The clay may radiate after the candles have gone out, but you're still talking about heating a room with candles, which is not a particularly great idea.

Radiators, cast iron baseboard water and even fin baseboard systems are all prone to freeze damage.Horizontal runs in the domestic hot water delivery system are also prone to freeze damage.Food in refrigerators and freezers with the electric turned off all particular smelly messes.

I suspect it is a boiler (probably with period cast iron radiators).

A hose clamp and a piece of old radiator hose.Don't make a bid deal out of it.

Cast iron radiators?

@Ben Wilson - If it is forced air the tenants usually pay, if I it radiator heat usually it is 1 system and you pay.  

I just purchased my first flip at sheriffs auction but there is extensive mold due to the radiator register pipes bursting over the winter cause no one left the heat on.

Radiators?

I'm only concerned about the possible radiation.

Steam is more annoying than hot water, ive found, due to pressure and recirculation issues, in addition to how hot the radiators actually can get vs hot water, where burning someone seems almost inevitable.