The BTUH capacity IS going to change. It'll need to be a lot smaller, to not short cycle.
If you are changing the radiator output from 240 BTUH per square foot to 170 BTUH sq ft, the boiler will be considerably oversized.
Now, instead of a few gallons of water to heat up, you'll have "how much" water to heat up? Can the hangers support that extra water? Will the slower response time matter?
With the extra water, do you think the cost to run will go up or down?
The ones I converted worked fine and never short cycled. I just put a T after the flow valve and another T before the circulator with a full sized pipe going between and valve for adjustment.
The heat loss isn't going to change, and the btu capacity of the boiler isn't going to change.
He already said the boiler short cycles now.
there is a lot more involved when trying to convert along with what Noel has said already
You have rust in the system and rads that you will have to deal with asn all that water lossens it up and brings it back to the boiler. Your return lines even though are not leaking have a tendasie to weaken over the years and can they handle the pressure of a hot water system at 12 to 25 lbs.
when real pressure is app;ied to these lines the may burst and cuase major damage or personal harm
As i said steam is great heat and needs to be ajusted properly. As far as over heating or uneven this isnt all that true. Once the system is balanced and set up all rooms should be even and the stat should be able to mantain with out a problem. A short cycling boiler can be from many reasons. When was the last time it was serviced.
Adding a few rads to the rooms with no heat is your best option with this system. If you want hot water heat then your best option it the size the system and replace it all with new.
Like i also said if thier are no better options then Steam baseboard works well
humidifier can also be installed on your ac unit and the blower will circulate it.
I can add hangers to the main loops in the basement. But also worried about the heat output. 3-Bedrooms are 12x15 with 10-ft ceilings and one radiator each with EDR of 45 or so.
If the temp drops to 160 for water, the output drops to 7200BTU or 40BTU/SF. With the steam it's 60 BTU/SF.
I guessing the boiler would just run longer to keep up
The radiation puts out considerably LESS, and the boiler runs LONGER to keep up with the smaller load?
Umm, no. That's not the way it works. If you cut the load on the boiler, it works less.
The PUMP will run longer, the rooms might not heat, but the boiler itself will short cycle and run SHORTER cycles.