Point of Use Hot Water Heater Questions

[Alan Rutherford]

Why not run hot water from the main water heater into the POU water heater. You should have hot water from the main water heater before the PUO water heater is out of water.

That's what I'm considering. Trying to find out if it would work as well as I hope it would.

[Bill George]

That's what I'm considering. Trying to find out if it would work as well as I hope it would.

I had assumed that was going to be the case. Why on earth would you try to heat water from the cold water line when there is a hot water line already there?

[Edward Weber]

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

[Alan Rutherford]

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

Maybe I should consider using a recirc pump vs. the POU heater, but I'm not there yet. I'd think the recirculating system could not fail to deliver the hot water. My concerns would be that either I have to run a return line or I return through the cold water line. If I do that, there will be times the cold water is much warmer than expected and that's a problem. If the system includes the kitchen it would also mean sometimes drinking water that has been through the hot water heater, which is not appealing.

The only complaints I can find online about the POU heater are possible short life of the system, which worries me. I can't find any indication of whether you have reasonably constant water temperature as you use the water in the POU tank and it is replaced first by cooler water from the hot water pipes and then hotter water fresh from the central HWH.

[Bill George]

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

[Paul F Franklin]

So 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 recirc setups will do what you want, but they have downsides too. If you don't run a return line, you'll have hot/warmish water from the cold faucet for a while when first turned on. And those systems do waste energy because you will end up heating more water than you would otherwise. This can be minimized by using a pushbutton to activate them rather than letting them run 24/7 or putting them on a timer. But then you have to wait a bit after pushing the button before the hot water arrives. But at least the water isn't just running down the drain while you are waiting. And face it, most time you have a minute or two in the lav before you are ready to shower or wash your hands.

[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.

[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.

[Brian Elfert]

I have read stories of people who had their cost to heat water skyrocket when they put in a recirculating pump. The pipes will tend to radiate some of the heat from the water as it circulates so the water heater has to heat more often. A common thing is to put a timer on the pump to run only during times of day when hot water is commonly used. I don't know how common it is to have bills increase when recirculation is added.

[Bill George]

I have read stories of people who had their cost to heat water skyrocket when they put in a recirculating pump. The pipes will tend to radiate some of the heat from the water as it circulates so the water heater has to heat more often. A common thing is to put a timer on the pump to run only during times of day when hot water is commonly used. I don't know how common it is to have bills increase when recirculation is added.

Not if you do the correct way, Insulate the pipes.

[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.

[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.