Hot Diggity – Hot Water Recirculation Line

The punch-list to the drywall stage is thinning out.  The other night I installed the recirculation line for our DHW (Domestic Hot Water) line.  The purpose of this line is to provide nearly instantaneous hot water at any of the fixtures throughout the house.

The line itself is a ½”diameter PEX tube that provides a return path for water to the hot water tank.  A pump near the tank keeps water flowing in a loop - from the tank, through the main DHW line, and back again via the recirculation line.  The pump is a Grundfos model that runs silently and at very low power consumption.  I’m told it will cost us about $10 a year to run the pump, which includes a timer function so that water needn’t circulate while everyone is sleeping.  Here's what it looks like:

I’m not a big fan of plumbing work.  Mostly I despise the multiple trips to the hardware store for fittings.  That said, our water distribution system is mostly PEX tubing, and has special brass fittings which I can only get from one place in Seattle.  In a word, inconvenient if you don’t plan ahead.  For this project, I sent Trissa (who is on vacation and is otherwise spending her days lounging around dreaming sweet things about me...) to the supplier in advance, with a list of fittings to procure.

It only took about 2 hours to run the line from the recirculation stub-out in the basement (left by our boiler installer last summer) to the furthest point in our DHW line, which is the upstairs bath.  At that point I spliced in a T fitting to complete the loop.

Read my post on how easy it is to use PEX.

Aside from the need to find a plumbing supplier for PEX and PEX fittings (not to mention the tools to crimp them), PEX is wonderful stuff.  Someone could make a mint if they introduced a consumer-grade PEX line to the great Home Deposit.  Just imagine if Joe Homeowner could reconfigure his bathroom simply by crimping fittings onto plastic tubing.  No more amateur-looking copper sweats.

Now, I should mention the caveat to this whole project.  The caveat is that the recirculation system didn’t work – at all – when we turned on the pump.  Nothing, nada.  Cold water for 30 seconds in the upstairs bath when we turned on the hot.  That’s about the performance we were getting without the pump.

I kinda thought this would happen.  The system works by recirculating the water back through the hot water tank.  I noticed that the installer had made a small error and had piped the return line back into the outgoing hot water instead of the tank’s incoming cold water.  I emailed Paul at Advanced Radiant and he sent Kelly over to take a look-see.  Kelly confirmed that sure enough it was mis-piped.  45 minutes later he had the problem corrected, and we now have instant hot at all of our taps.  Thanks guys!

Last thing to note.  You don’t NEED a special recirculation line to get recirculated hot water in your existing “traditional” system.  Some ingenious person figured out a way to introduce a special valve (usually under a sink) that uses the cold water line as a return line to the boiler.  When cold water is asked for the valve senses this and reverts the cold water line to its original use.  Pretty cool, although I haven’t tried one in person.   Read about this system here – it’s relatively inexpensive.