Heating zone piped off domestic water heater

LIBob51

I had a call today for too much heat which made me a little bit concerned. The customer had an old Williamson furnace, and a 30 gallon Bock water heater with a zone piped off of it which is heating an extension on the house. The zone has a Taco 006 and a Honeywell zone valve, the kicker is this zone isn't covered under his service contract. I found that the rubber stopper inside the zone valve had been eaten away, which I have to assume was caused by aerated water flowing through it. I ended up not replacing the zone valve, as the the customer didn't want to pay the price. My question is, could this setup have any adverse effects? I have to imagine the water sitting in that zone could become stagnant during these summer months, and would hate to hear someone got sick from this system. I did recommend a boiler for this account, or at the very least a heat exchanger to separate the domestic water from the heating zone. Whether or not either will happen, I have no idea. But at least I know I'm covered if anything does happen

Ironman

Can You Say: "Legionellaa"?

You did the right thing recommending a boiler or heat exchanger. The Taco X Pump Block would work. Of course, they would also need all of the ancillary components: Fill/back flow, expansion tank, MBR, relief valve.

Jells

That's a common setup round here, I have 4 of them

I have 4 apartments with that kind of setup, they're 450 sq ft.  Oldest is about 8 years, no problems whatsoever.  The only special gear is either a bronze or stainless circulator, taco makes one with the control built on with a wired wall plug.  You literally just stick in the thermostat wire and plug it in.  It's the simplicity that's so appealing, and fraction the price of a wall mount condensing heat & DHW unit, with none of the service concerns. The Taco Block looks interesting, but has so many more parts, 2 circulators, expansion tank etc.



Why would the neoprene rot from DHW temps? It's been used in HW gate valves forever, right?  But my units have no zone valves, with 1 zone why would he have had one?

LIBob51

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Legionnaires' is what I thought of first, but I was taught that was caused by low hot water temperatures. It does make sense though, considering that if the zone valve was functioning properly that once the thermostat called and the valve opened, the water returning would be somewhere around room temperature, while the 4006A was set for 130. I'm just wondering how much a 3/4" zone heating two average sized bedrooms with about a 15~20 foot run between the baseboard and the water heater could affect the 30 gallon tank. But regardless, it's still something I'm concerned about. Hot water tanks average about ten years around here, and this customer told me his was twelve. Even if he doesn't take my advice, I hope whoever replaces the water heater is smart enough to refuse to keep this system as it is.



To answer Jells' question, I didn't say it was the temperature of the water that ate away at the neoprene, but the air carried within the domestic water. Zone valves are meant to be used within closed loop heating systems, while a domesric water heater is open. Let's not forget that water entering a closed loop system becomes dearated over time, if installed correctly. How many gate valves have you seen that didn't hold when closed? It's the same thing as the ball inside the zone valve rotting away, right?

LIBob51

Street Pressure

With the water pressure entering the house between 60 and 70 psi, a flow valve would pretty much serve no purpose at all. What other option is there?

Plumdog_2

Are HW zone Valves rated for potable water?

I've seen oxygen in open systems rust away the steel stems holding the ball, and the ball gets stuck in the valve, forced in there under pressure and stuck REAL GOOD, with the body completey full of rust. Not something I would make coffee with, or wash my dishes with either! Particularly when there are 6-7 more just like it on the same system, and they are ALL rusty. I tell the customers they have what I refer to as an "Alternative" system; which is not code in all locations, and for good reason, then offer to upgrade to something safe.  

Plumdog_2

Are HW zone Valves rated for potable water?

I've seen oxygen in open systems rust away the steel stems holding the ball, and the ball gets stuck in the valve, forced in there under pressure and stuck REAL GOOD, with the body completey full of rust. Not something I would make coffee with, or wash my dishes with either! Particularly when there are 6-7 more just like it on the same system, and they are ALL rusty. I tell the customers they have what I refer to as an "Alternative" system; which is not code in all locations, and for good reason, then offer to upgrade to something safe.  

Jells

I understand the O2 difference

LIBob,



I understand the O2 difference, what I was saying was that the same material is commonly used in DHW valves, it's not immortal, but it's not expected to have a very short life in O2 environments, unlike black iron for instance.



