Does a recirculating pump defeat the purpose of on-demand water heating?

[plowhog]

Would you want to push a button every time you want the furnace heat to come on, or would you rather have it be automatic?

The flip side is that recirc system would be the only energy using device in the home that is not controllable. Your furnace/AC has a thermostat so you can turn it off when you leave for work, go on vacation, etc. Your lights have switches-- hmm why not leave them on all the time to eliminate the bother of a switch?

If we were populating the home with a family full of children, etc. then I see having recirc always going being an advantage. But it's only my wife and me, and we sometime travel to other places. So why burn electricity (pump) and propane (burner) to keep a water loop hot while we are not even at home? That is my objection.

This is new construction so a recirc system *will* be plumbed in regardless of how it is used. If my wife and I could use the button method but have the system capable of doing automatic recirc in the future, that would be ideal. When we sell, a family will likely inhabit our home since we have plenty of bedrooms and space.

I've set a meeting with the plumber to discuss all of this.

One more thing: apparently the undesirable lag before hot water arrives at the shower head or faucet is being amplified by the low flow energy saving fixtures. When you have a 2.5gpm shower head, it takes longer to evacuate the cold water out of the supply pipe than if you have one of the old "blaster" shower heads that pushed through a lot more water.

 

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The flip side is that recirc system would be the only energy using device in the home that is not controllable.

My recirc is on a "smart outlet"; I can change the schedule with my phone very easily.
Before I had the smart outlet, when we went on vacation I'd just go to the utility closet it's in and turn it off.
My wife having instant hot water at 0430 in the winter is worth every penny.

 

[MossRoad]

I like the idea of having the recirc pump come on as soon as the light is turned on in the bathroom, kitchen, etc... then timing out eventually. That seems to be a good compromise between energy efficiency and the opulent luxury of instant hot water.

 

[Lelandwelds]

I had an acquaintance who had a sprawling 5000 + square foot house. Nothing mechanical was really centralized in wet wall or mechanical room. His stuff was in the garage and one of the master bedroom closets. He had a huge tankless with an extra thermastat that was fed by an electric tank heater. He had some automation stuff and a computer that logged and controlled things. He had big servers and could play music or movies anywhere. It was tied into a camera and security system too. I had never seen anything like that in person. Complicated but cool.

His circulator was activated by two infra red detectors, one in the master bath and one in the mother in law suite. Walk into either and it started timed pumping. His place had six bedrooms or so and an upstairs game room with a closet that had six bunk beds. His place could sleep thirty or be vacant. He claimed to never run out of hot water.

Two stoves. Full bar with two kegs on tap. Four ovens. Two dishwashers. Two double sinks. Drawer frig or freezer by the ovens. Two refrigerators. Two upright freezers. Multi level deck. Outdoor kitchen and fireplace. Outdoor projection tv.

He liked to show it off. But no pool, no garage, no shop, and no tractor. His priorities were a bit out of wack.

 

[Pinzgauer]

The flip side is that recirc system would be the only energy using device in the home that is not controllable. Your furnace/AC has a thermostat so you can turn it off when you leave for work, go on vacation, etc. Your lights have switches-- hmm why not leave them on all the time to eliminate the bother of a switch?

Missing the point- most recirc pumps are not wired 24x7, in fact it's not recommended.

They are nearly always timer, motion, light switch, or even demand triggered.

Many have internal thermostats which bypass the faucet and backfeed via the cold line until the water is up to temp so water is not wasted. Some are smart enough to detect when the faucet is opened and trigger the recirc.

With a recirc pump even a long run is hot in a minute or less.

My favorite setup is to add a switched outlet under the sink that is tied to the light or fan switch. Water is hot by the time you've done your business. Leave the lights/fan on when multiple folks are running through the shower and it stays hot. Or use a motion sensor with 15m delayed off to do the same.

The good recirc pumps are not cheap, but really eliminate any disadvantage tankless has.

Some folks (offices, busy houses) put a small plug in tank heater under the sink to cover the time while the tankless is feeding. Once the tankless water is available the tank heater shuts off.

I also see folks do small under sink 110v tankless in series with often used faucets. Again, they turn off once the main tankless is up to temp.

Many potential solutions.

 

[Pinzgauer]

I like the idea of having the recirc pump come on as soon as the light is turned on in the bathroom, kitchen, etc... then timing out eventually. That seems to be a good compromise between energy efficiency and the opulent luxury of instant hot water.

It's my favorite solution and is simplest. If the bath has a separate fan, I'm inclined to wire it to that, as you can leave it on with lower power. (maybe not so much lower now with LED lights)

 

[MossRoad]

It's my favorite solution and is simplest. If the bath has a separate fan, I'm inclined to wire it to that, as you can leave it on with lower power. (maybe not so much lower now with LED lights)

Yeah, I've got a 6 or 7w bulb in my overhead bathroom and it's quite bright. There's also a three bulb fixture over the double medicine cabinet and sink with three 4w bulbs. Almost too bright. LEDs are really coming along.