For those of you who are conducting residential energy assessments; are you recommending "on demand"  hot water re-circ. systems?  I'm finding that many of my customers waste a ton of water while they wait for the hot water to arrive. This is the case even with an insulated pipe because the water is simply wasted down the drain where as a properly configured re-circ system will return the water in the pipes to the water heater.  I recently became aware of a re-circ. system called Switch2o at www.switch2o.com that is enabled when the light switch in the room is thrown. It claims to waste only a cup of water and produces water saving far in excess of dual flush toilets. Thoughts?

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With PEX/manifold systems that are very popular these days, I don't see how the system would even work.

depends on the setup - with a homerun to each sink, tub, etc... you would have to install a pump at each location you want

With a manifold to manifold config (each bath is on a smaller manifold right there at the bath) or a homerun feeding a single bath via branches one pump will recirc the water for the whole bath

One pump. Activated by the light switch from each station.  Automatically shuts off when hot loop is recharged.  Puts cooled down water back into the water heater.

Definitely requires a tank, a lot of people are moving to tankless.   Also requires mechanical plumbing/sensors and a dedicated switch at each station.  Might be a complicated and touch, very niche, thing to sell.

Good luck.   

Navien has a fantastic condensing 98% efficient unit with a buffer tank AND pump, with internal recirc that can be programmed for when most likely needed AND can be connected to an external recirc loop.  That's the setup I'd recommend.  

I don't know much about those Navien units, but the last one I was around (worked in the house for a week) seemed to be whirring and clicking and cycling and running almost constantly, with no one home. Obviously there are a lot of variables, but this one was definitely using power and gas all day, and the owner is aware that it's a problem. For better or worse they haven't asked me to do anything about it. I had almost the same experience in another home... no one there, water heater chugging away.

They have very specific instructions, that it seems many installers are incapable of comprehending, which lead to problems. These are not plug and play devices.

I've seen too little gas volume, water volume, intake and exhaust issues, super hot settings, buffer turned off, buffer on 24/7, etc...

You can't have a high school biology student perform brain surgery, and that sometimes what you get when these go in. One test; ask the installer how many installed. Ask if he has the area reps number programmed into his phone. Then if he has a dual port manometer. If no, get a different installer.

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