New York's Cooperative and Condominium Community

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Cutting Waste and Long Waits for Hot Water in a Nine-Story Condo

New York City

Domestic hot water, recirculation system, single riser, boiler.

New white pipes recirculate unused hot water to the boiler room, cutting water waste and fuel costs (image courtesy of RAND Engineering & Architecture).

Sept. 13, 2022

As part of our ongoing Problem Solved series, Habitat spoke with Peter Varsalona, principal and vice president at RAND Engineering & Architecture.

A recirculation problem. A nine-story condominium was having a long-term problem with domestic hot water supply to the apartments. It was taking 15 to 20 minutes or so for hot water to reach the upper-floor apartments, and approximately 10 to 15 minutes for hot water to reach the lower-level apartments. The biggest problem here was that they had no dedicated hot water recirculation system. They only had a single pipe of hot water supply for all 55 apartments.

What this means is that the hot water that's delivered to the apartments is sitting in the hot water supply riser until it's used. If it’s not used, the water will eventually start to cool down. Historically they had a much higher domestic hot water consumption in the building, and the water would be used and it would be reheated and refilled into that supply line. But what we found over time is that the hot water demand has declined and the water gets cool, and so unit-owners have to run their faucets or their showers a very long time to get hot water. This isn't a problem in newer buildings or older buildings that have retrofitted return systems. This building never did.

No quick fix. The fix is very complicated. In an older building where this hasn't been performed, you now have to open up walls and ceilings to access the piping. In some cases you may be disturbing materials that have asbestos in them. And then you're going to have to bring a line all the way back down to the boiler room and circulate it back to the mixing valve so that it can be reheated for hot water. You need to work in every apartment in order to make this work. And it was just so costly and disruptive that the condo board asked us to see if we could come up with something a little different.

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A lightbulb moment. We focused on the common areas. One retrofit they had done was to install a new domestic hot water main above the roof, in its own insulated enclosure. We thought, "Hey, there's an idea. What happens if we install our circulation loop alongside that line on top of the roof?" If we extended the hot water supply risers up through the roof and connected to this new loop that we would provide, we would then have something going. And we figured that if we installed that loop, we could then follow up with one master return riser back down to the basement, which could then be linked up to the mixing valves.

We found they have an open stairwell where we could run the main riser all the way down to the basement, without entering apartments. However, we still needed to connect from the top of the riser to the roof level overhead, so the ninth-floor apartments would be affected. When we looked inside the apartments, the risers were in chases (enclosures for pipes or wires), so we just had to open up the chases to extend the pipe up. It didn’t affect that many finishes, which had a big impact on timing and cost.

Big savings. Our initial estimates had the job costing several hundred thousand dollars if we had to work inside all 55 apartments. We were able to do the project for a little over $68,000. 

Waste not. You want to reduce the amount of time your boiler is operating to heat up water. It's particularly wasteful to have unused hot water that has to be constantly reheated at larger temperature gradients. If you're recirculating water, the maximum you're raising the temperature is maybe 10 degrees, which is not that significant. You're not wasting energy by continually heating colder water. So a recirculation system is a critical element to a building. And anytime you can save on fuel costs, it's going to help you long-term.

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