Since all of the components.............hb

heatboy

75 psi and I'm running a small radiant system from an instantaneous electric heat source, why do I need a compression tank and 30 psi relief valve? The unit has a T&P valve on it and water temps will never go above 110°, so........?

hb

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Brian (Tankless) Wood

And, your point is

? Was there supposed to be a pic with this post. I used to be a psychic but I'm OK now :O)

Which tankless unit did you use in your invisible system? I'm sure it'll be wonderful when it shows up.

Tankless in Swampland.

hot_rod

Why

I have done a dozen or more 2 and 6 gallon electric tanks that way. In fact I don't use a fill, 30lb relief, expansion tank, or air purger! Some have LWC if the radiant is below the tank.

I fill to about 12 psi, they run up to maybe 35 lbs. at 110F setpoint. Works for me.

hot rod

Glenn Harrison

Correct me if I'm wrong,but...

isn't a standard T&P set for 150 p.s.i. That would be an excellent reason to put on a 30 pound relief on a 75 pound rated system. Of course, then you would need a expansion tank too. J.M.O.

Glenn Harrison, Residential Service Techician

Althoff Industries, Crystal Lake, Illinois

Althoff Industies Link

John@Reliable_2

How about this for a reason?

Because the "heat source" is now a boiler and no longer a water heater. If something was to go wrong I wonder what the installers liability would be for not treating the heat source as a boiler? I'm sure standard industry practices would be heard coming out of a lawyers mouth at some point. I have never though about this until now heatboy, and I may be all wrong. But for the price of a prv,tank,feed valve mmmmmmm! CYA I say. John@Reliable

Al Letellier

why???



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Al Letellier

why???

Plain and simple.It is a boiler when it is used as a heat source and check the code!!!!!Our plumbing codes and heating codes require 30#safeties, feeder and backflow preventer, an expansion tank is a must and here we also require a low water cut-off on ALL boilers.

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Brian (Tankless) Wood

Hi Al

the Seisco that HB plans on using, has a built-in lwco, and it works lightning fast. The larger, four-chamber models have two lwco's.

Just bringing a little clarity.

Happy heating, y'all.

Swampster.

Brian (Tankless) Wood

Hi Al

the Seisco that HB plans on using, has a built-in lwco, and it works lightning fast. The larger, four-chamber models have two lwco's.

Just bringing a little clarity.

Happy heating, y'all.

Swampster.

Oops, double-click. Sorry.

rich pickering

but.....

water heaters are not built to the same standards as boilers which is why csa won't allow them as a stand alone heating source. So, if they aren't considered a boiler by the manufacturer or the regulators, what is our liability as installers? I've used them in the past, with relief valves and tanks, but not any more.

hot_rod

Correction to my post

I, too, argee the 30 lb. relief in addition to the factory 150/210 would be wise. After reviewing my past installs I do add this additional safety. Although I still find they run fine without expansion tanks. I also feel installing a fill and backflow and leaving it turned off is odd, and unecessary

More and more water heaters are coming from the factory with labels indicating they are suitable for heating applications. I'm not sure how various codes, and code officials "read" that!

Consisering the tanks are tested and certified to 150 lb working, and 210 degree relief, personally I feel they are SAFE to be used in closed loop heating applications. Especially considering the 12-20 lb typical working pressure in heating only applications.

The pressure test on a water heater far exceeds the 45 lb test that boilers are required to meet. Actually water heaters are tested at 300lbs.

Depends on what the code folks (in your area), the installer, and the homeowner are comfortable with.

hot rod

Tom M.

In a closed loop

In a closed loop with all the air removed, any increase in temperature would cause a rapid increase in pressure. In your picture above, I would guess that there is an air pocket in the top of the tank acting as an expansion tank or the flexible piping is stretching to accomodate the expanded water. With the small water volume and, I assume, low supply temperature, it wouldn't take much but there has to be room for expansion somewhere.

Tom M.

David Van Wickler

If your so comfortable with the 300lb rating

why do you put a pan under the water heater? Do you put a pan under a boiler??? Just kidding......Probably beats piping the relief to a drain!

Tony Conner

Depending Upon The...

..."codespin" in your jurisdiction, your assembly could very well fall under something like the ASME B31.1 Power Piping Code. The safety or relief valve setting is pretty much the determining factor. The ASME folks don't care what the operating conditions are - when they say "design pressure", they mean the setting of the safety/relief/rupture disc. Once you cross the line, now everything - every piece of pipe, nipple, fitting, valve, heat emitter, expansion tank, etc. - must have code approval for the design pressure & temperature. Not only that, but YOUR ASSEMBLY of these components must be hydrostatically tested to 1.5 times the safety or relief valve setting, and witnessed by the inspector. This is not hard to do - it's done all the time. But not normally in residential building heating.

