If you don't want buttons but still want it to be as efficient as possible you can put a flow switch in the hot water supply line that your HA system uses to start the pump. Of course if the pump is running the flow will never go to zero so you will need to turn off the pump after some time delay, say 30 seconds.
Different Water Heater Recirculation Methods
- Thread starter jmed999
- Start date
Desert_AIP
Senior Member
If you don't run the pump prior to demand, i.e. wait for the flow sensor, then you are really defeating the purpose of the recirc system - instant hot water.
The flow sensor could work in conjunction with a timer.
Run the pump just prior to the high demand times via a timer, when you shower in the AM or PM for instance, and use the flow sensor for the remainder of the time.
You can run the pump for just a few minutes which will cycle hot water into the pipes and cooler water back into the heater input.
This will prime the system enough so you don't have to run the pump continuously.
The water in the pipes, if insulated, will stay warm for quite some time.
The flow sensor could work in conjunction with a timer.
Run the pump just prior to the high demand times via a timer, when you shower in the AM or PM for instance, and use the flow sensor for the remainder of the time.
You can run the pump for just a few minutes which will cycle hot water into the pipes and cooler water back into the heater input.
This will prime the system enough so you don't have to run the pump continuously.
The water in the pipes, if insulated, will stay warm for quite some time.
Not completely. The water velocity will be much higher with the pump running so the time to get hot water to the faucet will be significantly reduced, especially with low flow faucets.Desert_AIP said:
It would be helpful say in the middle of the nigh when someone has to use the bathroom but is outside the normal time period you have the pump set to run.
You could also use a motion detector in every bathroom/sink for the same purpose.
jmed999
Active Member
Lots of motion sensors around the house can get ugly. At first I think I'll just use home away and between 12AM and 5AM = off. Of course I would also use an auqastat. I don't think this would increase my gas bill much at all. If it does then I could fine tune the automation.
The recirced water has to be reheated to prevent cold "flashes" at the outlets. So the electric heater should be of proper capacity to be able to handle all volume of cold water initially in the pipes. We have a large water storage tank that accepts recirc water, so it's not an issue, otherwise it is similar to method 3, except it uses solar instead of electric. I use temperature sensor at the end of the hot water pipe, the pump will shut off when a set temperature is reached. It is glued to the pipe, but if I did it over again, I would install an in-line sensor. We control the pump both via HA and from buttons at each water outlet, so the run time will be different depending on the location of the outlet, and the water does not always have to reach the end point. Most of the time the pump is not running, and this saves resources. You could also use motion sensors near the fixtures to automate the pump.
Desert_AIP
Senior Member
If the pump switches on after the faucet is opened, then the initial flow out of the faucet will be the cooled water in the pipe.Automate said:
Agree The hot water will arrive more quickly than it would without the pump, but it would not be instant.
And with the faucet open I think a lot of the water will be pushed out rather than recirculated.
You are right, it would not be instant. Like most everything in life this is a trade off with no clear "right" answer. It really depends on what the OP is trying to achieve. If they never want to wait for hot water they need a constant recirc system.
One thing to consider is the size of the pipes. I have oversize pipes to feed multiple heads in the shower and a 1/2" return line and a fairly low flow pump. That's part of the reason for the delay but I am fine with that. A bigger return line, smaller feed line, or bigger pump would all reduce the delay. For constant circ only a very small pump is needed.
The pump pulls water from the faucet area and pushes it back to the heater. It won't cause more water to be pushed out an open faucet. If anything it would be a bit less because it lowers the pressure but I doubt the pumps effect on faucet output would be much. The water recirculated will be almost unchanged.
One thing to consider is the size of the pipes. I have oversize pipes to feed multiple heads in the shower and a 1/2" return line and a fairly low flow pump. That's part of the reason for the delay but I am fine with that. A bigger return line, smaller feed line, or bigger pump would all reduce the delay. For constant circ only a very small pump is needed.
The pump pulls water from the faucet area and pushes it back to the heater. It won't cause more water to be pushed out an open faucet. If anything it would be a bit less because it lowers the pressure but I doubt the pumps effect on faucet output would be much. The water recirculated will be almost unchanged.
Either way, if you haven't run the circ pump in a while you are not going to have "instant" hot water. You could use the flow switch like a push button. Turn the hot water on and then off right away. This will be enough to trigger the flow switch and start the pump. After waiting 30 seconds or so with the water off you turn it on again and have hot water. You will have to wait a little longer this way because you are not combining the pump flow with the drain flow to get the hot water to the faucet quicker. The advantage to this way is you are not wasting water down the drain. You also don't need to worry about mounting an unsightly button or instructing house guests how to use it.Desert_AIP said:
JimS said:
Good point about the pump size. Some systems are designed with a small pump that runs continuously other systems with a larger pump that cycles on and off. With a tankless hot water heater you probably are not going to want a continuous pump but still need a small tank to eliminate the "cold water sandwich effect". This has a good explanation of what causes the sandwich and some cautions with circ pumps with tankless http://www.profitableplumbing.com/tankless101.html Search down to "Cold water Sandwiches"
Rinnai's solution is here http://www.tractorbynet.com/forums/attachments/related-topics/61100d1158263375-tankless-water-heater-code-question-cold_water_sandwich.pdf
jmed999
Active Member
Automate said:
Thanks for the links! The 1st one was very informative! The 2nd link was a link I have already posted here in this thread but thanks anyways!
I called Noritz yesterday and they recommended Method #2 (using a storage tank) but they said I could use Method #3 (using an electric tank). Your first link recommends Method #3. I must say the lady I spoke to at Noritz didn't seem very knowledgeable in her answers so I'm reluctant to just take her word and run with it.
drozwood90
Senior Member
I know with my last house, I put in a tankless unit. The manual specifically forbit the use of a recirc. pump.
Check your manual.
--Dan
Check your manual.
--Dan
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