Re: Need info on how to hook up domestic hot water to a boiler coil
Posted by allen on March 09, 2002 at 23:37:53:
In response to Re: Need info on how to hook up domestic hot water to a boiler coil
If you are going through this I would just go with an indirect water heater as it uses a zone off the boiler. It is still a lot of work but I now have 7 of these systems now. Personally I love "Super Stores". They come with the thermistat are really well insulated. Maybe 600 for all materials plus mixing valve.

I will try this - but I hope that someone else reads it to make sure that they agree.

Pictures would be nice.

I am not an engineer but I had a similar system that I ripped out this past summer.

There are some copper T's that you will need and I call them T1 & T2 so you don't get mixed up.

Add a one way check valve or backflow preventer in cold water supply then a T1 and then run it to the tankless coil input. We will address the other side of the T1 below.

Next its the hot water from tankless coil, then a taco 008 which is the stainless pump ~100 dollars as this is in your domestic water, then to the cold side of water heater. (I would place the circ pump on hotter side so it is not possible to get air bound.) I would have one of those safety valves should the tank collapse and I cannot remember the name.

Now on output side of water heater (hot) a T2 (Copper T) and on to the the "cold" tankless. All of this sets up a loop to heat the water. The water heater is a storage tank. BTW - there are storage tanks made to do this instead of using a hot water heater.

Now from the T2 which is hot water output to the hot input of the mixing valve. Connect the street cold to the cold input of mixing valve, and then the hot output of mixing valve to the house hot water. Adding a shutoff to house above is a good idea if you have to work on it later! Full port ball valve with bleed down is best.

I would make sure that there is a new P & T safety valve also with discharge about 6 inches off the floor. This is an important safety device.

Electrical: Disconnect a.c. to water heater. Make sure you turn of power first and meter the a.c. to avoid a shock. Now there is a thermistat on the water heater that you have to get to. You are going to have to get a "pony relay" with 2 sets of contacts from plumbing or electrical supply house. When the thermistat calls (closes) it will close T T (thermistat) on the relay. You will have to power 115 volts on the relay as one output will run the circulator pump to pull the water through the water heater. This is where you will adjust either it at 120 degrees; and if higher add the mixing valve. You might not need a mixing valve if left at 120 degrees but I imagine this will be code soon in all states.

Next is the boiler on all year long at > 130? If the boiler cycles on the heating system then the new relay's second set of contacts will have to also pull in the boiler. This is just closing contacts and not supplying power.


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