Recirculation Pump Installation Questions

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Wren

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I'm curious about the best way to install the Grundfos pump that I bought. The outlet of the pump is a 3/4" union fitting while the input has a 3/4" sweat connection.
I'm planning on having the return go back into the water heater through the drain on the bottom after adding a tee and reinstalling the drain bib.
It appears that these pumps are often mounted directly to the water heater output with a union to 3/4" pipe connection, but I couldn't find a pump that was for sale that was configured in that manner, so I'll have to find a sweat to female NPT to thread it onto the WH outlet. Also, I've read that it's better to have the pump at the water heater near the return inlet, but as I mentioned above, I've also seen it mounted directly to the WH on the output nipple.

The pump doesn't have any mounting provisions that I can see so I'm thinking that it should be mounted directly on top of the outlet nipple. I believe that I have enough headroom to do this, but I'll have to mock it up to know for sure. It's going in a crawlspace.

In the photo, one can see that the input (lower inlet) is a sweat connection while the upper is a 3/4" union.

I've also seen these pumps mounted on a tee that's added to the drain nipple, but it seems like it would be easier to put it on the WH output if I can. I'm not certain about how to secure the PEX pipe I'm using against the side of the WH for the return if I put it low on the WH at the level of the drain.

I hope all of this makes sense. Any advice would be appreciated. Thanks!

Pump.jpg
 

John Gayewski

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The only reason to buy a pump with those connections built in is if you need/ want those connections. You have a dedicated recirculating line?

If so sweat a piece of pipe to the inlet. Then thread a piece of pipe to the outlet. Then mount those pieces of pipe to a wall or beam or whatever. Then hook the pex to your attached piping.
 

Wren

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The only reason to buy a pump with those connections built in is if you need/ want those connections. You have a dedicated recirculating line?

If so sweat a piece of pipe to the inlet. Then thread a piece of pipe to the outlet. Then mount those pieces of pipe to a wall or beam or whatever. Then hook the pex to your attached piping.
Yes, I have a dedicated return line that I'm installing.
Any comment regarding if it's best to put the pump on the outlet of the WH or to put it on the return side close to the drain bib?
 

left_behind

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IMHO:
six of one, half dozen of the other. i've seen it done both ways. the main consideration would be an electrical outlet and ease of application and space. sometimes you just don't have the space at the bottom in a water heater enclosure.

as for the union x sweat, Ugh! as a retired C-36, i've ALWAYS kept whatever i installed "Modular". even if the part was meant for the long haul! inevitably "I" was always the guy going back, and would smile when i had to rebuild or replace.

that being said, i would add a FIP (or MIP) x Copper Brass Union to the sweat side of the pump.
don't forget the proper ball valve(s) to isolate said recirc pump, and necessary check valve as well. you'll thank me if/when that time for repairs happen.

Screenshot 2022-03-29 220939.png
 

Wren

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Thanks very much for the reply. I wasn't sure of the nomenclature for what I needed to buy.

Are there any pitfalls to watch out for when sweating a fitting to the pump? Should I remove the impeller assembly, etc. or fill the pump with water so it doesn't get overheated? I've sweated plenty of ball valves, and other fittings, but never a pump. I don't want to cook it of course.
 

John Gayewski

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I prefer to have the pump on the return and pumping back into the heater.

Different pumps are made differently. If there is a rubber seal between the pump body and the motor housing then yes I'd take it apart. The size of the pump also plays a part. If you think the rubber seal will get too hot then yes take it apart. If the fitting cup is really far away from any rubber and not too thick you could probably leave everything on it.
 

Wren

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I think what I'll do is fill it with water and set it up so that the output that I'm soldering to is on the top. If I work quickly, I think I'll be OK.
 

left_behind

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as stated above, just be sure you have the pump sized correctly for your application!
too aggressive will burn out your copper fittings and cause pinholes. i used to put 'em on a timer. too small and it just won't give you the desired effect. i've seen some applications where gravity actually worked recirculating hot water! rare, but it's out there!
 

Wren

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Any tips as to the best solder and approach to use regarding sweating a piece of 3/4" pipe to the inlet of the pump? I'm a certified weldor, but whenever I have to solder plumbing pipes, I get nervous.
 

John Gayewski

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Any tips as to the best solder and approach to use regarding sweating a piece of 3/4" pipe to the inlet of the pump? I'm a certified weldor, but whenever I have to solder plumbing pipes, I get nervous.
I like bridget it's one of the lower temp solders. Use the green label tinning flux
 
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