Injecting Inhibitor in Hydronic System

Thanks, in advance, for your suggestions!!! I'd like to inject a rust inhibtor in my hyrdonic heating system. I have an MZ Boilder with both baseboard and under-floor PEX heating zones. I'm not sure how to do it myself - any ideas?

If all the air is purged properly from the system, why would you need to add anything anyway? After the water is heated and air purged out, there should not be any dissoolved oxygen in the water to cause any rust. And an auto air vent should get rid of any air from any make up water that gets added in. You asked HOW to add the inhibitor, but I am curious as to why? adding any stuff to the boiler water may somehow get leaked into the domestic water, and that is not a good thing, I believe.

With very few exceptions anytime chemicals are added to a system that is also connected to a potable water system (the make-up water pressure reducing valve on a heating system) it is REQUIRED that a Reduced Pressure Backflow Preventer be installed between the potable and non-potable systems. This is NOT the Watts model 9D that is normally installed.

And, as Bob explained, it is rarely necessary to use chemicals in a residential system. I'll add that unless you want to commit to periodic chemical testing that the use of chemicals is an idea best forgotten.

Thanks! The inhibitor was provided with the boiler - I just never injected it. The boiler manufacturer (Monitor) recommends the additive - it's suppose to help protect the overall system. It's called Bionibal and says it "prevents the formatuation of rust and metal sludge. Prevents algae and bacterial growth. Prevents hydrogenation". The reason this came up is that I just added two new zones and saw the bottle sitting on the shelf. I contacted the company that sold me the boiler and they also recommended I get this stuff in the system. If you all think it's not a good idea...I think I'll forget it, esp if there are no real positives. Thanks again!!

"All-in-one" boiler chemicals are usually about as effective as snake oil is in curing the common cold. The best thing you can do is to make darn sure there are no leaks in your system and THAT will eliminate the incursion of fresh water. It is the fresh water that contains air (oxygen) that is the worst contributor to corrosion *rust) in hot water heating systems. Eliminate the air and you eliminate most of the problems. As for biological contamination...run the system at 180-210 degrees for an hour or two and that will kill any biological contamination.

Furd said:

With very few exceptions anytime chemicals are added to a system that is also connected to a potable water system (the make-up water pressure reducing valve on a heating system) it is REQUIRED that a Reduced Pressure Backflow Preventer be installed between the potable and non-potable systems. This is NOT the Watts model 9D that is normally installed.

And, as Bob explained, it is rarely necessary to use chemicals in a residential system. I'll add that unless you want to commit to periodic chemical testing that the use of chemicals is an idea best forgotten.

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Maybe in Washington but most other places you only need a BFP with intermediate vent like a Watts9D. There are several rust inhibitor products that work well and are recommended especially for steel boilers and low mass condensing units. Getting the chemical into the system requires either a pump capable of overcoming system pressure or you need to take the pressure off the system and again pump it in.

It is very rare to find, or need, anything but potable water in residential boiler systems. If chemicals are added they should be FDA food grade or as was suggested some other form of potable water (feed water) backflow protection is required by the ICC and varies by state plumbing code. An RPZ is nearly always exclusive to commercial applications, but a double-wall heat exchanger is not terribly uncommon.

If you have to ask how to get it in, you probably shouldn't.

Of course, since hydronic systems are closed loop and once filled should remain that way unless there is a leak, the boiler feed valve can be totally removed from the system once it is pressurized. In fact all of the companies that make feed valves tell you to turn the valve to it off after the system has been filled. Lately, because of new code regulations regarding the proper installation of backflow devices with intermediate vents we have not been installing systems with feed valves of any kind. We pump the system full. There is no connection to the potable water supply at all.