Do radiator covers in the house make the radiators more or less efficient?

[stpauler]

Having just finished my first woodworking project, I’m trying to decide on what to do next. Having looked at our relatively ugly radiators in our wonderful craftsman house, I thought this would be a good next project…except I can’t tell if they’re just for aesthetics, would improve our heating bill or make it worse.

Treehugger says:

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

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.

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 maximise radiation. Anything that blocks air flow reduces their efficiency.

This says:

Efficiency

Some people say you are preventing a radiator from transmitting heat to the air and surrounding area when you cover it. Other people say that because the hot air coming off the radiator goes straight up, a bare radiator is an ineffective way to heat your house.

Radiators do circulate some hot air around the room, but the majority of the heat is transmitted via radiation. Because most radiators are on the outside walls of a house, a lot of the energy is wasted warming an exterior wall. Many sites suggest insulating the backside of the radiator with a foil insulation to reflect the radiant heat back into the room. This is a smart thing to do even if you are not going to cover your radiators. If you plan to use your radiator cover as a shelf, some people suggest lining the underside of the cover’s top with this insulation to keep it cool.

Telegraph UK says:

AIf properly designed, with large air gaps at high and low level, a radiator cover should not interfere with the heat transfer from the radiator to the room, as there will be a flue effect of air being drawn through it. But a poorly designed or DIY radiator cover, relying only on the perforations in a sheet of decorative MDF or hardboard, might not work so well.

And Chicago Tribune gives the sort of non-answer:

There’s also the notion that the covers make the radiators more energy efficient by concentrating or directing the warm air produced by the radiators. This, however, is untrue. Radiator covers do one thing: cover up radiators.

The flat tops of the cover also allow homeowners to use the tops of the radiators as bookshelves. The problem is that the covers can block heat generated by the radiators. That forces the boiler to work a little harder to produce the heat needed to get the room to the temperature set by the thermostat, which raises your natural gas bill.

The energy efficiency question here is how much do radiator covers cost as far as additional energy dollars? That depends on the size of your home, the number of radiators and how many are covered.

You also have to take in consideration how energy efficient your home is. Then you have to decide if the aesthetics of the radiator covers are worth the added expense.

Aggregating the info, it seems that radiator covers block more heat than what it good, but having a reflector on the back would help. So, in other words, they are ineffecient. But is that the right answer?

[Cheesesteak]

Given that they are passive, I don’t think you can manage anything better than par with an uncovered radiator. An uncovered radiator will radiate in all directions, and will enjoy convection as well.

I think that most likely they are less efficient overall. One thing to consider is that the space inside the radiator cover is going to be much hotter than without a cover. That hot air will reduce the rate of heat transfer from radiator to air, so more of the heat energy stays inside the radiator. The radiator won’t actually get any hotter, because the steam/water is at a fixed temperature, it will just transmit less heat to your room.

I think that one day I will install grates in the tops of my radiator covers to enhance the flue effect. They may be less efficient, but I don’t like the looks of a bare radiator.

[phreesh]

Anecdotally, I have noticed that the air beneath a radiator cover is much hotter than the air right next to an uncovered radiator. I would surmise that this means that the heated air has a more difficult time getting to the rest of the room in a covered radiator and is therefore less efficient.

[ZenBeam]

I’ve never had a radiator like the one in the OP, but we have baseboard hot water heat here at work. Those work primarily by convection, not by radiation. Cutting off the air passage at the top of them cuts the heat they produce way back.

If you make covers, and make sure to allow for good vertical airflow, they should work well. I’m going to guess that the covers that phreesh describes block that airflow, and just have vents on the front.

Could you make a design like this I “drew” n cross-section, with an angled opening at the top to allow good airflow. That gives you a shelf on top. Optional whether the front cover is solid wood or has holes. Without the holes might work better, since you’d have a good chimney effect going.

|
|Wall
|
|   ____Cover
|  |   /
|  | /
|  |/
|  |    |
|  |    |
|  |    |
|  |    |
|  |    |
|  |    |
|  |    |
|  |    |
|  |    |
|  |
|  |
|  |

Whatever designs you consider, you could make a mock-up using corrugated cardboard first, to verify that it still works to heat the room. (Presumably these are no where near hot enough to be a fire hazard.)

[stpauler]

Here’s a picture of the “offending” radiator in the dining room. The thought was to do something similar to the mission/prairie style here.

It sounds like that style definitely won’t work without at least making grates or similar bars on the top to let the heat rise and that the backside is the most important part anyways.

[ZenBeam]

@stpauler

Here’s a picture of the “offending” radiator in the dining room. The thought was to do something similar to the mission/prairie style here.

It sounds like that style definitely won’t work without at least making grates or similar bars on the top to let the heat rise and that the backside is the most important part anyways.

Thinking outside the box (;)) if you made the top be hinged, you could have it open when heating, but close the lid during the warm part of the year. Another option might be to add small quiet fans, like they use in computers, to increase airflow past the radiator.

Honestly, though, I think the radiator looks nice as part of the room decor. I’d be worried that a cover would look worse. It would have to be taller than the radiator, and would interfere with the look of the bottom of the window (IMHO). A backing that is behind it to reflect heat from the wall, painted the same green color to hide it, might be the best approach.

[Joey_P]

I don’t like the Chicago Trib answer. If the radiator doesn’t give up all of it’s heat, the hot water will return to the boiler and be recirculated. The boiler may have to fire a little extra to make up for any heat loss in the walls, but that’s very little. It’s not like the pipes are running down the exterior of the house on the way back down and releasing any unused heat to the outside.

Also, if you make the cover sturdy enough you can effectively add a lot more seating to your room. Or, if that’s a dining room, just make it higher and use it as a buffet. If it extends a few feet above the radiator it’ll be like it’s not there (as far as the radiator is concerned). Just space the slats out a bit further, don’t put any on the back and leave them a bit higher off the ground so you have plenty of airflow. The one you linked to does seem a bit insulating.

[ZenBeam]

@ZenBeam

if you made the top be hinged, you could have it open when heating, but close the lid during the warm part of the year.

Or you could make the angled part in the picture I made be hinged, so it would be angled open for heating, and closed to provide another shelf when it’s warm. You’d always have the top surface

[Northern_Piper]

There were radiator covers on the radiators in the house Mrs Piper and I bought. We eventually decided to get rid of them because we didn’t like the looks.

As we ripped them out, the rooms got progressively hotter, as the hot air trapped inside the covers was released.

I concluded that the covers were significantly interfering with the free flow of hot air.

[kanicbird]

It looks like you painted your radiator which does lower it’s efficiency.

I can see a cover helping baseboards by creating a chimney effect, but I don’t think that would work well with they radiator you are using.