Home Plumbing Question

Hi,
Got to wondering a bit about this.
Have a very typical forced hot water heating system. Also, a gas water heater for the hot water (washing) supply.
I realize that mixing of the forced hot water heating system water, and the home water (washing and consumption) supply is a real no-no, as it should be.
But, I cannot see any check valve on the line going to the furnace from the split on the incoming water supply. Only a pressure reducing valve on the branch going to the furnace. Do these pressure reducers typically have a built in check-valve ?
Or, is simply the difference in pressures enough to ensure no mixing ?
If no check valve, as seems to be the case, how is this separation achieved ? Do more modern systems incorporate, due possibly to building code changes over the years, a discrete check valve ?
Or,...?
Thanks, Bob
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In my experience you typically have a water feed valve on a boiler that regulates pressure and has a check valve built in.
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I think the pressure reducing valve also has a reverse flow preventer.
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On Monday, 14 January 2013 12:49:53 UTC-5, Bob wrote:

Definitely there needs to be a backflow preventer, to protect your drinking water in case of pressure drops which might occur occasionally from whatever cause.
I've been under the general impression (from this very group, fwiw) that (all? most?) pressure reducers are inherently backflow preventers, because it comes up from time to time that people have pressure reducers installed at their main water supply and need to have an expansion tank installed too, since the water main can no longer absorb routine expansion at their water heater.
Now, whether it meets your local code to rely on the reducer for this purpose, I can't guess. I had my plumbing re-done last year as part of a reno and my plumber put in a separate check valve and pressure regulator. Perhaps there are models which are code-approved for both purposes.
I also have a manual valve, which I normally keep closed, which makes the whole question kind of moot. If you don't have one of those, get one.
Chip C Toronto
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No, a pressure reducing valve is not a back flow preventer, and neither one can be considered a check valve. These are all different beasts that serve different purposes.
(See PS about mixing hydronic water with potable water below:)
My understanding is that there's no actual "check valve" per se built into the pressure reducing valve, but the low pressure of the hot water heating system (typically about 12 to 16 psig) prevents back flow of water into the water supply piping (typically 40 to 80 psig). That is, water won't flow against a pressure gradient any more than it will flow uphill.
Where I live, in Winnipeg, Manitoba, there's a city by-law requiring a "back flow preventer" on all commercial boilers (which includes hot water heating boilers in apartment blocks). The concern is that if the pressure in the water supply piping drops to 0 psig, or event drops below atmospheric pressure, then the low pressure or partial vaccuum in the supply piping could suck the hydronic water out of the boiler through the pressure reducing valve. A back flow preventer senses that drop in pressure and allows air to be sucked in to the water supply piping instead of the hydronic water. In that respect, it differs from a check valve.
PS: Drinking hydronic water. It's water from the same water supply piping that supplies both your kitchen sink and your boiler with water. So, where's the concern about mixing potable water with hydronic water? I never understood that concern.
In a hot water heating system, the new water that goes into the heating system has both dissolved oxygen and hardness ions in it. With a few days of heating that water, the hardness ions precipitate to form "scale" in the hottest parts of the heating system (the boiler). Also, the dissolved oxygen reacts with the iron in the system to form a black form of iron oxide (Fe3O4, I think) which causes the hydronic water to gradually turn black. And, rust isn't poisonous. It's not as healthy to drink as a V8, but from what I know, it's no more harmful than drinking rusty water from rusted cast iron piping before it clears.
Once the water in the heating system is both oxygen depleted and ionically dead, no further changes occur to it except that it repeatedly gets hot in the boiler and cools down in the radiators.
So, unless someone is using corrosion inhibitors in their hydronic water, I really can't see why drinking hydronic water would be unhealthy.
And, in fact, I know a girl who spent time in Russia prior to the Soviet Union collapsing in the early 1990's, and it was common for people living in apartments there to open the air vents on their heating radiators to get hot water out of those radiators for cooking and cleaning and making tea. The reason why was because electricity was unreliable, and so if you had an electric stove, you couldn't count on there to be the electricity needed to heat the water in your tea kettle 24 hrs a day like we've come to expect here in the West. So, Moskovites would use the water out of the building's heating system (which was heated with gas or heating oil) to make tea and for cooking supper. And, the building maintenance people would intentionally not use corrosion inhibitors in the heating systems because they knew people were drinking that water and using it for cooking.
I'm not encouraging people to sample the water from their heating systems for taste. I'm just disagreeing with the premise in the original post that "I realize that mixing of the forced hot water heating system water, and
the home water (washing and consumption) supply is a real no-no, as it should be." I just don't see where the no-no comes from if nothing is added to the water after it's entered the heating system.
--
nestork


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That's not true. Water feed valves for boilers typically have a check valve built in. On older installations, that may be all there is.
That is,

It's *not* the same water that supplies your kitchen sink. The water goes into the boiler for the heating loop and stays there pratically forever, going round and round. Through components that were never rated for drinking water. If that water accidently makes it's way to the ktichen sink, would you drink it? And then you have the issue that some systems add antifreze for protection.
If the boiler has a loop for providing hot water to the sinks, it's a SEPERATE loop, designed and rated for drinking water. Fresh water is constantly flowing through it and that water is entirely seperate from the water flowing in the radiators.

Then you are OK with drinking it. Go figure.

It was also common for them to die at 45.

Maybe you should think about it again.
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Makes me wonder about the boiler for steam heat in a house i rented. When the heater quit working, I somehow found by opening a valve, water would flow into the system, and the system would fire up. I then would shut off the valve. I didn't live long in the place, or what was like a fraternity house, but I seemed to be the one getting things done, including getting fuel oil. Oh then I got selected for the army. Long time ago.
Greg
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I wondered if the system was automatic filling, but I shut off the valve to be sure. Seemed odd that you would have to manually fill every few weeks.
Greg
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You really don't want to be drinking heating system water even if there are no additives, as is usually the case in residential.
When it comes from the water supply provider it has disinfectants in it, either chlorine or chloramine, but those disappear quickly and the bugs begin to grow. Bacteria, slime, etc. Look at what comes out of a fire sprinkler system sometime, it's black and slimy. Water has a shelf life that is long exceeded in a heating system.
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