Finally! A decent alternative to hot water recirculating loops

Amy Musser

I’ve never been a fan of hot water recirculating loops. I feel like they’ve been oversold as a “green feature” and a few particularly bad ones have resulted in really frustrating energy complaints for my clients. Although they do provide some water savings, they’re more of a convenience feature and a way to deal with a plumbing-blind design in a big house.

My biggest problem with recirculation loops is that they inherently use more energy than a compactly designed traditional system. All the ways that they use more energy can be badly done and make the system worse, but even a good design will use more.
• Pump energy: The worst systems use a constantly running pump. Demand-controlled systems (with buttons or occupancy sensors) improve this considerably, but the pump energy is never zero.
• More/bigger piping: You often end up with water passing through more pipe of a larger size than it otherwise would to get to a fixture. The better systems limit the size of piping in the system.
• Pipe insulation: Even if the pipe is insulated, it’s probably only R-2 (at best, maybe R-5). Given the small diameter of the piping and the low R-value, the loop water is going to lose heat a lot faster than it would if it were kept in a water heater. The worst systems (with constant recirculation) act like a small heating system for a house. That’s unfortunate because the water heater usually isn’t as efficient as the home’s main heating system.  It also fights the air conditioning system in the summer, so you pay for both heating and cooling.

I’ve encouraged my clients for years to design homes that avoid the “need” for these systems. Compact plumbing design is the best way: fixtures that use hot water are grouped close to the water heater so that the pipes are short and no one has to wait too long for hot water. In a big house, it may be that there are multiple compact-plumbing “groups”, each with its own (preferably tankless) water heater. Why doesn’t this happen? Two reasons. Designers who don’t think enough about plumbing proximity and builders who are trying to cut cost in a way that the homeowner won’t see. By the way, that’s not a dig on builders. Homeowners want them to cut costs, but not on the visual stuff. They don’t care how long it takes to get hot water until later, and most of them don’t understand the energy implications.

Manifold plumbing systems can also help. In these systems, every fixture has its own home run. In homes where the most frequently used fixtures can be located close to the water heater, it might not matter much that the guest bedroom has to wait for hot water.

Fortunately, there is now a decent alternative for those times when you’re stuck with a house that needs to have hot water on-demand, and where none of these other strategies will solve the problem. It’s called the D’Mand Kontrol, and it works a lot like a recirculation system for the homeowner. Conveniently, it can be easily retrofitted into existing homes.

With the D’Mand Kontrol, you install the plumbing as usual. The system includes a small pump that goes under the sink in the bathroom furthest from the water heater. You get buttons to press for hot water in every room with hot water (these can be wired or wireless). When the homeowner needs hot water, they press the button and the pump moves water from the hot water line into the cold water line under the bathroom sink. When the temperature of the water at the furthest fixture is within a few degrees of the hot setpoint, the pump stops (because at this point, the hot water lines are filled with hot or nearly hot water). You get all the water savings of a recirculation loop, with no more energy used than would be needed to feed faraway fixtures without the loop.

The systems are pretty affordable (under $1000), and dovetail nicely with the newer energy codes. They are a really nice solution. The only complaint I’ve heard was one homeowner who said he didn’t want to have to push a button for hot water. Picture me staring at him from over the rim of my glasses and saying, “Then let’s specify 3 tankless water heaters. Where would you like to put them?”

Copyright 2015.  Amy Musser.