons of water aren't being wasted by waiting for it to be warm.
Nearly all of these systems are put on timers. So they stop cycling while you're at work or over night. They'll often make it a part of the smart home ecosystem as well, so you can override from a smart home device or phone
If you have a hot water tank, that hot water is just sitting there getting cold just waiting to be heated up again. A circulating pump puts that hot water to use by circulating it through the pipes, which has a nice side effect in cold climates of preventing the pipes from freezing and bursting. I doubt it wastes much energy as you think.
Hot water tanks do not just “get cold”; they are fantastically well insulated. And a great way to lower peak energy usage by accumulating heating power, making it possible to use a heat pump to heat the water.
Hot water tanks are usually not that well insulated. If you want to save electricity an easy thing to wrap a good later insulation around it.
Rather than just dumping the cold water down the drain?
A huge amount of waste https://www.youtube.com/watch?v=67i4-_sXGcQ Claims $400/year, $35/month.
In Finland if it takes more than 8 seconds for hot water to reach the furthest faucet then you're required by building code to have hot water circulation.
that makes sense, in Finland’s climate, heat lost out of the pipes is not wasted – it would heat the dwelling. not a big deal compared to dumping 20 wasted litres down the drain for every shower.
It's not just to save water. It's to prevent bacteria from growing. It doesn't grow well in cold water nor in hot water but it loves warm water.