Proper Backflow For Glycol Boiler

Rizz861

I’ve seen just about every boiler I’ve encountered with the watts 9D backflow and PRV combo on boiler feeds. This includes existing setups that were filled with glycol. I was studying for a plumbing test and in the IPC I came across this : 

608.17.2 Connection to boilers.
”……Where conditioning chemicals are introduced into the system, the potable water connection shall be protected by an air gap or a reduced pressure principle backflow preventer, complying with ASSE 1013, AWWA C511 or CSA B64.4.”

I would think that propylene glycol or ethylene glycol or similar additives would qualify as “conditioning chemicals” according to the code book thus requiring a different backflow than what is normally used on boilers. Am I interpreting this code correct?

hot_rod

it often comes down to the actual l inspector interpretation   RPZ is the higher level of protection

But you may want to consider a fill tank instead. No possibility of dilution, and no yearly inspection fees which BFDs are subject to.

Rizz861

@hot_rod Are you talking about those blue Neptune chemical feeders I see in commercial applications when you say fill tank? 

mattmia2

Propelyene glycol is nontoxic as long as it is formulated with nontoxic additives so if is designed to need a lower level of protection in most hydronic formulations.

Ethylene glycol is very toxic and would require rpz protection.

The feed tanks are usually a large tank with a pump and a prv. One can be made with a well tank or large expansion tank and a prv as well. Axiom is a common brand.

https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon

Rizz861

@mattmia2 What you are saying does make sense, but the verbiage in the code book throws me off. It mentions “conditioning chemicals” specifically. Is glycol a chemical? Yes. Does it condition the water? I’d say yes because it alters water so it doesn’t freeze and changes its heat transfer properties. 

Rizz861

@mattmia2 So it looks like you would fill the system up to whatever static pressure you need and then isolate the ball valve. This fill tank now takes over feeding and maintaining pressure correct?

mattmia2

I'm not sure about the commercial code. It may be all chemicals because distinguishing between toxic and nontoxic is too complicated for the management of commercial systems.

In my reading of the residential code last time I looked at it, it looked like residential chemicals were formulated to be nontoxic and residential hydronic systems were considered low risk so they just required a check valve.

Jamie Hall

Conditioning chemicals are a group of mostly remarkably toxic chemicals used to protect against corrosion and stabilise pH. Neither glycol is, technically, a conditioning chemical. However, as noted, ethylene glycol is very tonic -- even small concentrations can make you very ill, and will kill any pets. Therfore an RPZ backflow preventer isn't an option -- it's required. Propylene glycol isn't toxic, though I wouldn't drink it by the glassful, so can get by with a double check -- unless you are going to include a pH or corrosion control product in the boiler water as well, or it is in the commercial solution you use -- in which case the RPZ is required. The 9D is a dual check.

hot_rod

The Watts 9D is a dual check atmospheric vent, ASSE 1012.

A dual check, non vented would be a ASSE 1024. Different hazard levels of protection.

More and more inspectors are pushing for RPZ, ASSE 1013 worrying about any chemicals that might be added later on. Better safe then sorry. If the building doesn’t have a listed BFD on the main supply,
boiler water could backflow into a public water system.

While the 1013
RPZ is not the highest protection, their listing requires test ports. So it can be tested and recertified In some areas the city or water provider runs the yearly backflow testing program.

States like Florida with so much lawn irrigation you see BFD all over the place as you walk down sidewalks.

I doubt many inspectors fully understand the application for the dozen or so different BFD types and
listings.

The FDA considers propylene GRAS generally regarded as safe, since it is a common food additive
As more chemicals get added it becomes less safe🧐
Some of the high temperature solar glycols did not pass the FDA or NSF testing, too much added inhibitor pushed them off the chart

I wouldn’t drink any fluid, even tap water that spent any time inside a boiler

EBEBRATT-Ed

If you have any type of glycol you cannot use a standard cheap backflow preventer. You have to use what @hot_rod mentioned.

or

have no connection between the glycol system and the potable water. We used to do that and leave a washing machine hose and a boiler drain on the glycol system and one on the potable water so you could add make up water in a pinch. Inspectors have no problem with that

or
have a dedicated glycol MU tank with a pump. Wessels is one MFG

pecmsg

Rizz861 said:

@mattmia2 So it looks like you would fill the system up to whatever static pressure you need and then isolate the ball valve. This fill tank now takes over feeding and maintaining pressure correct?

No

No potable water connection is allowed. You pump from Your tank to the boiler. 

Rizz861

Thanks for the info guys. It sounds like my interpretation of the code is correct and I’ll be sure to keep the suggestions in mind if a customer wants to go glycol or has a glycol setup. Thanks!!