Converting Steam System Back To Hot Water

And, @knudsluk , have you pressure-tested everything to make sure it will hold 30# pressure? If not, you might be in for a nasty surprise………..

You really need to start at the beginning.

Manual "J" Heat load / loss calculation, whole house and room by room.

Size the boiler to the whole house.

The radiators get sized to the room losses.

Now you can decide on pipe sizes!

The pipe size to each radiator when using a circulator can be 1/2". That size pipe can move about 15000 BTU at a flow rate of 1.5 GPM with a 20° ∆T. I don't believe that any of your radiators will be larger than 15000 BTU.

What size boiler you are going to use depends on the heat loss of the building, but you don't need anything larger than what your connected radiation will be able to use.  (eg. a 200,000 NET BTUh boiler will not be efficient if it is connected to only 50,000 BTUs of radiator.)  That will be oversized by 400%.

You should get a manual J heat loss or Hydronics Institute Form 1540WH load calculation completed yourself or by someone else so you din't select a boiler that is way oversized.

This booklet may help you with your pipe size selection Zoning Made Easy or this booklet Idronics vol. 12 to get basic information about your project.

Jamie is right about your heating system as top fed steam is simple own and use.

You will be better off economically using top fed steam to heat this place with a modern steamer and a double drop header to make dry steam. You need a steam licensed plumber to help you with this.

If planning to finish basement because you need more space then cut to the chase and spend some $ . Have a heat lose performed and instead of trying to re use and spend extra on labor just cut to the big chase and remove it all and toss . Have a real hydronic expert perform a room by room heat lose to size both the boiler and the heat emitters . They can pipe it all so you can have all the basement space and head room that you want . Personally i would size for low temps 130/140 max using panel rads w trv and in the long run install a cast iron boiler ( chimney vented)w return temp protection ,you could go w a mod con boiler and forget the return water protection but a few years the yearly maintenance will chew up the mod con savings and a shorter life span then a cast iron boiler . The reason i say low temp is if all goes down hill w gas/oil fuel and where stuck in electric if sized for low enough temp a conversion to air to water heat pump might work and the ultimate answer is it all depends . Even if you do the conversion remember to add a magnetic dirt separator and possibly a wye strainer for sediment issue . personally i would show zero interest in trying to reuse any of the steam piping there's just too much liability and possibly unaccountable time for issue which cannot be seen . I used to be asked about these types of job and i usually pass being there just unrealistic and at a later date some one is left trying to deal w a issue that some one else has created and i sure dont want it to be me .

My personal view is older steam systems w zero insulation and a lack of maintenance and issues always require alot of work and some issues will cost ! Everything has a life span and so does a system at some point things have to be updated and to put it in perspective most home kitchen far exceeds the total cost of a completely update heating system but no one see the heating system but all looking at the big $ put in kitchens and dont forget baths . Some times priority of non required far exceed the costs of the mech of a home very funny stuff .

In my dads words big house big bills, old houses bigger bills plain and simple

peace and good luck clammy

i don't understand the bathroom renovation. you are taking this tile set in mud and cast iron and china fixtures that will last 100 years that was built by skilled craftspeople and you're replacing it with this least material they can get away with stuff that will be moldy and falling apart in 20 years. sure, replace some of the plumbing and electrical but what you already have is something you're unwilling to pay for in the replacement.

a lot has changed about the structure since 1908. assuming the radiators from then are the right size for a modern system is a mistake.

It's entirely possible that the reason the building was converted and repiped was that the existing system wasn't satisfactory.

They didn't. They came out around 1938 or so.