Cast iron radiators often grace an older home, providing warmth throughout the winter. Radiators come in two designs, either steam or hot water radiators. Steam radiators use condensed steam to heat the radiators and hot water radiators use hot water. If you are unsure which type of radiator you have, a quick examination of the radiator design will help you determine whether you have steam or water radiators.
Examine the construction of the radiator. Steam radiators often have nipple connectors that connect the sections across the bottom of the radiator only. Hot water radiators often have nipple connectors that connect the sections across the top and the bottom of the radiator. The extra connection points help hot water radiators circulate the hot water as effectively as steam circulates inside the radiator.
Look for the pipes that connect to the radiator. Both steam and hot water radiators may have one pipe connecting at the bottom of the radiator serving as both the inlet and outlet pipe. A hot water radiator most often has two pipes connecting to it -- one at the top and another at the bottom. The top pipe is for steam entering the radiator and the bottom pipe is for draining out the condensation. A steam radiator may less commonly have two pipes connecting to the radiator -- both at the bottom -- along with a large hand valve at each pipe.
Notice the temperature of the radiator when the boiler is full of hot water or steam. A steam-filled radiator usually becomes exceedingly hot from the steam, whereas a hot water radiator usually becomes warm, but not hot enough to burn at the touch.
Find the air vent. A steam radiator with one pipe will have its air vent on the side opposite the pipe, approximately halfway between the top and bottom of the radiator. A hot water radiator should have an air vent at the top on the opposite side of the inlet pipe.
Listen for operational noises from the radiators. As steam radiators fill with hot steam, you will often hear hissing as the steam emits from the air vents. Steam radiators often make loud clunking or banging sounds from the steam also.
Check the floor beneath the radiator. Often a wood floor beneath a steam radiator will appear warped due to damage from the steam. A steam radiator may not sit level on a floor for this reason.