It can be done, but the advantage of a tankless heater is that you don't have to store heated water and lose energy due to inefficient insulation. A recirculating pump will decrease efficiency by storing hot water in the even more inefficient pipes instead of in a tank. Returning through the cold pipe means having to waste hot water whenever you use cold or mixed water. If you don't care about efficiency then it could work for you.

Good points. The selling point on tankless for us was the unlimited supply of hot water more than the idea of not reheating water we weren't using.

I see your point about wasting hot water when we want cold. It's kind of the opposite of what we have now--wasting cold to get hot. Maybe that's a vote for dedicated loop if I decide to recirculate.

Thanks.

Wouldn't a point of use heater be a much more efficient (and easier) choice?

Recirculating pump and you have a tankless water heater? .. .. .. Yea, NO.

You don't have hot water to recirculate. If you recirculate enough water to turn the heater on then you are heating water 24 hours a day in pipes that are not even insulated.

Smaller point use heaters are your only real option. I guess you could put small (tanked) water heater in bath and kitchen, but that kinda defeats the hole thing.

I’ve looked into one as well and the common use I’ve seen is putting the recirculating pump on a timer and set that for common use times like morning and evening showers and off at all other times. Depending on the pump, you can have multiple valves since each can run independently. Common complaints I’ve read about the cold line usage is it takes some time to get the cold water cold.

The ones I've looked at require 240V which would be a bigger deal. And would only fix the problem in one fixture.

Some tankless water heaters have language in the warranty fine print that voids or shortens the warranty if they're used in recirculating systems. They're not designed for that kind of constant duty.

You should consider point of use heaters (as other users have suggested).

I'm thinking more along the lines of a thermostatically controlled pump, perhaps in conjunction with a timer so that it only circulates at certain times of day. These are available.

A limited hot water supply is not a bad thing. It encourages conservation.

Personally, I would rather run the electric (assuming there's space in the breaker box) then deal with new plumbing.

I did misunderstand your post though. I thought that the kitchen was your main focus. Even if you are concerned about more than one fixture I would still strongly consider the point of use heaters. Or get rid of the tankless heater.

I probably wouldn't end up doing any of this. None of these options make good financial sense...but not everything we do in life needs to be the sensible thing.

I can’t believe this wasn’t said sooner. A recirculating pump makes NO sense whatsoever with a tankless heater.

EDIT: I should have looked into this before that comment. It looks that a recirculating pump and water return circuit can be used to return hot water into either an insulated storage tank, small tank water heater, or even another tankless; which in turn feeds the warm/re-heated water in series back into the hot water supply.

This would reduce the time needed to get newly heated water from the primary tankless to the fixtures, not a bad idea

Keep in mind that I would have the same problem with a tank water heater. That is, it takes a long time to get water at the fixture.

Space in the box is a concern.

I have a tankless hot water heater, and recirculating pump. But to work, it requires a small electric hot water tank. So… we get the best and worst of both worlds. Unlimited hot water and quick to the tap. But not energy efficient, and very costly. I’d rather just have hybrid hw tank

Right, but tankless+recirculation is a nonstarter in my mind. Your options are tankless and point of use on key fixtures or tank and recirc.

If you get one with a small tank for the kitchen sink, it can run off 120v. It'll be a heck of a lot more efficient than constantly recirculating.

For the bath as well, if you add a ~2.5 gallon 120v water heater in line with with hot water line, it'll give you hot water long enough for the water from your main water heater to arrive.

If you want to get some of the benefits of the recirculation system, put the pump on a switch (or even better, a timer switch) near the point of use. Flip it on a minute before you use the water, then turn it off and enjoy your hot water. You're not wasting water or energy then.

Unless your house is 30,000 square feet and the furthest faucet is 100 yards away from the water heater....you're talking 10-15 seconds at the absolute "worst plumbing job ever" case for hot water. Just turn the water on and wait... Recirculating a on demand water heater is about the dumbest thing I see on Reddit from time to time....

If you really see the need then put in as efficient a standing tank water heater as you can then recirc that. It'll be much better for the world and for your gas bill since that on demand uses a hell of a lot more gas when its running all day every couple seconds than a standing tank already insulated and hot. Not to mention you are going to chew thru that "MUch" more expensive on demand heater running it near continuous... to save you waiting a few seconds to get hot water at a sink...

Hey, I did recirculating pump through cold water lines in an upstairs bathroom. Basically the pump would run for one minute and it was on a Motion sensor. It wouldn’t run again for 30 minutes after initial run. Made it nice for instant hot water in the morning for a shower or washing your hands or whatever.

Some recirculating pumps have timers, so you set them to go when you most need it. Typically you run the circulating line ( hot of course) to the furthest fixture.

I was sort of thinking the same thing. Though a recirculating pump isn't all the efficient on a tank, but probbably way more efficient than tankless

This is the right answer ☝️

Yup, tankless are promoted for [energy] savings that really never materialize due to the extra cost compared to a ‘tanked’ gas heater. With unlimited supply, saving are literally down the drain.

Hybrid/heat pump heater makes a lot of sense if natural gas isn’t available. Otherwise it’s more of making a point.

When green electricity is available, I think hybrid electric tanks win. ?

But wouldn't you just be running the heating elements constantly?

The examples I saw the tankless would only be heating water when a faucet was running

So how does that get you instant hot water at the far bath?

Environment yes - but never on pure cost.

Some tankless water heaters have built in recirc pumps or have an option for an external pump. You do need insulated piping though.

If you do this, make sure you insulate both the delivery and return pipes to reduce the amount of heat loss on water returning to the water heater to be reheated. Also install a pump with a adjustable timer so that water is not being recirculated at unnecessary times

By locating the storage tank just ahead of the far bath.

Any time anybody runs hot water in the house, the recirculating loop warms up and fill the storage tank with hot water