Replacing and upgrading an old Grunfos hot water circulating pump

[Ben E]

My home has a UP 15-18B5 recirculating pump on domestic hot water. Original to home (2003). Dedicated return line.

Pump chamber is soldered to copper pipes. Annoying -- best practice is flanges -- but I am not the original builder, so this is what I'm working with.

Pump has failed. I need to replace it.

First idea is a direct replacement with same model. Shut off water using valves before and after the pump, disconnect electricity, loosen the four allen screws holding the pump motor onto the chamber, remove and discard current pump motor, install new motor, tighten screws, open valves, reconnect electricity. Workable? Then no need to solder.

Suppose I wanted to substitute a more modern replacement with efficient motor. The Grunfos Alpha and Alpha2 series look promising, and cost difference is not so much. From online photos, the alignment of the four allen screws looks like it could be the same, though I can't tell if the screw placement is really the same, if the seal is the same, if the existing pump chamber could be used with the Alpha/Alpha2 pump motor. Anyone know? Any concern using a stainless steel Alpha pump with the existing brass chamber? Other suggestions for a drop-in replacement?

 

[John Gayewski]

How many feet of pipe is your hot water loop. How long is the trip from the pump and back in other words?

 

[Sponsor]

 

[Ben E]

John, good question. I suppose I don't really know. Don't have plumbing plans. But big house (7200 square feet) Based on location of water heater versus furthest hot water fixture in the system, I'd say it's 100 feet each way, making allowances for turns as well as vertical distance.

The UP 15-18 always performed fine (instant hot throughout the house), so I definitely do not need a bigger or more powerful pump. Quite likely the UP 15-18 is oversized, all the more because I recently insulated all the exposed hot water loop in my crawl space, which previously was largely uninsulated. Part of the appeal of Alpha/Alpha2 is that they could slow the pump rate when appropriate.

 

[John Gayewski]

You have the right size pump according to your footage and manufacturers literature on it. That pump does 3gpm at 200 ft. Your loop doesn't get smaller. I'd rebuild.

 

[Ben E]

John, I read the Grunfos literature about the Alpha pumps. Do you think they'd offer a material savings in electricity? Reducing 85W to (say) 40W, through the more efficient motor -- that's a savings of 45W per hour, times 10 hours of utilization per day, times 10 years service life times $0.12/kwh -- that's $197 less of electricity. I couldn't reach a conclusion whether Alpha has any other benefits -- whether the promised smarts, automatic learning, etc. would be useful to us.

 

[John Gayewski]

I don't see how it would help. In what situation do you think the pump would burn less energy and save you money?

You could put any pump on a timer or remote so it doesn't run all of the time. But mostly the claimed benefits of a vfd would be that it can do the work of several differents pumps within the same pump. Your system doesn't change its need. This particular pump is already sized to give you the correct speed for what you have. What would a different pump be trying to do?

 

[Ben E]

I was thinking that an efficient electric motor, such as a modern ECM motor, uses less electricity than a traditional motor, to do the same work. That's part of what I see in the manufacturer product descriptions. No?

Agree that we can use a timer or remote (and we will).

 

[John Gayewski]

I was thinking that an efficient electric motor, such as a modern ECM motor, uses less electricity than a traditional motor, to do the same work. That's part of what I see in the manufacturer product descriptions. No?

Agree that we can use a timer or remote (and we will).

I know ecm motors are pretty powerful, but using less energy I'm not sure of. If you switched to an ecm motor you could likely get a smaller pump to do the same work, but (I could be mistaken here) watts equals work. You need 3 gpm through a fixed amount of pipe. That means the wattage used will/ should be the same. Your not changing the amount of work your pump is doing. A variable pump can change the amount of work it does. It does this when the length of the loop it's pumping changes (as in a hydronic system). Your loop is constant.

The only problem with a remote or sensor controlling the pump is that the on/off on/off is bad for the pump. So there's a trade off there.

 

[John Gayewski]

If an ecm "gets more to the rear wheels" you could save some energy. It could be that there's some wasted energy in a traditional pump vs an ecm. Such as friction in turning a gear. I could see some savings there.