If you do something, like change a relief or safety valve setting, that pulls you out of one code classification, and/or drops you into a new code classification - get ready for some adventures on the learning curve. All of a sudden, a whole new set of rules apply. If I was doing residential building heating, I'd do pretty much whatever I had to, to stay out from under the ASME piping and pressure vessel codes whenever possible.

hot_rod

DVW

nice to see your voice again. All components leak SOMEDAY! Hate to see anything drip on his fly tieing equipment located on the work bench below! Plus it looks pro.

Yes I put pans under my boilers if they are installed above finished space or valuables, as in this case

Tom, 3 loops of 3/8 pex, 6 gallons in the tank and temperature swings between, maybe 68 degrees to 100 degree setpoint. It's been in 3 years now, with no relief. Maybe I did use a 45 lb relief? How much should 8 or so gallons expand over a 32 delta T, pressure wise, without an air pocket?

Most small wet rotor pumps are listed to 125 lbs, the tube 100 psi at 180 degrees. I suppose a 60 or even 100 psi secondary relief would cover all the suggested pressure maximuns on the various components. The 210 degree relief on water heaters is designed to pop before steaming. It also has the tank mounted snap stat as high limit and the standartd "red button" high limit safety. This gived me triple redundancy on thr temperature (electrically speaking) and the T&P temperature relief. Gas water heaters also include an ECO.

Not many boilers I know of have 4 temperature controls and safeties! And two pressure reliefs. Not sure it gets much safer than that.

hot rod

Tom M.

exp. tank

Although I am considering doing the math on the 8 gallons at 32 delta T, my point would be that I would put a tank on. The smallest one made would be more than enough. Even if you can't fit it into the space, you could run a 1/2" line to a tee to make your point of no pressure change. That way, you control (a)the fact that there is room for expansion and (b) where the expansion is so you know where to pump away from. Also, you won't worry about an air pocket being absorbed into the water and released through an automatic vent over time.

Tom M.

Tom M.

if you're curious...

I got from the Watts website that 40 gal. from 90 degF to 140 degF expands about 1/2 gal. From this, I estimate that the 8 gallon low temp. system will only expand about 8.2 oz. I would still want to know that the extra cup of water always had someplace to go.

Along the way, I found that Amtrol has an interactive sizing tool on their website. Just enter system volume, high limit temp, boiler output and choose from a menu of types of radiation supplied and a tank size will be recommended.

Tom M.

[Deleted User]

If you're talking...

suspended tube, which would be a first for you, I wouldn't worry about it because the tube has a higher coefficient of expansion than does the water. If the tube is bound by plates or cementitious materials, all bets are off.

Otherwise, I'd throw an expansion tank on it. Besides, without an expansion tank, you wouldn't have a PONPC, and your circulator woud be confused. As for the 30# relief valve, it's cheap early insurance.

JM$0.02W

ME

Dave Yates (PAH)

PONPC

Boy, I hate seeing confused pumps!

I'll have a paper with me next week that clearly addresses the legal liabilities (written by lawyers who specialize in LD cases) of potable/hydronic systems. In it they spell out - in terms even I can comprehend - who gets to be the whipping post when we venture into their arena.

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Dale

Thinking about what could go wrong

I was thinking about a standard electric water heater like HR's post. The overtemperature is a fixed 190 degrees that senses the surface of the tank. Is 190 or 200 with the pump running OK in Pex? If the element shorts it just keeps putting heat into the tank until the high limit opens. In a closed system the pressure rises pertty quick and the 150 pound pressure relief drips long before the water gets hot, of course this is with a 60 pound fill. Alot of fill valves leak through so unless you filled the system with a hose pressure can increase. Water boils at 307F at 60psi so the over temp redundancy is the key. I guess as long as you have 2 separate temperature controls to pervent steam at 212 ( code required of all water heaters) you won't get into real trouble. This would mean always leaving the T&P valve in and adding the 30 pound relief if you chose.

Tony Conner

This Would Be...

...the difference between plumbing codes, and boiler & pressure vessel/pressure piping codes. When you venture into boiler & pressure vessel/pressure piping code territory, they don't care about controls, or redundancy thereof. All they look at is safety/relief valve settings.

It's usually spelled out pretty clearly where the dividing lines are between the various codes. Cross the "code line", even accidently, and you quickly find yourself in a whole new game.