Per the attached picture, I'm going to install a Grundfos comfort pump next to the solar hot water system. Supposedly it's half price on amazon, and it gets pretty good reviews.

My question is whether the Grudfos should be connected before or after the thermostatic mixing valve (which works great).

Also, given the tight spacing, any tips on the most efficient course of action in terms of cutting, elbows, etc.?

At the bottom is screen capture of the Grundfos Manual

Solar System 1, Dual Tanks

Solar System 2, Single Tank

enter image description here

  • How is this going to be a recirculating system? And as for the question about before or after the tempering valve usually most tempering valves specify a maximum pressure difference on the inlets eg hot and cold so after the valve.
    – UNECS
    Oct 6, 2012 at 6:25
  • @UNECS, the pump will pull water from the hot line back to the tank through a special tee fitting that bridges the hot and cold lines on the furthest fixture.
    – pdd
    Oct 7, 2012 at 18:54

2 Answers 2


I believe that Grundfos comfort system is comprised of two parts:

  1. The Pump
  2. A special tee fitting

The pump is installed on the outlet of the hot water tank and the special tee fitting is installed on the furthest fixture in the house from the hot water tank. This special fitting bridges the hot and cold water supplies. The basic concept is that when the hot line is not in use, it will cool off. This special tee fitting allows the pump to pull the cooled off water in the hot water line back to the tank through the cold water line. This reduces the amount of wasted water that is poured down drain while waiting for hot water.

In your case, you are going to want to install the pump on the outlet (common port) of the mixing valve. This will allow for the proper loop to be created as well as to maintain the proper pressures on the valve as noted by UNECS.

As for advise on cutting the existing out, you're going to have to remove the entire portion from the wall back to the mixing valve outlet. It also looks like there is not enough room left on the pipe sicking out of the mixing valve to reconnect a new fitting to. You may have to sweat out the pipe and solder in a new piece, but be careful not to overheat the mixing valve as you will damage the internals. If you are going to be soldering the new pipework, keep in mind that the existing fittings that have been used are ProPress fittings which have a rubber seal inside of them (the bump in the hub) and that you need to be careful not to overheat them as well. In both cases you can wrap the fitting or valve with a wet cloth to help keep them cool.


I installed the same mixing valve in my system and have one thing to add to ppd's great response. When you unsolder the common outlet on the mixing valve to add the pump you can remove the internal parts of the mixer if you turn the lower brass section on the top. That way you don't have to worry about overheating the temperature-sensitive parts inside. Also you will probably need the ProPress tool if you are going to put the rest of it back together the same way.

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