Boiler supply and return pipe size

kinghoward

Replacing current boiler that has 3/4 inch supply and return pipes going into the bottom of cabinet. It is orange pex with galvanized union connected to boiler. The new boiler has 1 inch size supply and return. If I get the fittings to go from 3/4 to 1 inch....first does that cause any concerns and second any suggestions how long should I make the 1 inch section going to boiler. And third why do they use 1 inch when alot of systems are 3/4? Thank u

mattmia2

depends on what the old and new boiler are. if it is a mod con it may need to be piped primary-secondary to get enough flow.

kinghoward

Ok...these are 80k btu boilers (condensing) for a residence. I'll ask the manufacturers. Thank you

hot_rod

https://forum.heatinghelp.com/discussion/comment/1861910#Comment_1861910

The manufacturers installation manual will show piping options. They are all online these days.

To move 80 thousand BTU/hr, probably 1" is your best bet.

mattmia2

but depending on the resistance of the boiler it may require a dedicated circulator just for the boiler mostly depending on the heat exchanger design.

kinghoward

This WM boiler has a circulator in cabinet, there is a small circuit ( a spaced T branch a few feet long) that goes back to the "main" line and there is another circulator on that main line. Worked good for 5 years

mattmia2

that is piped primary-secondary.

hot_rod

Some of the Weils have a primary secondary loop built inside the cabinet. The ECO was one.