honeywell AM series mix valve

tbone52

A couple questions:

I have a Honeywell AM series R model "heating only" valve being used to mix the temp  for my radiant loops. Original system had an external swing type check valve on the mix valves cold input.  I'm doing another system using the same valve type. But I dont understant the check valve need. Do you need to prevent cross-flow ? I don't see anything in the mfg data about this.



2nd question: I'm looking at putting a AM-1 mixing valve on the water heater. For safety reasons. But I'm concerned about reduced water flow. These vales have a CV of 3.9. Any restristions about connecting two of these valves in parallel?

Mark Eatherton

No, and Yes...

No, a check valve is not necessary, even if it were used on a potable water application. and, Yes, no reason you can't parallel two valves. In fact, on commercial jobs, I always parallel two, with proper isolation, so I can rebuild them one at a time without having to completely shut down the system.



I have never understood why people put the check valve on the cold water supply to a mixing valve in a potable water application. Even with a pump on the return, it can't force water into the cold (other than expansion), unless there is a cross connection down stream some place, and if that is the case, the cross connection needs to be found and eliminated any way...



You will be OK.



ME

icesailor

Potable WH mix valves/Checks:

Mark,

I'm not sure if we are thinking of the same situations and the need of check valves on mixers. However, without internal checks or external ones, you get terrible thermal circulation with them. You are supposed to pipe them with a heat trap but not everyone reads the instructions and if you have an indirect with the cold water inlet on the bottom, rather than on the top with a dip tube, where to you put the thermal trap?

Sparco/Honeywell makes one that goes on domestic hot water heaters that screws on to the top outlets with unions and also has a 1/2" recirc port. It has internal checks so that the thermal problem is eliminated.

But, Massachusetts Plumbing Code says that you can not install a check valve on the cold water inlet of a water heater without approval of the Plumbing Inspector. And that you must drill a small hole in the flapper to allow thermal pressure to be relieved. Now, we just install an Extrol tank to deal with expansion.

Thermal circulation burns the thermostatic elements out of those valves unless you do the heat trap thing.

Gordan

The AM-1 I just installed has internal checks on both sides

Since that mounts directly to the hot outlet, no heat trap is required there. I still put in a heat trap on the cold side for two reasons: to stop thermosiphoning from the tank to the cold supply, and indirectly to prevent a possible scalding hazard that could result from that thermosiphoning (where the mixing valve now doesn't have cold water at the cold inlet, but hot water that siphoned up from the tank.)



Not sure how much of a concern that second point is, realistically, but the first one is definitely a concern and the same fix addresses both, so...

Charlie from wmass

on domestic water

In Mass check valves are required as per code to prevent cross contamination of the cold with the hot. In this case if it has functioned well with the check valve I would leave it if it is functioning or replace it if it is not.

Mark Eatherton

Do you guys work in the same State? :-)

Chris says they are NOT allowed, and Charlie says they are REQUIRED?



If they are worried about the POTABLE water cross contaminating, then they'd better start outlawing the WARM setting on automatic clothes washers.



Personally, the only place I put a check valve on DHW system is on the circulation return line and that is to keep the water from back charging to the last fixture on draw and avoid what I refer to as the Roller Coaster temperature condition.



If the manufacturer requires a thermal trap, then it goes in, but I don't think Sparco (Honeywell) requires them and due to the fact that most have a pump on it, it doesn't matter anyway. It IS going to see hot water regardless. Never had a problem with lock up.



YMMV



ME

Charlie from wmass

The under sink recirculation pumps

are also not allowed in Mass. I have been through it with the inspectors who pay attention. They require check valves for any mixing valve that supplies domestic hot water.

