Heating a suite with baseboard radiators

“Hot air rises and warm air rises slower”

Function and fixes

The majority of 4-storey wood frame apartments have copper tube baseboard radiators for heating. This month I will explain how they work and simple things to watch to help reduce complaints and service calls.

The standard baseboard radiator is made of ¾" copper tube with a continuous row of aluminum fins pressed on. This tube and fin assembly sits inside a metal cabinet. It is important to note this cabinet has an opening on the top and at floor level. The hot water from the boiler flows through the copper tubing and heats up the aluminum fins to create air flow in the room. There is evidence of this air flow from streaks of dust seen on some walls directly above the radiator cabinets.

Imagine the suite as a box and the heating air flow as a rotating circle within the box. In order for the air to flow, a few conditions need to exist. The radiator must be at least 140° F. The opening at floor level of the radiator cabinet must be clear. The following is an example of how most air circulation problems start: A large couch with a floor length skirt sits in front of the largest portion of the radiator. The tenant puts a 2" shag rug up against the bottom of the radiator. The aluminum fins are plugged with dust. The top opening often has a manually adjustable damper. Most of these dampers are hard to open and many are left closed or half-open at best.

All of these conditions will prevent the cool air from sliding across the floor and back to the radiator. This lack of cool air flow across the radiator fins inhibits the amount of hot air created to rise up the wall and across the ceiling. The suite needs both water flow through the radiator tube and a clear path to allow air flow in the room.

A clear path for air flow becomes even more important in buildings with energy management systems. When the water temperature flowing through the radiator is reduced in warmer weather, the ability to create air flow slows down. Hot air rises and warm air rises slower.

One foot of standard copper radiator will produce 550 btu/hr at a water temperature of 180° F. This same foot of radiator will produce 290 btu/hr at 140° F. It is common to see a 140° F water temperature in the radiators during warmer weather. For example, on a cold winter’s day a one-bedroom suite will need about 10,000 btu/hr of heat and 180° F water flowing through the radiator. This means 18 feet of radiator is required. On a warm day with 140° F flowing through the radiator the same 18 feet will produce 5,220 btu/hr of heat.

In summary, the radiator can be red hot but if there is no path for the circular movement of air, the tenant will be cold.