But like I said, there was no need for a zone valve to begin with. As for Legionnaires, if the heater is running 140, the water that might sit the off season should be sterile for those bacteria. And when it starts again it runs back into a 140 heater and anything in there is killed, no?  Who drink hot tap water anyway? I was told as a child not to, that it contains all the crap dissolved from the DHW system.

Jean-David Beyer

if the heater is running 140,

"if the heater is running 140, the water that might sit the off season should be sterile for those bacteria"



I very much doubt it will be sterile. Heating water to 140F will kill a lot of the bacteria, but by no means all. It is sort of like Pasteurizing milk. In Europe, they do sterilize the milk, and it does not need to be refrigerated (until opened), but in USA, it is only Pasteurized; i.e,. heated enough to kill most of the bacteria. Pasteurized milk must be kept quite cold (but above freezing), and probably keeps only  a very few weeks. They do not sterilize milk in USA because people do not like the taste of it.



I get the impression that to sterilize the water, you would want to heat the water considerably over 160F in the pipes and so even higher in the tank.

Jells

I suppose it IS more complex

I guess the question, and I gather there's plenty of debate around this re tank heaters in general, is how hot is safe at all, even boiling isn't truly "sterile". My impression was that a tank at 140 was safe for Legionella, and why you should always run them hot with a tempering valve. Sure there's plenty of bacteria that survive hotter, the reason why you need to use a pressure cooker for canning anything but jam is that 212 isn't hot enough for botulism.  But I've heard no one talk of botulism in water heaters, just of what actually can live in there.



So when that zone starts up and the 3.5 gallons in the zone are circulated back into 40 gallon WH @140, I would think any live Legionella are killed.  Note that both Rheem & BW make tanks with additional side taps for this room heating purpose.

LIBob51

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I've never seen either of those tanks, but I'm wondering whether or not the installation manuals actually say those tappings are intended for space heating

Ron Jr._3

Saw this setup once

We were there to replace about 30 feet of Slant fin baseboard . The elements developed pinhole leaks all over . The thin copper in them wasn't able to handle the higher pressure and fresh oxygen brought in everytime someone uses hot water .  I can understand why it wouldn't be covered under a service contract .

Jells

Yes it WAS designed to be used for heat!

LIBob:



Here's just one of a number of Rheem models with this feature. The one I used last was a 40 gal, but I don't remember the model. The manual WAS explicit, including zone diagrams.



http://www.rheem.com/product/residential-gas-water-heaters-fury-heavy-duty

"Side water connections for space heating applications for 48, 63, 75 and 98-gallon models" 

SWEI

better not be much of a heat load

They're quoting a .49 - .58 EF on that beast.

Jells

No, it's not for a big load

Like I said, the units I used it in are 450 sq ft.  I was working on a top floor unit in January with the heat off, and the room temps didn't dip below 60.  Doesn't take much to get it up to 70.  They get hot in summer though!

EricAune

Sure it may be common...

"Just because you can doesn't mean you should"  That's what the old man used to say often and it's true. 



There are many reasons why this may not be a healthy and efficient system.  Bacteria, stagnation are first to mind.  Add the fact that most conventional products are not engineered and rated to be used in an open system.  Oh, and then there's this little thing [at least where I reside] called a plumbing code that addresses this exact situation and outlaws it from the get go.

Mark Eatherton

Oh how I wish your code was EVERYWHERE...

Just because the manufacturer allows it doesn't mean its a good idea to do it...



Remember, the manufacturer has one goal in mind. SELL WATER HEATERS.



If they were smart, like their European counterparts, they'd understand the extended liability associated with water born bacteria and its impact upon human beings, and they wouldn't allow it. Unfortunately, our code approval process is driven by money, and if you have enough money, you can get ANYTHING approved. Such is the case with dual use water heaters.



Some AHJ's have gotten smarter, and disallow their use. Jefferson County here in Colorado is one of them. You can do it, but it requires a heat exchanger between the two fluids to make it work. And then, it won't work real well when it needs to, so it gets a bad name. Kinda like staple up off the internet systems...



ME