Venturis, potable water heaters, heat exchangers etc (ME)

Mark Eatherton1

Last weekend, Big Head Todd asked a question about the use of a potable water heater for doing space heat, and we got PAH all riled, and I didn't finish explaining the recommendations we made to the RPA regarding this issue. Dave said he didn't want to depend on some mechanical means to keep the water fresh in the potable side of the plate type heat exchanger.

I think he thinks I'm talking a mechanical timer. I'm not.

I'm talking a venturi tee on the water heaters inlet where the HX water will be brought back into the tank. This way, whenever ANY water is drawn through the DHW tank, the venturi induces flow through the heat exchanger, thereby keeping the water fresh and avoiding stagnation. I realize that this is not the end all answer, but it WILL keep the water in the heat exchanger from becoming stagnated.

Some componenets (check valves, isolation valves, drain valves etc) have been eliminated for drawing clarity.

Ask away!!

ME

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Dale W.

Venturi Tee

Mark,
This does look like a safe and very simple way to add a small zone. Would the venturi tee be like a monoflo tee?
Dale W.

Mark Eatherton1

Functions the same...

but does not have as high a pressure drop as a one pipe monoflo fitting. There is an insert fitting made by Nibco specifically just for this purpose.

ME

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Dale W.

Not a stock item?

Mark,

I'm guessing the supply houses probably don't stock this venturi insert. I think I'll visit them and get a couple stocked myself for when I need them.

Thanks,
Dale W.

Mark Eatherton1

I get mine at

a local wholesale house called Water Systems,Inc. 303-629-6122 They keep them on their shelves. They're in their (Nibco) catalog.

Here's an exploded view of a double venturi tee I made for my one pipe heating system in my home. I'm using Buderus radiators, which have a 2" O.C. tapping, and to be sure that I flowed enough water through the radiators, I invented this diverter/venturi tee. The left hand insert is a 3/4" fitting X 1/2" copper reducing coupling that I cut the "excess" fitting off of and put it into the inlet tee with the cone facing upstream.

The right hand insert is the actual Nibco fitting. It's cone faces down stream of the flow. The reason I opted to use the reducing fitting in the inlet tee is because it has a "fatter" appearance to the profile of the water flow when looking at it from the end.

Forgot to mention, I had to "modify" the length of both tees because unmodified, it came out to 2-1/2" OC, which won't work for 2" OC radiator tappings. This is legal provided that the pipe inserts into the fitting by at least 1/2 the diameter of the pipe being served. Watch your fingers around the ol' copper chop saw when performing this feat!!

ME

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Mark Eatherton1

Here's the one pipe diverter/venturi fitting in place.

This is a portion of the one pipe main that runs around the ceiling of my office. This serves the radiator in my front room. You're looking at the junction of the wall and ceiling.

ME

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Mike Kraft

Question from the back!

Are you using two venturi inserts in this particular install for the office rad?(S&R) This creates enough drop so the spacing between the tees is (in this case)almost nothing?When I install panel rads for baths etc. on a series loop I typically am upfeeding and space my venturi at least 8" if not more (on the return) and my feed tee is a straight 3/4"X1/2" tee.

I too have a local supplier who stocks these inserts and I keep a couple in the truck.

cheese

Mark Eatherton1

Venturi in both

the supply and return. One acts as a diverter tee, and the other as a venturi tee.

I'd been warned by numerous people not to attempt to stack these tees right next to each otehr, but I did it anyway and it works like a champ. I'm only running 3 GPM on the main, that may have a lot to do with its performance. If it were a higher GPM and consequently velocity, it MIGHT cause some problems.

Thanks for asking.

ME

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