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Discussion Starter #1
I would like to have instant hot water at every faucet in my place. The problem is that it takes a while and wastes a lot of water to get the hot water to flow.

Currently, I have a large electric tank heater but it's upstairs a long way from my kitchen, for example.

I would like to install a small electric on-demand hot water heater under the sink so I can instantly get hot water. It doesn't have to be scalding, but hot enough you can wash your hands. However, I want the water supply for the electric instant hot water unit to get it's source water from the standard hot water supply line so that when the real hot water arrives, finally, it shuts itself off and lets the hot water from the tank flow through.

I do not have gas, only electric. I have not made any purchases and thought I would ask here before I go working on an Arduino and an electronic water valve to Do It mYself.

I have worked on a friend's plumbing with the recirculating hot water solution and it sucks, sucks, sucks. In fact, we have had more than a half dozen plumbers over to make the system work and it's a nightmare. I doubt I want to deal with recirculating the hot water. But I am open to discuss it

Thanks in advance.
 

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Discussion Starter #3
Yes and no. First, thanks for the reply.

THe way these hot water heaters work, I believe, is that they go on the cold water supply line. They wait for someone to open a tap and the flow of water triggers a relay that starts up the heater. It runs off and on while the water is flowing and then shuts off when the water stops.

I want a device that connects to the HOT water instead. When the tap is opened, it meausres the temperature of the incoming water and if it's hot enough, it doesn't kick the heater part on. It just lets the water flow through. When the water gets cold or if it starts out cold, the electric mini heater kicks on and takes over until the source water is hot again or the tap is closed.

Ideally, this would be seamless and the person at the faucet would have no idea it was happening. I won't hold my breath on that.

I can probably make one myself with an electronic thermometer, an arduino and a relay. The problem is that if the electric water heater is off, I need to be able to flow the water through it regardless. (I guess this should work because you get water if the power goes out).

Now one last thing: If this kind of unit doesn't exist and someone here with connections starts making these, please be kind and count me in. LOL I would hate to have someone steal my idea, get rich and leave me hanging.

Thanks again for the reply.
 

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retired framer
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Yes and no. First, thanks for the reply.

THe way these hot water heaters work, I believe, is that they go on the cold water supply line. They wait for someone to open a tap and the flow of water triggers a relay that starts up the heater. It runs off and on while the water is flowing and then shuts off when the water stops.

I want a device that connects to the HOT water instead. When the tap is opened, it meausres the temperature of the incoming water and if it's hot enough, it doesn't kick the heater part on. It just lets the water flow through. When the water gets cold or if it starts out cold, the electric mini heater kicks on and takes over until the source water is hot again or the tap is closed.

Ideally, this would be seamless and the person at the faucet would have no idea it was happening. I won't hold my breath on that.

I can probably make one myself with an electronic thermometer, an arduino and a relay. The problem is that if the electric water heater is off, I need to be able to flow the water through it regardless. (I guess this should work because you get water if the power goes out).

Now one last thing: If this kind of unit doesn't exist and someone here with connections starts making these, please be kind and count me in. LOL I would hate to have someone steal my idea, get rich and leave me hanging.

Thanks again for the reply.
I think those are made for your tea or instant coffee and yes on the cold water line. I was thinking it could be adapted.

A few years ago there was a circulating system that was just a pump under the sink and it would pump hot into the cold line until heat was detected so the controller is already been invented and could be used to turn the heater off and back on as the water in the line cools.
 

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If it's just for this one kitchen sink, install your little heater and supply it with cold water and forget about main water heater. There is no advantage to using water from the big tank if the little one is able to keep up. Both heaters should use the same amount of electricity in the grand scheme of things. The only advantage to keeping the main water heater hooked up to that sink would be redundancy, which you could achieve with some manually operated shut-off valves.
 

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Our instant water heater has an adjustable outgoing water temperature setting that modulates the heating element. If water arriving at the instant heater is at or above the output temp, it shouldn’t heat.
 
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Did your friends recirculation system use modern tech. With thermostatic controlled balancing valves?
Most idiots try to do it with a ball valve. Don't even use a balancing valve.
 

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If you draw the hot water through a pipe the diameter of a soda straw such as what an office water cooler delivers, then an under-sink tankless water heater wilil draw just a modest amount of electricity, say, 5 amps on the spot. If you draw the hot water through an ordinary sink faucet with aerator, etc., the under sink heater will probably require in excess of 30 amps.

An under-sink tank type water heater would need at least three gallons of capacity so the cold water in a static (non-circulating) long run from the main water heater in the basement won't drop the hot water temperature at the faucet too far as it commingles with the tank contents and before new hot water arrives.
 
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