Point of Use Hot Water Heater Questions

[Alex Zeller]

What options do you have? Can you run a new return line for a circulator pump without a lot of work? I personally would not send hot water back down the cold water line. I don't know about other people but I like my cold water to be cold. Also you may find that your shower is now too hot until cold water flushes all the hot water out of the line. Can you run a new circuit? If so a tankless on demand heater would be your best option. If the heater can't heat up cold water as you use it you are going to have a hot shower that turns cold before to gets hot again as the slug of cold water between the storage tank and the POU heater makes it's way up to the bathroom. Since it's an upstairs bathroom I would think that your options are limited.

[Bill George]

o if you feed the POU tank from the hot water line, where is the cold water that's in the line going to go? If you only need a little hot water, it will be fine, but once the POU tank is empty, you'll have cold water again until the hot water arrives from the main tank, because the POU heater won't heat the water quickly. Might not be an issue for a tub, but not what you want for a shower.

The cold water line IN on the POU water heater connects to the existing Hot water line. The output connects to the hot water faucet. The 2 or 3 gallons of water in the POU tank should be enough until the existing hot water arrives.

[Paul F Franklin]

o if you feed the POU tank from the hot water line, where is the cold water that's in the line going to go? If you only need a little hot water, it will be fine, but once the POU tank is empty, you'll have cold water again until the hot water arrives from the main tank, because the POU heater won't heat the water quickly. Might not be an issue for a tub, but not what you want for a shower.

The cold water line IN on the POU water heater connects to the existing Hot water line. The output connects to the hot water faucet. The 2 or 3 gallons of water in the POU tank should be enough until the existing hot water arrives.

For the sink, maybe, but for a shower you're going to have 2 gallons of hot, then 2 or so gallons of cold (that was in the hot water line between the big heater and the POU) then hot again. Not good for a shower.

[Jason Roehl]

For the sink, maybe, but for a shower you're going to have 2 gallons of hot, then 2 or so gallons of cold (that was in the hot water line between the big heater and the POU) then hot again. Not good for a shower.

He already mentioned that it’s 60’ of 3/4” pipe. There’s about 0.025 gal/ft at that size, so just over a gallon. It’ll blend in with the hot water in the POU tank as he uses it. Most people have their water heaters set high enough that they have to blend some cold in with the hot for their showers anyway, so the usage from the POU heater will be slow enough that the incoming slug of room-temperature water from the main water heater shouldn’t draw down the temperature of the POU heater much.

[Jerome Stanek]

I think you might be over thinking it.
You have hot water, you just need to get it to where you need it.

A circulator pump keeps hot water on demand at the point where you install the valve. There is no need to wait for water to warm up, no waste, no extra tank, minimal plumbing skills, customizable timer, cheap to run

JMO

That is almost true but the advantage is where you put the valve. I put mine on the last sink inline and all the other sinks and tub shower have hat water almost instantly. There is a timer so you can set it to shut off the hot when it is not needed like if no one is home during the day or late at night it sets in 15 min increments. I have not notice a increarse in my gas bill since I installed it. and you do get the advantage of more hot water as the pipes are always full so you use less water.

[Bill George]

For the sink, maybe, but for a shower you're going to have 2 gallons of hot, then 2 or so gallons of cold (that was in the hot water line between the big heater and the POU) then hot again. Not good for a shower.

But your not using straight 140 degree hot water when you shower, its tempered with the cold water.

[roger wiegand]

A temperature sensing (vs flow sensing) on demand heater is a good option in this situation if you have the electrical capacity readily available. A circulating pump that runs continuously is very wasteful of power, a little for the pump a lot for the hot water heating (and more if you're radiating extra heat inside the house during AC seasons). A circulating pump with a switch at the POU (with an automatic shutoff so it doesn't keep running) is also a good choice.

[Bill George]

Those circulating pumps are very small, very little current draw and both lines are or should be insulated so little or no heat gain to the house. A on demand water heater costs $1200 plus and then the huge 230 volt service to run it makes it not practical. The little 115 volt point of use heater ($200-$300) in series with the existing hot water line only heats and holds 2 or 3 gallons of water in a well insulated tank.

This pump uses 10 watts > https://www.supplyhouse.com/Goulds-P...d-1-2-Threaded

Installing> https://s3.amazonaws.com/s3.supplyho...structions.pdf

[Perry Hilbert Jr]

Because of the way our house was built, the hot water travels 40 feet to one end and then up stairs and 40 ft back to the master bathroom. So the hot water to the master bathrooom takes a long time. However, there are several hot water using things along the way. So in the morning, I run the dishwasher and maybe a load of laundry, about the time Mrs. gets up to shower for work. Just that gets the hot water half way through the system before she gets to the shower. We use the hot water side of the master bathroom sinks to start washing, shaving etc., that also gets the hot water closer.

[Bill George]

Because of the way our house was built, the hot water travels 40 feet to one end and then up stairs and 40 ft back to the master bathroom. So the hot water to the master bathroom takes a long time. However, there are several hot water using things along the way. So in the morning, I run the dishwasher and maybe a load of laundry, about the time Mrs. gets up to shower for work. Just that gets the hot water half way through the system before she gets to the shower. We use the hot water side of the master bathroom sinks to start washing, shaving etc., that also gets the hot water closer.

Put in a pump, see the instruction manual I linked too above.

[Jack Frederick]

Are you able to install a recirc line? Taht would be the hot set-up. I just don’t care for the pump back into the cold line for reasons noted. Grundfos makes a nice set-up for recirc with the timer mounted on the pump. It seems a shame to waste the energy by running it 24/7. The house we just sold had a wireless control on the Rinnai water heater. I had motion sensors up in the corner of the bathroom ceilings and a push button mounted up under the cabinet next to the kitchen sink. When entering the bathroom the pump made and in a few seconds I had hot water. The key is to have a strong wireless signal. If you have wonky wireless it is a pitn. It worked well in our case not wasting water, energy or time.

[Edward Weber]

I've been using one, like the one I linked to, for 10 years, no issues what so ever.
The claim about hot water on the cold side is a bit overblown IMO.
Yes you do get lukewarm water for a bit on the cold side but the entire point of the product is to get hot water to that point. If you want ice cold water in the bath, you may need another solution.

[Stephen Tashiro]

The POU heater is going to require a 15 amp circuit just for the heater, most have 1400-1500 watt elements.

Do the tankless kind of electric water heaters only require 15 amps? I thought they usually have a higher peak amp draw.

[Bill George]

Do the tankless kind of electric water heaters only require 15 amps? I thought they usually have a higher peak amp draw.

This is a small point of use with a 2 or 3 gallon tank that's all. Not those whole house ones.

[Alan Rutherford]

He already mentioned that it’s 60’ of 3/4” pipe. There’s about 0.025 gal/ft at that size, so just over a gallon. It’ll blend in with the hot water in the POU tank as he uses it. Most people have their water heaters set high enough that they have to blend some cold in with the hot for their showers anyway, so the usage from the POU heater will be slow enough that the incoming slug of room-temperature water from the main water heater shouldn’t draw down the temperature of the POU heater much.

That's what I was trying to confirm. However, I'm not hearing a lot of love for POU heaters and I'll consider a recirculating pump. Thanks for all the input.