Tankless water heater to pre-heat incoming water

Chemist1961

Here's your answer. Look up Powerpipe. It's made about 5 minutes from my house in Waterloo ON and sold through Home Depot, Sears and independents. It uses a 3-4"copper replacement insert up to 7' long for your drain stack with a heat recovery transfer coil wrapped around it. So it is passive but working with demand. When you are showering the first shower drain water preheats the next load of inbound water via the wall of the drain stack before it gets to the heater. I have a 50 US gallon heater and 3 teenage boys. We use low flow, but very good quality shower heads, but the boys sometimes shower for 20 minutes each or more.
So in the morning the total continuous shower time is at least 45 minutes, sometimes with 2 showers running at once. We NEVER run out of hot and there is plenty of pressure in my 35 year old plumbing. Had the system in for 2 years and the gas consumption and water use has dropped. They say it can save between 15 and 50% of your energy cost but hard to peg since I have done a furnace upgrade as well.
To maximize savings I also wrapped my water heater in a insul blanket and wrapped the Power PIPE. This is great permanent solution if you run the shower a lot back to back. Doesn't help as much with a bath tub user or laundry though. The unit is best suited to homes with a traditional tank type heater, electric or gas. I installed my own and did one for my neighbour as well. It comes with 2 Fernco sleeves and I bought Shark Bites just to try. VERY slick install, in a litlle over an hour but I have run a lot of pipe in my time.!!!

AllanJ

Dissect some baseboard forced hot water radiators and use the finned pipe (a couple dozen feet worth) to run the cold water through before reaching the inlet of an ordnary water heater. Mount this zigzag network on the wall, or if there is enough headroom, a few inches below the basement ceiling.

This is a passive system, using the room air to preheat the water.

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The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded.

plummen

Please enlighten me on the issues of preheating water

AllanJ

When the "cold" water enters the water heater at a higher temperature then the water heater does not have to raise the temperature as many degrees and will then bring the tankful of new water to the desired "hot" temperature more quickly.

This means one person can take a shower and it is a shorter wait before the next person can take a shower. But it does not guarantee that the water will stay at a constant temperature longer if people take showers in quick succession; whether it does is unpredictable.

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The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded.

Chemist1961

As stated above, so with the Power pipe the continuous flow of hot down the drain pre-warms the inbound supply to the water heater as long as there is demand at the shower head, and flow down the drain versus a long wait time for a room temp warming reservoir....

plummen

i understand that,im just trying to understand why she thinks its a bad thing for the water heater

Snav

Thermal Expansion - when stringing two heaters together this is a potential hazard.

This is why a 2nd tank near the faucet in question - or a recirc pump is used instead of doubling up the water heaters. If a recirc pump is used it shuts off to prevent hot water from entering the tank.

When people install two heaters for a home there's a proper way of doing it to preven Thermal Expansion from happening.

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Jackofall1

HMMM........I thought that is what expansion tanks are for....yes....no?

The only time you would experience a thermal expansion problem is if you heat the water too much, preheating the water would have no effect. Thermal expansion happens you can't change the physical properties of water, the design a system has to account for this and it really has nothing to do with multiple heaters.

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plummen

So I guess I can take those 3 differant master plumbers licenses and run them through the shredder since ive been doing it wrong for close to 30 years!

Snav

Ah - that makes sense. Thanks.

But yet jackofall make quick time to explain things to me and you did not. Maybe you should consider using all those years of expertise on a DIY forum to kindly educate people when they're wrong instead.

Do you agree with what he said, then?

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plummen

I was waiting for your response,thought maybe I was missing something!

plummen

You could just use a recirc line with a check valve back into the bottem of heater instead of a recirc pump,but thats more for a distance issue waiting for hot water to get to a faucet than a volume of hot water issue.
Doesthat make sense?

Snav

So I take it that you agree with what he said about it?

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plummen

Yes.
Another way is to bring the supply down directly between 2 water heaters and plumb them both with identical length pipes to feed them then tie the outlet side of both together using same length pipes.
This will give you double the hot water over a single unit at any given time if you use a lot of hot water at any given time,but youre also keeping double the water heated all the time which is more expensive compared to just preheating the water to shorten the recovery time in the first set up we talked about