Electric hot water "booster"?

The hot water tap in my (not-large) house takes a really long time to deliver hot water. I live in southern California and would rather not waste water this way. Is there such a thing as a small electric hot water heater that can temporarily warm it up until a sensor detects that the incoming water is in fact hot? I’m thinking of a unit like the tankless heaters that serve a whole house, but smaller and just for this purpose. Would it even be feasible/economical?

I’ve seen showerheads with built in (electrically powered) water heating in Brazil.

There is no efficient means to accomplish your goal.

You could plumb in a recirculation loop/pump. This continually circulates the hot water through the pipes so when there is a demand the hot water is already there and ready to go.

You could install a point of use electric heater, but those are mostly just handy for on demand hot water for tea and such. If you fed it off the hot water it would draw hot water through the pipes. They are pretty inefficient as they are like a mini water heater, they keep water hot 24/7

Anot on demand water heater is actually worse for on demand hot water as they don’t store hot water and it takes a minute of running water for them to come up to temperature. Once they’ve kicked in the hot water is limitless. They are more energy efficient, not water efficient.

Keep a pitcher next to the sink and fill it with the initial ‘hot’ watEric and use that to water plants. Let it go down the drain and it will get recycled.

You can add a pump to your water heater, so the heated water constantly runs between the water heater and the furthest sink or fixture.

We refer to those as suicide shower heads.

There are point of use water heaters with 2-10 gallon capacities that can fit under a sink. Most of the electric ones use 110V and plug into an outlet, though it might be good to run a separate circuit so that the breaker doesn’t blow when the heater is on and an air dryer is being used.

I’d just run it in line between the hot water valve and the tap, where it can keep a reserve of hot water until the hot water from the main heater arrives and joins the mix. There’s not really a penalty to hooking water heaters up in series; it’s what my master plumber brother used to do in his homes.

You need to look up mini point of use tankless water heaters. We installed one at our club and it works great. It goes on the cold water line and feeds a single faucet.


A small under-sink electric unit accomplishes your primary goal of saving water. I have one, and its 2.5-gallon tank holds plenty for me to wash all the stuff that I don’t put in the dishwasher (big stuff, delicate stuff, or stuff-I-might-need-again-before-I-run-the-dishwasher). Sometimes the tank runs out, but that’s only a little worse than not having the unit. (It’s a little worse because the fresh hot water mixes inside the 2.5-gal tank with the ambient-temp water that was in the pipe, so it takes a little longer for the stream to get back up to the hottest temperatures again. But it’s a minor thing, and I actually plan for it when I have a large washing task by staging up items to rinse.)

I don’t know about that but you can get something that installs under your sink that will pump water from the hot side into the cold side* and run until it sense hot water. Since they’re really designed for showers, many of them come with a timer so the hot water is ready to go at a predetermined time and I’ve even seen some that have a remote control so you can hit get it started from, say, your bedroom.

Here’s an example of a Hot Water Recirculating Pump. Looking very quickly, I see the price range from about a hundred dollars to over $600. I have no idea what the difference is, but they do look easy to install. A plumber/handyman type person could probably do it in under an hour.

*I know that seems like it shouldn’t work, but it does.

I have a 3 pipe system and love it. My water heater is in one corner of the garage. And the Master bath shower is in the furthest corner from the heater. It use to take 2.5 gallons of water to get hot water before a shower.

When remodeling the kitchen (under the master bedroom) I ran new water lines. Hot, cold, and return. The pump is in the garage at the water heater. I also installer a low voltage relay, buttons in the bathrooms and Kitchen, and a time delay switch set for 30 minutes. Push the button await about 2 minutes and almost instant hat water at the taps and showers.

My house is also a slab house with the water pipes under the slab. The builder used thin wall copper pipes. Before changing the pipes we had two under slab leaks. and just before tying in the upstairs a third leak. Now all the under ground piping has been by passed.

And he’s not kidding (About the term, not necessarily about your chances of survival, which seem surprisingly high.)

Is that reference based on any empirical data reflecting any loss of life attributable to their use? They re also in use in countries like Germany, which are even stricter than the USA about product safety issues.

We had a house in which the (relocated) master was a long ways from the heater, and I put a small electric heater under the sink. The smallest models fit well even in a small cabinet and you can usually tap into the adjacent socket, with a GFCI, for power.

I would put it on the cold water line, though, and essentally shut off/not use the long hot water run. Otherwise, all you’ll do with most hot water uses from that sink is pull enough hot water from the big tank to partly fill the line, where the heating will be wasted.

The only not-very-good solution for a shower is to put a bigger heater on that end of the house, and then you’re talking a permit, probably pro work, and the continuing expense of heating that much water. For me, having instant hot water for face washing etc. was enough; I could always wait 30-60 seconds for shower water.

This is what you want, not a separate hot water heater under your sink. The issue you have is not that the water can’t quickly flow from the hot water heater to your sink, it is that there is a lot of cold water in the way already in the pipes and your faucet can’t get rid of it fast enough. One of these pumps gets the cold water in the hot line out fast via the existing cold water line and you have hot water in seconds without wasting any water at all.

Recirculating pumps are one solution, but be sure to insulate all your hot water pipes well. Otherwise, you’re just running a giant and very inefficient radiator system for your house. Making it on-demand is better, but then all you’re doing is saving a few gallons of water each usage - an admirable thing, but the reality/efficiency may not warrant the expense and hassle of a circ pump.

The pump I mentioned is more of an “on demand” system, it doesn’t run constantly, you just (in one of a handful of way) run it right before you need it. It’s like turning on the hot water for a few minutes before getting in the shower to purge the cold water, but without dumping all that water down the drain.

The pump I put in at my old house has a thermostat. It turns the pump off at a certain temp then back on when it drops to a certain temp. It also has a timer, much like a Christmas tree timer, that lets you have it shut clear off during the night and/or during the day if no one is home. I actually got it because the pipes kept freezing in the winter if we forgot to leave them dripping. (The kitchen floor was very close to the ground, and the sink very close to the outside of the house. It used very little electricity, and the only drawback is the cold water runs warm for a few seconds, but it takes less water for it to cool down than it took for the hot to warm up.

I have one of these systems in my master bath. I press a button and water from the hot side is forced into the cold side. When the hot water arrives the pump shuts off. Slight downside is that if you then want to take a pill, the cold water is slightly warm.

JoeyP, I don’t get how the pump you describe works to save water. Can you explain slowly with small words?

Electric showers in Europe (I have this one) are a very different kettle of fish to the “bare wires in the showerhead” South American variety.