"Slim" radiators?

I would think you should be able to replace them. Is it ac and heat?

They can be replaced, the size of the radiator gets determined by the size of the room, many times you get much larger radiator installed than needed. If your windows are well weatherproofed you can easily downsize it, it may involve some plumbing work though.

Heat only. I've heard that replacing it can lead to loud "ping" issues. I'm guessing a good plumber can figure this out. Any plumber recs?

You need an expert on steam heating. These guys are on my short list: http://www.gatewayplumbing.com/index.html

I have been told that i would not be able to replace mine with a slim one because it was a one pipe system that required a radiator to tilt. Our building is from 1910 approx. The "experts" on this board make assumptions without knowing sufficient details.

Somewhere in this guy's excellent book he explains why early-20th-century buildings were over-radiatored: http://www.heatinghelp.com/products/Steam-Heating-Books/25/68/Lost-Art-Of-Steam-Heating

E.g., my LR originally had three short/wide radiators under window seats. A previous tenant removed two of them. The remaining is sufficient, with the room dropping into the 60's only when it's way below freezing outside.

The pretty, flat Runtal radiators you see in ads are for hot water, not steam. This outfit makes thin steam radiators for one- and two-pipe systems: http://steamradiators.com

They all need a slight tilt during installation, and none are DIY.

I agree with NWT, all of them need slight tilting so the water doesn't stay inside and you don't get that banging noise. You can get the same radiator that you have but slimmer with the same connections.
And yes, all those fancy, chrome radiators that you see are for water heating.

clsm,

I have a great plumber for you who is very reasonable. Email me at primerenovations@mac.com

SURE you can! just check the btu's levels the slim radiators have a lower heat output so you may want to account for that.
The new radiators can come in colors and they look great!

flarf's rec for Gateway was helpful. We got a quote to replace very large radiators in 2 bedrooms for $2500. We'd like to get a 2nd quote (for comparison sake) but are having trouble getting recommendations for other companies. Can anyone suggest another radiator specialist?

most master plumbers can do the job. did you ask Primer's plumber?

Are the radiator's included?

I would be happy to help

primerenovations@mac.com

primerenovationsnyc.com

Yes, the radiators are included - slim but ugly, which is fine since we'll be covering them. I'll email you, Primer. Thanks.

I would not recommend using anyone recommended by prime renovations- we just used them for a bathroom and kitchen renovation. Total nightmare- worst experience ever. And at the present moment I'm trying to fix the faucets in the bathroom bc the plumber installed the faucets on opposite sides! And after two days, not only were the faucets installed incorrectly, but our marble tile was damaged. It has been a week since this happened and I've still not had my complaint addressed my prime renovations. And this was only one of the problems- we have a laundry list. Save your money and peace of mind and learn to do it yourself.