Gravity conversion

Lynne

Yet another existing gravity system in little Keene, NH, that we are going to convert. It is one with two 1-1/4 headers, the largest pipe in the system being 1-1/4. According to Dan's book, the new boiler piping should be 1/2 the pipe size, then drop one size down. That would make it 1/2"? And where does the reduced piping begin, after the circulator?

Mike T., Swampeast MO

Are you absolutely certain...

...that it was a gravity system? 1¼" is VERY small for a gravity system considering the smallest tap size [I've seen] is ¾". I don't have the proper books here but I think that a 1¼" main would serve NO MORE THAN TWO radiators, each tapped ¾".

When you convert a gravity system to forced flow you...

Bring the return pair together IMMEDIATELY sizing down by the ½ - 1 pipe size method. Continue this size THROUGH THE CIRCULATOR AND BOILER until JUST BEFORE the point where you connect the supply pair.

Lynne_2

Gravity conversion

Yup, sure it's gravity, no circulators, tank in the attic. There are two supplies, both are 1-1/4, I will double check with the guy who looked at it. Even if he was mistaken, and they were 1-1/2, that would still give us 1/2". Thanks for your input.

Steamhead

Lynne, is there a strange-looking device

installed in the pipe leading to the expansion tank? Possibly with the name "Honeywell Heat Generator" or "Klymaxx Heat Economizer" or "Phelps Heat Retainer" or similar?

If so, that would explain the pipe sizes. These devices allowed the system to develop a small amount of pressure so the water could be heated beyond the normal boiling point. Gravity circulation at these higher temperatures could work with smaller pipes.

Nowadays, we use closed expansion tanks and circulators to do the same thing. I would pipe a replacement boiler in this type of system the same as on a newer one.

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Lynne

Hmmm

I'll look for that. The system is just like Dan's picture in How Come? of an upfeed system. So, you'd stay with an 1-1/4" header? Thanks again.

Steamhead

I'll wait

for the results of your search to answer.

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