CGA Temperature

it depends on the amount of hot water baseboard there is in the building compared to the actual heat loss of the building. Any specification sheet on a particular model of baseboard heating units will give you the heating capacity per linear foot based on the average water temperature of the water in the baseboard radiator. If you design on a 160°F water temperature there will be about 20% more radiator per room. If you design for 180° average temperature, then you will save $$$ on material cost, at the expense of operating at a higher temperature. operating at a higher temperature will cost more in energy consumption. If you are designing from scratch, and you give your customer the choice of more radiators and lower operating costs, then they may be interested in a higher price for more radiators.

If you are replacing a boiler on an existing radiator system and you don't know the design criteria then you can try a lower temperature limit setting, but be prepared to return on a extremely cold day to increase the limit temperature. Remember that you will probably be dealing with frozen pipes for other customers that day in the future. Just leave it at 180° limit, and forget it.

Generally, a supply temperature of 180°F is only need at design conditions. Lower temperature can and are used during warmer weather. Outdoor resets 256 - tekmar. With cast iron boilers 130° return temp is about minimum to prevent condensing in the exhaust gases.

the not going so low that the boiler condenses is important. without doing some math or measurements you probably don't want to go below 150f.

lower boiler temps will make it run longer cycles and be more even. It is unlikely to have a significant effect on efficiency. not oversizing the boiler, sizing it to the heat loss of the structure is what will keep it from cycling or getting hotter than it needs to.

though it is possibly if they designed for 170 awt and got the sizing of the emitters pretty close to the actual heat loss, it is rather unlikely that 150 f vs 180f swt is going to make the difference between if it heats adequately at design conditions or not but lowering it 30 f degrees also probably has little benefit with a cast iron boiler and fin tube baseboard.

with cast iron radiators it could make a big difference because once you heat up all that mass of cast iron and water it radiates heat for a long time after and if there is too much heat in that system it could cause overheating after the call ends.

idronics is good to read to understand this:

This book is also good(you don't necessarily need the current edition, you can get a used copy of and older edition):