New house with Recir. pump

[Wildduk]

I just bought a new house that has a Rinnai gas water heater and a small 10 gallon elect. heater. The electric heater has a pump with a timer on it.....Should I run the pump just during the day, or leave it on all the time......I know I could turn it off at night, but when it comes on in the morning it seems it would take a while to pump and heat all the lines up again.....Not sure which option would save energy

Thanks

 

[havasu]

I have my recirc pump set to come on at 6:15 AM for my morning shower at 6:30 AM, and at 11 PM to have instant hot water to wash my face before bed. I figured twice a day was minimal power consumption, which solves my many wasted gallons of cold water waiting for hot water. Since my local water company just sent me a notice that they were increasing rates 30% immediately, I may have to adjust this.

 

[plumbernyc]

Just set the timer properly. Which pump model do you have?

 

[Wildduk]

it is a Grundfos pump, not sure of the size right now....the issue is that I need to set the timer to come on at 4 o'clock to get instant hot water at 615.....Just seems a litle to early to need to set it to come on....

 

[havasu]

Sounds like your system is way underpowered, or something is wrong with it.

 

[Mr_David]

You really don't need to move the water very fast. if the pump is over sized it could wear out the inside of your recirc line prematurely.
Well that is if it's a copper system.
I don't have 1st hand knowledge of plastic/pex hot water systems.
If you can, flush the return line. It can possibly have some air trapped in it.
It shouldn't take but a few minutes to get the line hot.

Question
Is the pump mounted on the outlet line of the heater or
does it have it's own designated return line that brings the hot water back to the heater?

 

[Wildduk]

I looked up the model and its 1/25th h.p.

The hot water comes out of the rinnai, through the elec. heater, makes a loop throught the house, then enters the hot water line again before the elec. water heater. Its got check valves right after the rinnai and right after the pump.....

Is there any way to tell if the pump is operating properly.....

Thanks

 

[Mr_David]

What's the Model #
Did they install a hose bib and/or any valves so you can periodicaly flush any air out.
Can you take a picture or 2 and post them. It would help
The pump can get air locked if not properly installed.
They are designed to cup and move the water.
If air gets trapped in them they can't move the water

 

[Wildduk]

The model number is UP15-18B7.

The instant hot water works during the day when the pump is on. i just am trying to utilize the timer and shut it iff at night. There is a hose bib and I've used it to get hot water, so i'm thinking there is no air in there, but I could be wrong....

 

[Mr_David]

I don't have any data but that pump is okay and not to big.
It is our most commonly used size of pump.
Past experience your pump is install in such a way that as I mention before can trap air.
Have a valve installed between the recirc line check valve and Tee and a drain cock/hose bib just after the pump.
Attach a hose to the drain cock , close the new valve and flush the return line.
The pump is also trying to move water through a spring loaded check valve.
These pumps from my understanding cup and move the water. So although it is a light spring it can reduce the water flow a little.
In the picture I see a little yellow cylinder hanging under the timer .
This looks like the capacitor for the motor and should be inside the housing where the electrical connections are made.

The best way to install the pump is to extend the return line down , install the pump on a horizontal line level or below the connection to the supply going to the water heater. This allows the trapped air to naturally percolate out of the pump back into the system, eventually expelled out through the fixtures

 

[Wildduk]

I was messing with my system today....I shut the pump off for most of the day and let all the lines cool down.....I then turned on the pump to see how long it took to get hot water. I did get hot water fairly quickly, but it then cooled a bit. I then left the hot water running and went to the basement to look....

It would seem what is happening is when the pump comes on, it initially circulates the hot water from the tank thru the loop....The initial water temp is fairly hot. Since the loop is cold, it in turn somewhat cools the water, then it makes its way back to the tank......

When I turned on the hot water, the Rinnai did kick in, but when feeling the pipes, the one coming out of the Rinnai was very hot, but the one coming out of the elec. tank was luke warm, because it was mixing with the water that was somewhat cooled from the recirc. pump coming back on.

I know that Rinnai recommends a 2-5 gallon tank when using a recirc. system. Could it be that 10 gallons is actually to big....

i'm not a plumber so I could be totally wrong here, but it is just my observation.....

Maybe big is not better in this case with the elec. water heater...

Duk.