Why can this not be done?

If you built it, they will come.

A water heater sitting idle for six months is infinately preferrable to you being idle 6' under the lawn for ever. Isolate the two fluids and use some simple mixing strategies. And just for the record, 140 degrees is just about right for domestic hot water. The point of use mixing valves are not needed until you get to within a few feet of the bathing module & at that point you can reduce the temps to 110 degrees for much safer temperatures. 120 degrees F is not the safe temp you think it is! Details appearing soon in a magazine near you(G)

Legionella bacteria need just four things and not all need to be present for their enjoyment.

* Water temps between 50 & 133 degrees F

* Biofilm (found in all potable & open system piping & vessels)

* pH between 5.0 & 8.5

* Stagnation & for bonus points? - added volume, which your open system adds nicely.





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One size fits all?

Sounds like your contractor only knows one way to do the job. One system does not solve all problems in the radiant heating world. A good heat loss is a start to finding out how close the tubing should be and how hot the water needs to be. If you want cooler water temps look at putting the tubing on top of the subfloor with distribution plates. Knowledge is power. If your contractor doesn't know then you need to get a new contractor or set about getting your own education.

Seriously consider the warnings about the bacteria. Having a heater sit idle for 6 months of the year is cheap insurance. No one fully understands the bacteria world and how it interacts with your body and pre-disposes you to other diseases even if the disease causing agent is not found in your water system. My wife is a microbiologist and she had one thing to say about open systems, "Not in my house and hopefully not in any house I visit."

Larry Ticknor

Thanks Cas

Would you believe, there's a heat pump system on the market that grabs potable water from the street main, uses it to produce heat or cooling and then returns it to the main? Now that's crazy! Kinda rules out the need for backflow preventers, eh?

Not upstream from me bubba.

Fortunately, our local water co saw to it that these systems can't be installed here.

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Didn't mean to single out

Bradford White, I have been and still am selling these water heaters by choice. The same goes with all the indirect water heaters we install every day. I guess I was just wondering how we technically decide how much protection is enough....
Cas

Potable water protection in open heating systems

In our area an open heating system is approved by our local Dept of Health as long as all materials are approved for potable water and if a pump with a 365 day timer is installed in order to cycle the heating system for 1 hour per day.This is UPC country which is a fairly stringent Plumbing Code.

point

Who will know when the pump fails? Got stagnation? Once a day injection of stagnated potentially bacterial laden water? No thanks.

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double wall HEXs

...are required in san francisco between domestic & non-potable water...

another point

I've seen examples of what you refer to. Great theory except that it ignores pressure & flow problems created by running through hundreds of feet of small diameter tubing. Scalding and extreme loss of flow as downstream or lower floor fixtures are utilized.

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With pleasure! Here's an article I wrote on this very subject.

Article title - "Here's Your Sign"

BILL ENGVALL’S song, "Here’s Your Sign," plays in my mind at times. Like
when I see a water heater with a 3/4-in. cold water feed line and a 1/2-in.
hot water outlet. Why do that?

Or when I’m told that open-system, cross-connected potable-hydronic systems are so great because
they give you free air conditioning and increase the capacity of your water heater by as much as
50%. All of which can be done without any risk to your health because all the incoming cold water
will be run through the radiant heating system on its way to the water heater and, therefore, prevent
stagnation of potable water along with tempering the colder well or municipal water?

Those were the claims made during a heated e-mail exchange in which I was told, "You just don’t
get it!" In yet another e-mail regarding open-system construction, I was told I’m "just a dumb
(expletive deleted) plumber." We’ll address the slam about being a plumber in another column.
Where’s my sign?

Aside from the potential health risks associated with open-system construction (see
http://www.contractormag.com/ articles/0401/legionair.html), there’s the issue from last month’s
column regarding pressure losses and balanced flow in plumbing systems using potable PEX water
lines. It’s an issue ignored by many proponents of these systems, but one that exposes the customer
to potential scalding or poor delivery pressures as downstream or lower floor fixtures are used
simultaneously with the upstream or upper floor fixtures.

Now before anyone gets his boxers in a bunch, let’s take a minute to examine some hard realities.
Line lengths for 1/2-in. PEX hydronic systems are often 250 ft. Systems connected to a
combined-use water heater will have fairly small Btuh loads in order to permit bathing without
losing too much capacity, right? If not, they need their own dedicated heat source.

