I have an old building with a boiler and the old steam radiators (most of which are disconnected). The boiler has not been used in 20 plus years. What would be a good low cost replacement system. Could I re-use the old boiler?

You'd be better off not to. A steam system can't be zoned, so will waste tremendous amounts of fuel at a time when it is becoming very expensive.

Insulate the house completely, so you aren't supporting an antique white elephant. Also, install a new zoned hot water system. These will cut the cost of heating to 1/3rd of the old uninsulated house with steam for the next lifetime.

http://www.heatpro.us/designtree/documents/tanklesssys.htm

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Thank you for your response. It is along the lines of what I had thought. I know this site/forum is for homes, but my "project" is a large building (3 floors - basement, main, upper) and about 10K square feet. Do you think that a radiant floor system would be effective in a large building? How much space can you heat with a "tankles" boiler/heater? Thank you in advance.

A building insulated to 1990 or newer standards requires about 25,000 btuh per 1000 square feet.

Commercial buildings are unique heating cases, as large occupancies and lighting loads can supply all the heat needed, thus requiring backup heat for low occupancy.

You'd do best to hire an energy engineer to give estimates of which heating systems to use with expected bills. Utility companies often supply such info to prospective owners.

Radiant heat can supply the heat as well as others. A caveat is that radiant heat doesn't include fresh air exchange required for occupancy codes.

www.heatpro.us energy businessmen's knowledge

Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.