using existing high temp baseboard with new condensing low temp boiler

jon4747

Any thoughts .

EBEBRATT-Ed

Condensing boilers get maximum efficiency when the return water temp is below 130F which is the temperature condensing starts at. You can achieve this with baseboard if you install enough of it. The difference in efficiency between high and low temp is probably 10% of your fuel bill all things being equal

jon4747

if operating in non condensing mode is there any problem with high stack temperature in pvc vent

hot_rod

Many of those older systems can operate at lower SWT for much of the heating season.

First a room by room load calculation
Then consult the manufacturers output data, see how you match up.

Pretty much all the quality mod con boilers have reset control built in to allow the SWT to modulate with outdoor temperature.

This journal has some ideas for lowering SWT, formulas, piping options, etc.

https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf

Dave H_2

Heck ya!.

I moved into a new to me 40 year old home with standard fintube and the original cast iron boiler.

I replaced the boiler with a condensing unit, did the heat loss and compared it to the radiation and found that the hottest water temp I needed on a design day was 155F. Used a Delta T circ and had that system condensing almost the entire winter.

The bottom end of the reset curve I set for 125F, any colder than that, it was hard to get much output out of the BB.

Dave H.