Pressure relief valve for OPEN gravity system

Narendra Varma

I have an OPEN gravity system (about 100 yrs old) with an oil boiler. There is an expansion tank in the attic with an overflow leading out the roof. I am trying to sell the house and the buyer's inspector is claiming that the system needs a pressure relief valve at the boiler. This makes no sense to me since the system is open but the inspector is claiming that the code requires it.

I will check with the city authorities on the code but it seems ridiculous to me to have a pressure relief valve on an open system. Any opinions on this matter would be greatly appreciated.

All the near-boiler piping is 3" IPS wrapped with 2" of asbestos insulation. I really don't want to have to remove the asbestos and mess with the piping to install a relief valve. If necessary, can I install a pressure relief valve on the boiler fill pipe (between the boiler and the back-flow preventor)?

Thanks,

- Narendra Varma

Alan(CaliforniaRadiant)Forbes

It could happen

that your open system becomes a closed system if the vent from the expansion tank gets clogged. Current codes are there to protect life and property and it's in your best interests to install a relief valve.

You will probably have to install the relief valve on the large diameter piping unless the fill line is larger than ½". If it were me, I would drill and tap one of the 3" lines to accept the relief valve.

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Aidan (UK)

PRV

I would prefer to have a PRV on every boiler; some standard specifications I've used require PRVs on all boilers and water heaters. It might well be that this is what your code requires.

The open system could become a closed system if the open vent and the cold feed pipes were to freeze. I don't know where you are. If the open vent does discharge onto the roof, it would be prone to freeze. This pipe usually discharges over the feed & expansion tank.

A work colleagues recalled seeing a house, with a coal fired boiler on which the feed and vent pipes had frozen; this was probably in the '50s. The boiler had burst, demolishing the side of the building.

Ken_8

Ask the inspector

to show you the code he refers to.

Most mechanical codes require presure relief valves on all new installs. This however is not a new install!

It is not outside the realm of "normal practice" however for inspectors to demand things that would be normally "grandfathered in" to be usurped by the fact that the buyer will inheret whatever you leave behind. On THAT basis alone, it may be code to "upgrade" all so-called "life safety" items at this time.

In other words - find a threaded hole that is now plugged somewhere in the boiler block and install a properly matched BTU capacity safety relief and end the debate.

But then too, you could suggest the cost of the relief valve can be taken off the asking price... And the buyer put it in?

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Narendra Varma

How do I size the pressure relief valve?

Thanks for all your responses!

I get the message! I understand that the open system could become a closed system due to some unforseen blockage. So, here's the next question: How do I size the relief valve? The burner is currently set to burn 2.5 gallons of oil/hour. Yes, it's a very large house!

Also, any idea what a valve might cost me?

Thanks,

- Narendra

Narendra Varma

How do I size the pressure relief valve?

Thanks for all your responses!

I get the message! I understand that the open system could become a closed system due to some unforseen blockage. So, here's the next question: How do I size the relief valve? The burner is currently set to burn 2.5 gallons of oil/hour. Yes, it's a very large house!

Also, any idea what a valve might cost me?

Thanks,

- Narendra

Ken_8

You need to know three things:

1) The size of the thread you will discover within the boiler block itself - now plugged; you're going to remove it and install the safety relief valve in it.

If the "spare" hole you find is 3/4",that's good. If it's 1", that's better.

2) Fawgettabowt the size of the current nozzle. The safety valve is not sized based on actual BTU's at this particular moment, but rather, the maximum BTU input capacity of the boiler itself! Somewhere on the thing is a "boiler plate." On it will be the information you need to get the correct valve.

Get a safety relief valve for a water system (not steam) that's set for 30# (unless you run higher pressure?) and put it in the spare plugged hole you are going to find.

3) If you get lucky, and you find a spare hole, it may be possible to take the last few threads out and quickly shove the new safety relief valve without much of a bath. The trick is to close the valve or place plastic or something over the vent so that when you dump a few quarts, a vacuum is created and you minimize the glugging and air contamination - as well as avoid the hassles of dumping and refilling jillions of pipes and rads.

And Narenda? This is a little above most home owners and would not cost a fortune to have a pro do this, you know.

If you lived within 20-30 minutes of my shop, I'd charge you a little under $500 for both labor and materials.

But let me warn you. DON'T CALL ME AFTER YOU STRIP THE THREADS OR CRACK THE BOSS WITH THAT 6-FOOT CHEATER BAR I SEE YOU HAVE HIDDEN THERE...

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