Replacing boiler on a gravity system?

[Deleted User]

I am looking at a job to quote. the system is about 100 years old. The boiler is an American Standard #7. fires around 250 mbtu. There are two 2 1/2" supply lines out of the top and the same on the bottom for returns. I' sizing a boiler at 175 mbtu. Any input on piping? Pumps?

Steamhead (in transit)

Get the total EDR

and size your system circ to that value. Use the chart at the link below:

http://www.heatinghelp.com/newsletter.cfm?Id=125

Of course you'll size the boiler to the heat loss regardless of the EDR count. If the boiler manufacturer requires a certain circ for the boiler, use that one.

Most boiler manufacturers call for either a bypass or the use of primary-secondary piping to make sure the boiler doesn't get too much cold return water. I prefer P-S, since it also decouples the system circulation from the boiler circulation.

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