At 250 ft. and using the chart from last month’s column, which shows a .208 pressure drop per foot
with a 4-GPM suggested maximum flow rate, these systems are dealing with a potential 52-PSI
drop during peak flow conditions! That’s before adding losses due to elevation changes and line
lengths to fixtures. Here’s your sign.

But let’s change that to heating an area with 1,000 ft. of 1/2-in. PEX using four 250-ft. loops
attached to a manifold.

The shower on the third floor (loss of 10.4 PSI for the change in elevation of 24 ft.) is being used by
Mr. Jones who loves his high-flow, 8-GPM showerhead. He’s adjusted the faucet to compensate for
that long four-way-split-run pressure loss and the differential from the lower resistance to flow in the
cold water line. He’s using an 80%/20% mix of hot/cold because of the 55°F well water and the
heating system, which was already running, has lowered his storage temperature.

With 6 GPM to split between the four hydronic loops, he’s got a pressure drop of 8.5 PSI (.034
PSI/ft. x 250 ft. @ 1.5 GPM). But wait a minute, we’re not including the 75-ft.-long run of 3/4-in.
PEX from the water heater to Mr. J’s shower! That’s another 75 x .082 (3/4-in. PEX at 6 GPM) for
another 6.15-PSI loss. That’s 10.4 + 8.5 + 6.15 for a total line loss of 25.05 PSI!

If Mr. J’s pump system is set at 20/40, he’s toast. Even if it’s set up to operate at 30/50, there’s going
to be trouble brewing the instant a lower floor or lower-resistance-to-flow fixture is used. If you were
water, which way would you go? Here’s your sign.

Well water systems contain higher levels of organic material than most municipal systems, which
means greater odds for biofilm in the tubing and, therefore, more amplifiers for bacterial growth.
Low flow in long horizontal lengths of tubing, no matter the materials used, promotes
sedimentation and biofilm layers. Here’s your sign.

Free air conditioning? OK, let’s introduce that 55°F well water into the 1,000 ft. of in-floor PEX
tubing for the 15-minute duration of Mr. J’s shower. Will this chill the room appreciably? Will the
tubing sweat if it’s installed in a staple-up underfloor application and sees humid basement air?
Will Mr. J need to lay flat on the floor to appreciate the benefits?

If Mr. J is on a municipal system, he won’t be getting chilled water and will likely be receiving water
at or above his room’s air temperature during those peak air conditioning load days. Do the
"benefits" outweigh the pressure, flow and health-related issues? Here’s your sign.

What about the claim that such a system increases the capacity of your water heater by up to 50%?
That assumes the floor is heated to its upper limit, the circulator is running and the water heater
has just finished recovering to full temperature. You know what they say about the word "assume"!
Here’s your sign.


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An atta boy(G)

for the lead in.

All of the tubing manufacturers have flow and pressure charts. Some require a bit of digging to find and the various fitting types can have an affect too. Once you find their info, it's just a mathematics game.

Proper sizing methods for copper systems are essentially ignored too.

There are a number of people who hold very strong opinions that open systems are perfectly safe, but we're working on them! There are several internet DIY sales companies that actively promote open systems and at least one that sells tubing many here feel is sub-standard. Let the buyer beware.

I always felt that open systems were wrong, but it wasn't until a few years ago that I had anything more than a gut feeling to go on. When you stop to think about the Legionella issues, it's only been a few years since the bugs were discovered and the knowledge keeps changing on an almost daily basis. As a result, there are a tremendous variety of opinions regarding how to deal with them and what the proper potable hot water storage, distribution and point of use temperatures should be. The ASPE convention just ended yesterday and that was one of the main topics. It will be interesting to see what changes will come out of that meeting.

Keep in mind that the open system construction idea was brought about back when water heaters came set at much higher temps and the systems installed were copper baseboard. Low temperature systems with favorable bacteria criteria were unheard of, PEX wasn't around and Legionella had yet to be discovered. That was then, this is now.

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closed systems and water heaters

There are times when water heaters make perfect sense - providing they are closed loop systems either as stand alone or isolated via a heat exchanger. The heat emitters don't care where the Btu's come from. The jury is still out on system longevity where water heaters are utilized as stand alone with water that remains contained and constantly reused. If barrier tubing is utilized, then free oxygen is kept at bay. Under those conditions, I would expect a much lomger than normal life span.

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