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Installing My Solar 
Domestic Hot Water Heating System

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HOME Receiving

Day 9 - plumbing the pre-heat tank

July 31, 2006. Time Invested:
3:40 Plumbing in the new tank
1:00 Finding the leaky pressure relief valve and cleaning up

August 1, 2006. Time invested:
1:00 Get replacement valve and installing it

NOTE in 2010 we replaced the tank heater with a Rinnai tankless model

I really should have started in the day time so I could have made a run to the hardware store if I needed something.  Murphy rules when you are plumbing...  I started at 8:00pm.

It was pretty easy to get the pre-heat tank in place, it sits right up against the propane fired water heater.  I set it on some lengths of treated 2X4s to keep it off the damp cement floor.

I used the revised layout that I got from Butler Sun Solutions that shows how to plumb in a solar pre-heat tank.  I began by shutting off the water main and draining the plumbing from the bottom of the hot water heater.  Oh, yes, before that I had shut off the gas and power to the water heater and I took a long shower to cool off the tank.  I attached a garden hose to the heater tank drain, and ran it outside.

Note the unusual connections to this tank.  I accidentally bought an electric water heater designed for mobile homes.  It has connections on the side as well as the top, and no dip tube for the cold inlet at the top, so I had to use the lower inlet on the side for the cold feed.

It wasn't too hard to plumb in the cold line.  There need to be 3 shut off valves so that the tanks can be configured as a normal hot water heater, or fed through the pre-heat tank.  The pre-heat tank also needs its own shut-off.

I moved on to plumbing the wand outlet into the cold side of the propane tank using a T that allows that original water heater to be fed from cold, or solar heated water.

Then I plumbed in the tempering valve on the hot outlet of the water heater (upper left in the image at right).  It is hidden by the white combustion exhaust pipe at the upper left of the image to the right.   3.5 hours - not bad!

Then the trouble began.  I turned on the cold main and filled each tank -- watching for leaks.  I stopped twice to tighten unions and swage fittings.  Once the system was holding pressure I noticed this dripping sound.  "This can't be good" I thought.  Sure enough the over pressure valve next to the main pressure tank had sprung a leak.  (For those without wells, you need a pressure tank to store pressure so the well pump doesn't run every time you run water.)   This little valve had rusted out, and I noticed that the pressure gauge was sticking too.  Darn!  There was a lot of water to mop up -- and more importantly no chance of taking another shower tonight.  Did I mention it has been 85F and humid as a sauna all day?

I had to shut off the main again and attach the garden hose to the inlet drain to relieve the pressure.  Shown below are the new pressure gauge and below it the new pressure relief valve.

  August 1, 2006

After an early morning run to the plumbing supply, I was able to replace the defective relief valve and install a new pressure gauge.  Now I could pressurize the whole house and fire up the water heater.  It's another hot, humid day and much to be done.

I decided to install the thermal cutoff switch next.  According to the well written Installation Manual, this needs to be at the top of the tank and touching the metal of the tank wall.  I opened up the electrical panel at the top of the tank and removed the inner metal wiring box to expose the insulation.  I cut away the wires that feed the electric element -- I won't be needing those!  Then I cut out a square of insulation for the thermal switch so it could fit down against the tank wall.

I pulled the wire out through the electrical fitting and secured the wire.  This is a great spot for this important switch.  If the tank gets over heated from a really good solar day, this switch turns off the collector circulation pump so no more heat can be added.

In 2010 the propane water heater tank failed and we replaced it with a Rinnai tankless on-demand propane fired unit.  You can learn more about this heater and it's installation here.  The Solar Wand remains in the solar storage tank on the right.

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