connecting an indirect and an lp water heater together

jrv8984

So, I have a 70 gallon Vaughn indirect that is connected to my coal boiler this supplies my DHW in the winter. I have a LP water heater that I use in the summer. I need to get my water temperature down to 120 degrees as a requirement to be a Foster parent. I picked up a Caleffi tank mixing valve to take care of this.


Ok so I need to move the LP water heater (for more than just the convenience of plumbing together, the previous owner installed it with about a 10' horizontal run of vent pipe into the outside basement stair well) next to the indirect water heater, and plumb them to share the mixing valve. This in and of itself isn't a problem, but I was wondering if there was a way to plumb the 2 tanks together so that they feed each other. So in the winter the coal boiler would heat the indirect which would then flow into the LP water tank, and then in the summer the hot water from the LP tank would flow into the indirect tank, thus giving me a larger capacity of hot water, and preventing stagnation of the water in the tanks while one of them is not in use during summer or winter.

I had considered swapping out the LP unit to a heat pump unit, but all of them are to tall (only 58.5" of height) to fit in the basement where it needs to go (250 yr old stone farmhouse)

Thoughts?

GroundUp

But do you need more capacity? Sounds like a huge waste of fuel to keep 120? gallons of water hot instead of 70 or 50 or whatever your LP unit holds. For them to feed each other it'd be as simple as a bronze or SS recirc between them but I don't see the logic unless you have 13 people in the house and actually need that much hot water at one time

hot_rod

Do you always want to run the LP? If so, a simple way would be to pipe them in series, feed the indirect first to the LP and then the mixer.

The indirect will do some pre-heat even unfired.

If you want to switch back to the indirect only in winter some manual valves and piping would be a way to isolate the tanks.

HVACNUT

Is this a historical home or a home that must maintain its originality?
How about ditch the coal and install a mod con or a high efficiency oil fired boiler with the Vaugn tank.
Do you also need an anti scald solenoid valve in case the mixing valve fails?
I know, I know, $%☆¿!* tree hugger.

hot_rod

HVACNUT said:

Is this a historical home or a home that must maintain its originality?

How about ditch the coal and install a mod con or a high efficiency oil fired boiler with the Vaugn tank.

Do you also need an anti scald solenoid valve in case the mixing valve fails?

I know, I know, $%☆¿!* tree hugger.

Are the anti scald solenoid valves, with thermostatic mix valves being mandated by AHJ or inspectors? I have heard this requirement a few times now? The ASSE 1070 listed valve should be adequate for scald protection?

jrv8984

lp unit is only 30 gallons

jrv8984

They have to physically measure the water temperature at all the fixtures inside the house.
Its and old stone house, possibly the 1st one in the county, I am working to restore it.
No way using oil is going to be cheaper than Anthracite coal @ $170 ton
Used 10 tons of coal last year to heat house and part of the garage, should be less this year with the work that has been done to the house, but we are very warm and happy all winter.
We never run out of hot water in the winter, but always do in the summer with the LP water heater.

HVACNUT

@hot_rod
I dont know the code but some of the group homes for the disabled I've done work in required a domestic hot positive shut off solenoid controlled by an aquastat at the mix. And max temp at the mix was 105°.

jrv8984

Venting is an issue because of height and basement window access. I'm thinking that plumbing a tankless condensing LP water heater into the indirect is the way to go. Then just turn it off and close the valve for it in the winter.