DHW Backflow Preventer

[Dan87]

My oil burner which has a summer-winter hookup is pushing it's DHW to my PEX manifold, which then is traveling through the hot side of the water heater, pushing hot water back out the cold inlet of the water heater, and back into the manifold, thus causing my cold lines at the manifold to get warm/hot. The only cold line that the hot water really travels to next is the boiler cold feed (it's basically creating a loop, and no there is not a recirculater in my system). I've been told I should install a "backflow preventer" on the cold hot water heater feed before the expansion tank (so the expansion tank is in between the back flow preventer and the water heater). That's all well in good, but I've yet to find what I need. I talked to my dad who has done plumbing for 30+ years, and he claims all he has ever used is a spring-loaded check valve in my situation. All of the back flow preventers I'm finding are for boilers and aren't "potable" water rated. Is a spring loaded check valve ok or does a true backflow preventer work better/safer? I feel like what I need is a 3/4" brass or stainless steel, lead free, back flow preventer that is for DHW, but I have yet to find one. If someone knows what I'm looking for, please, let me know! Thanks!

 

[Terry]

You may be thinking of a Reduced Pressure Back Flow Preventer.
Those have a drain on the bottom. It doesn't get better than that.

 

[Sponsor]

 

[Dan87]

You may be thinking of a Reduced Pressure Back Flow Preventer.
Those have a drain on the bottom. It doesn't get better than that.

I ran across these in my research. For my application, what benefit would this have over putting in a simple spring loaded check valve? I'm thinking this is designed to release any excessive pressure build up in case of an emergency, also that it is basically a more advanced design of a simple check valve, but both the boiler and the water heater have expansion tanks to take on the excess pressure in the system, and the water heater obviously has a pressure relief valve. (I'm not really familiar with reduced pressure back flow preventers.) My boiler guy is on me to just have him eliminate the summer winter hook up aspect of my boiler to save me on oil all summer since I now have an electric water heater, but I haven't decided on that as I know that is also a complex debate, which I'm about to ask in the boiler forum; which in and of itself would correct the problem.

 

[Smooky]

If you do it correctly, only cold water will be going through the valve. If there really is no pump you do not want this hot water loop to have to push through a back flow valve. Somewhere above the manifold install the backflow preventer in the cold water line, next will be the expansion tank and past that and before the hot water heater tie in the Boiler Cold return line. A simple lead free spring loaded check valve should work.

 

[Dan87]

I've been meaning to chime back in on this but haven't had time. I went the route of putting in a lead free spring loaded check valve on the cold water supply of the hot water heater, and it worked. However, I since had my local HVAC company out to service my boiler and the technician said I should have no issue simply turning off my boiler outlet to eliminate water flow through it since I have a water heater (I'm wasting oil to heat potable water when I have a 50 gallon water heater that is plenty enough for me). So, at this point I understand that the check valve wasn't necessary if I just would have turned off the boiler outlet. While I understand what he said, I was and still am hesitant to just have water sitting in the potable water coil in the boiler without flowing for an indefinite amount of time, but he assured me this wouldn't be a problem. This technician also said in the summer I can just shut my oil burner completely off since I am in no need of it running with a water heater. I've heard conflicting arguments about this (an oil burner will work leak if the temp is not always warm) and so on, so in that regard I have left it on and maintaining temp all summer to avoid issues, but if anyone has feed back on this, please go ahead, it's an old EFM boiler. While I know a lot of people out there might say that HVAC oil burner technicians just want to sell you equipment and may tell you advice that will shorten the life, especially when it's not theres and very old, I hesitate to think that as this company is a very reputable local business that has an incredible reputation in my area and is insanely reasonable in price. Pic below of finished check valve, thanks for all the input!