Locate Return Recirculating Line

Farmer Dean · 02-19-2009, 10:31 PM

My 10 year old house was built with a dedicated hot water return line for a hot water recirculating system. The timered Grundfos pump is at the 75 gallon water heater. Since the water heater is just about ready to give up the ghost I am replacing it with a tankless. Because of the associated problems with tankless and recirculating, I am abandoning (removing) my my Grundfos and installing a D'mand pump at the master sink (that's the only place the recirc goes). I would like to use the return line instead of the cold line to plumb the D'mand. Where do I look to find the return line to splice into it. I have a slab construction and the copper tubing is in the slab. Would it have been common practice to stub up the two supply lines and the return line all together? In other words if I start tearing out sheetrock under the bathroom sink, is it likely that the hot and return are tee'd right there. I'm not asking for clairvoyance, just your opinion on where to start cutting.

II Weeks · 02-19-2009, 10:54 PM

some recircs use the cold water supply for their return. Do you see 3 pipes under the sink?

Farmer Dean · 02-19-2009, 11:04 PM

I know that my system uses a dedicated return. All I have are the two finished (valved) out supply lines (hot & cold) sticking out of the sheet rock under the sink. Logic would point to stubbing out the third (return) line right next to the hot supply so as to facilitate the finish work. After tee-ing into the hot supply, at that point you could/would 90 out of the wall under the sink to the shut off valve. Once it's sheetrocked you wouldn't see the third (return) line. At least that's how I'd do it, but then I'm not the/a builder. Where should I make the first exploratory cut?

II Weeks · 02-20-2009, 07:13 AM

without seeing it, is there a connection between the two pipes under the sink like pictured below?

If not, then how many pipes are going into and out of the boiler?

Farmer Dean · 02-20-2009, 07:47 AM

Nope, no exposed fittings. The utility room, at the water heater has three lines; cold, hot and hot water return,