Charlie from wmass

Chris is correct

about check valves on inlets to hot water heaters. I am speaking of the check valves at the outlet of the hot water heater and the inlet of the mixing valve. If a check valve is installed a properly sized expansion tank is required. We had a job years ago where the bathhouse windows of the state parks new windows were blowing out. They called in my father to find out why the AO Smith cooper fin heaters were blowing off so bad as they were on well systems. Turns out the engineer had required a swing check on the inlet to the water heaters. So you had a 100 gallon storage tank and a 200 kbtu fin tube heater with no where to go except the relief valve. The solution was to open the check valves and remove the gates.

Mark Eatherton

What exactly are they trying to protect?

The quality of the water (domestic, potable) doesn't change significantly when it is heated. Legionella and Pontiac fever are present in the cold water as well. What "contamination" are they trying to protect the end user from. What cross contamination are they concerned with?



I understand the code, and the reasons they are put in place, but what you are describing doesn't make sense to this master plumber....



ME

Charlie from wmass

The issue they are trying to

prevent is a matter of opening a cold faucet and getting hot water. Contamination was not the best word to use. Scalding is what the checks on a mixing valve are used to prevent.

Mark Eatherton

So...

Do they require you to run your DHW and circulation return lines in separate joist bays from the cold water lines? Because THAT is where thermal migration comes form, NOT from not having a check valve between the hot and cold and vice a versa. Thermal migration due to expansion IS going to happen whether you want it to or not. The ONLY way to stop it is to not heat it.



Now, if someone can prove to me how it is that hot water will flow INTO a cold water line, other than through thermal expansion, I will buy off on your code requirements. Otherwise, I see it as people not understanding some basic physics here, and throwing in devices (check valves) just to cover their minds eye as to what is happening.



Reminds me of when the wonderful State of New Mexico outlawed expansion tanks hanging from the bottom of air separators. Due to their allowance of non oxygen barrier tubing, the expansion tanks, which are the thinnest piece of ferrous metal in most any system, would be come rotten and fall off the scoop, causing water damage and so on and so forth.



So, instead of outlawing the use of non oxygen barrier tubing, they decided that it was against their code to hang expansion tanks from the fitting for which it was INTENDED.



The only thing they accomplished, was to eliminate the KLUNK of the expansion tanks hitting the floor.... The tanks STILL rotted out due to oxygen impingement from the non barrier Goodyear hoses that were allowed to be installed in these systems..



The inspectors and code authorities are well intentioned, I am sure, but their actions are unwarranted and misguided and cost the consumer money for no return on the investment. They would be much better off and further ahead REQUIRING properly sized potable water expansion tanks on ALL domestic hot water heating systems, because MOST water meter manufacturers have incorporated a check valve into the meter yoke, and it creates a closed system that will cause DHW tanks to balloon, and or T&P relief valves to leak. This is in an effort to comply with a federal law that was enacted clear back in the 1970's and 1980's, that being the Clean Water Act. The elimination of the use of lead solder was a direct action of that act. Funny thing is, you can still walk into ANY hardware store and purchase good ol' 50-50 solder...



The soap box is now free :-)



ME

Charlie from wmass

Mark this is how it happens

The cold supply that feeds the bathroom is valved in such a way as it is shut off while leaving the hot water tank fed with water. The cold faucet is opened and the flow goes through the mixing valve through the cold water line to the fixture.The other side of the fixture is being supplied by the hot water and the faucet gets full water heater temp to it and no matter the position the water coming out is hot and scalds the person. Cases have happened or they would not have thought to include it in the code I am sure. Then you have the case of water due to poor thermal trapping or none at all circulating to fill the cold water pipe when the single handle kitchen faucet is fitted with those wonderful flow stoppers and left on, you know the type with the little toggle or push button to stop flow while you lather up the dishes to conserve water.

Mark Eatherton

Still not seeing it in my minds eye...

Charlie, if you can make a sketch, I might be better able to see it.



I guess if it works for you, it is OK, but in my minds eye, pressure flows from high to low, and it follows the path of least resistance. If we as plumbers are required to cover EVERY potential, our lives will be MUCH more complicated than they really need to be.



Protection can only go so far.



Make me a drawing.



ME