Do Radiator Covers Save Energy or Waste It?

Over at the Old House Web, Amy Hayden wrote about Five Benefits to Using Radiator Covers. This has started a bit of a debate: Are rad covers useful or do they waste energy?

Hayden wrote, "Radiators are a good source of heat, but they also take up valuable square footage... By purchasing a radiator cover, you can reclaim the flat surface on top to display books, picture frames or hardy plants."

But there is a problem with rad covers.

Convection

They may be called radiators, but they should probably be called convectors, since the bulk of the heat that we get from a traditional rad is moved by convection. In convection, air warmed between the fins of the radiator rises to the ceiling and is pushed around the room in a circle.

Some warmth is transferred by direct radiation, but not all that much and not to the right place, namely throughout the room.

Reflective Backing

Hayden wrote, "Radiator covers with the proper backing can distribute heat more efficiently than an uncovered radiator. Instead of the heat going directly to the ceiling, the back allows it to be pushed into the living space."

It is true that radiators should have a proper reflective backing; I use foil-faced bubble wrap insulation; it reflects a little of the radiated heat that would have been absorbed by the wall back into the room and the radiator. But more heat would be lost by blocking the convection upward with a cover, particularly if it is holding books or plants; you want the heat to go to the ceiling, that is how the radiator convects heat.

Lost Heat

Radiator covers can be useful in older buildings designed after the flu epidemic of 1918. Then, as is the case now, health officials believed that fresh air was the way to avoid getting diseases and that people should sleep with open windows.

Dan Holohan writes in “The Lost Art of Steam Heating” that in New York City, the Board of Health ordered that windows should stay open all the time, and the radiators were designed to keep buildings warm on the coldest day of the year with the windows open. Now that people are not doing that, rad covers can reduce the effective heat of the radiator by about 30%.

Radiator Types and Covers

Some radiators, like copper finned modern rads, come with integral covers, often with dampers to adjust the convection; they, like steam rads, need covers because they are too hot to touch. But for a traditional cast iron rad that one finds in old houses, connected to a hydronic system, a cover isn't needed for safety. That being said, caution is still required.

In a recent post, Holohan noted that some radiators can get dangerously hot. He described a lawsuit where a child rolled off the bed and got stuck between the radiator and the bed and suffered serious burns. He concluded, “If I was a landlord, I would cover all the radiators in the apartments that had little ones living there. I’d also make sure the system was working as it’s supposed to work. It’s the right thing to do. It’s common sense.”

Radiators are designed to expose the maximum surface area to the air flowing by them so that it can rise up; that is why the fins are perpendicular to the wall instead of parallel, which would maximize radiation. Anything that blocks airflow reduces their efficiency.