Would this recirculation idea work ?

Marty_2

I am not a plumber :) The cold incoming water goes past all the supply lines to things then travels to the tankless and back ? If so should work However what about the tempering valve seeing the hot recirculated water on its cold feed ? an indirect or standard water heater I wouldn't worry too much, tankless I would think some about that. a domestic expansion tank might not be a bad idea either if the tempering valve isn't an issue.

Unknown

I've been trying to help my brother in law

with a hot water problem . The boiler and tankless coil are in the garage and the sinks + bath are about 75 running feet away . All the piping connects together in a plumbing wall with all the fixtures and water main within 2 feet of each other . It takes a good minute to 2 minutes to get hot water to the sinks .

There really is no way to run a separate recirc line back to the boiler , so I tried a used Grundfos Instant Hot Water System . There was a big blast of hot water when you open the cold of the sink , then lukewarm water in the cold position , all the time . I didn't have the instructions , got them online tonight . I'm going back tomorrow to test the piece under the sink .

But I want to try something else . The Grndfos circulator is pumping away from the coil out to the hot side of the fixtures . What if I teed the hot pipe coming from the coil into the cold going to the coil , near the fixtures - but before the flow goes to the fixtures . Then I would put a check valve on the cold pipe to the coil - after the tee near the sinks . I'm thinking it would stop any hot water that was recirculated in the cold pipe from mingling with the cold water going to the sinks . There'd be a little hot water when a sink is first open , but not the steady warm water he has with the Grundfos right now .

I tried to use Microsoft Paint to show a little better what I was describing , but I can't get the knack of it . I'll try to write it out and scan it into the computer . Thanks for any help .

Unknown

Yes

the last pipe the incoming cold from the street goes to is the inlet to the coil . The first thing the hot from the coil would go to is a tee - one end of the tee connects to the coil cold with a check valve , and the other end of the tee goes to all the hot faucets . All these connections would be very close together in a plumbing wall .

I don't think the tempering valve would be an issue . I'm just circlng already tempered water , I think the valve would react fine . That's just a guess though . Thanks alot Marty .

jerry scharf_2

what I would expect

Ron,

Without a separate recirc line, you are pushing the hot water back down the cold line. That's going to make not very cold water. I don't think there's much you can do with a recirc system that's plumbed as described. I don't think check valves would work.

The Taco d'mand system only runs when you tell it to and shuts off when it senses hot water. It uses a small pump because it's designed to go in small applications. If you cobbled together an aquastat, relay and a pump with decent GPM plumbed between the hot and cold water lines with check valves, you should be able to move the water in the lines faster than it can come out the tap. There may be a little flow noise, but it should only last a short time.

Here are some back of the envelope numbers:

75' of 1" copper holds about 3.5 gallons, That will take just under 2 minutes to go through a 2GPM faucet. If you can move 7GPM, you get it down to 30 s. Getting much more flow than this is probably unrealistic.

At 7GPM, the flow is under 4f/s in 1", 6+ f/s in 3/4" and 12f/s in 1/2". So expect some noise in 1/2" at this flow rate.

I waived a dead chicken at a piping estimate and it came back as 200' of 3/4". Siggy's software then says a Taco 0011 would give you just over 7GPM

The easiest way for me to think of controlling this is a bit like a magnetic motor starter. You have a relay who will keep itself closed once energized. A momentary switch (like a door bell switch) would energize the circuit and the pump would continue to run. The aquastat would need to act as a normally closed switch in the coil circuit, so that when temp is reached the coil circuit is broken and the pump stops.

hope this was some help,

jerry

Marty_2

2 check valves

Ron would the piping look anything like this very poor attempt at a drawing ? check valves where the x's are blue for cold red for hot.

kevin coppinger_4

Ron..

can you /could you snake some 3'8" pex from the bath back to the coil? That would keep the hole in the walls to a minimum. If you could that would be most of the battle, I even use that for gravity recir. and it work pretty well....kpc

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