Re: extending a steam system

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Posted by Harold Kestenholz - Hydronic Network on May 03, 2001 at 09:45:58:

In Reply to: extending a steam system posted by kevin pvimage on May 03, 2001 at 04:33:02:

A steam boiler must fill the entire system with steam in less than one hour. If the boiler is too small to do that, parts of the radiation system will not heat - there is no way to predict which sections will not heat then. If you add more radiation than the boiler can fill with steam, you will not have a working system.

You can find how much output is in the system now that heat is not required by opening the windows and turning the thermostat up. Observe and time how long the boiler runs until the burner shuts off on the pressure switch. If the boiler shuts off in less than 40 minutes, you can extend the system - as the output of the boiler is less than that required to heat the radiation over one hour. The radiation is therefore less than that required to be filled by the boiler output over the time of one hour.

There is free instruction on how to size cast-iron steam radiation at

Proper piping with enough slope to return the water to the boiler without forming a puddle in the pipes is important to prevent banging in the pipes and blocking your heat.

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