Expansion tank missing help

Grift1124

Hello everyone I’m amazed by the knowledge I can find in this place. I’m now in a predicament where Im seeking advise and direction. I have a Peerless boiler steam boiler with a domestic hot water coil that goes to a HTP model 50 storage tank. To my understanding which took me some time figuring out, was a cold water feed which Tees to the outlet side of a taco circulator that goes to port in storage tank and the other goes to the top side of domestic coil. Out of bottom of the  coil to the other port of storage tank. Then hot water comes out of top. There is an aquastat threaded into flange of coil that’s wired to oil burner and another aquastat in the storage tank tied to the taco relay controller. To my understanding the aquastat in the coil maintains temp in boiler. Where as the one in the storage tank commands circulator to circulate the water from tank back through boiler until satisfied. Does this sound correct? And my series of questions are does the incoming water pressure kind of guide the flow from circulator back through coil? And is there a particular reason the Aquastat on boiler was set to 180degreesF? The boiler would run every hour to maintain temp and my wallet sure loved that. This system has been in place since roughly 2015. The house is newish to me (was my grandfathers) and they had a company come in and put a new boiler in. I just recently trenched and piped for city water. And before I disconnect from well I wanna make sure everything is right. I have had difficulty finding a diagram of my DHW set up and the few diagrams I have found were using the on demand water heater which I figured was close enough (similar concept right?) and they’re all showing thermal expansion tanks and at least a check valve before it on the incoming water. I will attach picture but before I plumb in a check valve and expansion tank I want to make sure Im not causing issues later on. Not particularly understanding why at least an expansion tank wasn’t installed but like I said before, this system has seemed to work great for years. And I didn’t know if it possibly was because the water pressure from the well was so low (30 psi max) that it didn’t pose and issue. Sorry for the long winded explanation. I truly appreciate the help. I’ll be going over to the strictly steam forum for my other long winded questions about the boiler. THANK YOU 

WMno57

Grift1124 said:

Not particularly understanding why at least an expansion tank wasn’t installed but like I said before, this system has seemed to work great for years. And I didn’t know if it possibly was because the water pressure from the well was so low (30 psi max)

Expansion tank not needed when the domestic water comes from a well. Not because of the well pressure. That could have been changed to a 40-60 PressureTrol, and you still would not need an expansion tank for the water heater. The tank for the well is able to accommodate the expansion of heated water.
Now that you are changing to city water, and getting rid of the well tank, you should add an expansion tank in your domestic water system.

Big Ed_4

Your hot water system is call an Aqua Booster . The nonferrous circulator pumps the storage of water though the boiler coil to heat the tank up . A thermal expand tank is needed on closed domestic systems .

bburd

The well tank functions as an expansion tank because it includes an air cushion, provided there is no check valve or backflow preventer between there and the water heater. As cold water expands when heated, the extra volume will simply push back into the well tank.

Newer municipal water services generally have a backflow preventer, so a small expansion tank is needed at the water heater to accommodate the change in volume as the water is heated. Without this, your pressure relief valve will probably weep on every water heating cycle. I have seen this happen.

Grift1124

@WMno57 ok excellent. I will order a tank and fittings. As for a check valve before the tank. Is this necessary? Any diagram I see for aqua boosters as @Big Ed_4 mentioned, either shows one or it doesn’t. I would figure one would be in place to stop circulator flow back through the cold water feed? 

Big Ed_4

There are many ways to pipe in an aqua booster , Some deal with water pressure others deal with keeping the heat exchange clean ...