Anyone built an Instant Hot Water system?

Looks like the way this one works, when the timer is sets the unit to 'on', the motor always runs and creates a pressure differential between the hot line and the cold line (it pressurizes the hot line relative to the cold line).

Then, the sensor-bypass thing is a thermostatic valve that just lets water pass from hot to cold as long as the 'hot' side is below some set temperature.

Neat! Wastes some energy in the pump, and having the hot line always 'hot' wastes some energy too.That's arguable if the pipe is in a space you'd like to heat, since the wasted heat will just go into a space you're trying to heat anyway.

It looks like as long as you have only one hot water heater, you only need one pump, and can add the bypass valve to multiple faucets. If your hot line from the heater branches, you put the pump before the branch, and then install a bypass valve at the end of each branch.

If I was going to build something, I'd prefer the pump that sits at the end of the line, and only activates when you push a button. The pump runs until 'hot' water shows up. Hit the button on your way in, when you're ready to wash up, the water's warm. If you're heading in to just use the hot water, you still have to wait though...

Anyway, the pump you linked to looks like serious overkill- you want something that can tolerate no flow ( a blocked pipe).

Dave

Hi Dave,

The way I understand it to work is that it turns the pump "ON" when the low temp sensor detects 85deg. The pump sucks cool/cold water from the hot line and pushes it into the cold line which in turn goes back into the heater, closed system. When the "OFF" sensor detects 95deg it turns the pump off.

I believe the timer is to stop circulating during un-needed times like between 11:30pm and 5:00am.

The way my system is here I would need two pumps or another 200 feet of pipes for the second sensor with that commercial system. I'd also have top lag all those pipes. Tooooo hard.

Dave

Why not just let the water run until it gets hot? Should take no more than a gallon and costs zero to set up and wastes no energy until you need it ;)

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The systems that I have seen depend on natural convection. The main hot water pipe is ran under the floor, and a smaller return pipe is ran along the ceiling. Any of these systems are huge energy wasters.

Vaughn

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That's why I favor the one that pumps the cold water from the hot line into the cold line only when you push the button. The 'hot' line doesn't stay hot when you don't use any hot water.

It wastes a small amount less energy than just running the water because the 'cold' water you're pumping into the water heater is (probably) warmer than water drawn fresh from the mains, or from the well.

Dave

Hi guys,

Thanks for th thoughts...

Dave, that is no different to running the tap other than it will happen faster. I would still be putting a slug of hot water between the water heater and the tap. The only thing is I would not be wasting the water and that is not a huge concern with a well.

Looks like back to plan A, run the tap.

Dave

I recall a demand based pump from 20 years or so ago. It was attached between the hot & cold lines at the farthest point of use from the water heater. When a sensor detected a drop in the hot line pressure the pump would turn on and pump from the hot line into the cold line until another sensor detected that the hot line temp was up to some setpoint. The thing was fully automatic, no timers, no manual switches, and would trigger if any hot faucet was momentarily turned on. I can't remember the name or manufacturer. Googling is left as an exercise for the OP. Art

"Dave, I can't do that" wrote >

Hi Art,

Hmmm, seems a better system than the current one with timer a timer. I guess a timer costs less than a flow switch.

Dave

If this was my house with a long-pipe problem, the timer would be a

15-minute wind-up Intermatic. You wake up and start your morning ritual and allow 5 minutes for the pump to get the hot water to the far end (without wasting any water down the drain) and then hop in the nice hot shower.

If you keep the hot water pipes hot all the time with a circulating pump at the far end, you waste a lot of the energy savings of an instant water heater - as in, the system isn't supposed to be heating the water /at all/ except when it is actually being used. Might as well go back to an old style storage tank heater.

We split the house in two a long time ago, so there's no longer one big electric water heater (and to raise the stupidity level it was in the attic...) but two medium sized gas water heaters, one at each end with fairly short runs.

One has 1 and 1/2 baths, the other has one bath, laundry, laundry sink, dishwasher and kitchen sink.

First one that dies gets replaced with an instant - the kitchen and laundry end gets the "large" unit, the 1 and 1/2 bath end can get a "small". And during the process we can use the shower that still has hot water, so it doesn't have to be done /right that moment/.

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