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radiator covers

Enclosure manufacturers seem to love to pull out <I>portions</I> of studies that sometimes show benefit while ignoring the major portions that show a significant reduction...

The University of Illinois studies mentioned are likely those from the mid to late 1920s!

Some VERY important things to note from those tests:

1) This was for STEAM radiators (216.5°F) steam placed directly underneath windows (with storms).

2) The outside air temp was quite cold, approx. 3-4°F below zero.

3) Exterior walls were well-constructed frame. Solid sheathing and clapboard. NO INSULATION!

3) There was a fan directly blowing against the window.


One of the University of Illinois studies found agreement with other studies that the ONLY enclosure that could actually increase output was not really an enclosure. It was a screen placed 2½" from the front of the radiator with NO TOP and an open slot at the bottom. The higher the screen extended beyond the top of the radiator, the more output. This is essentially making a modified chimney that increases air velocity right up to the ceiling.

By the way, the ideal placement for sides and ends of enclosures was found to be EXACTLY 2½" away from the radiator.

The "typical" manufactured covers that I have seen will typically reduce the output by 15-20% for high radiators and 25-45% for low radiators! A curved deflector at the top rear helps a touch, reducing the loss by 2.5 - 5%


The statement that some enclosures can increase the air temp at the "living zone" by <I>up to</I> 4½° is substantially true. The air temp at the ceiling was also reduced significantly. The temperature at the "breathing level" was essentially unchanged. That "proper" enclosure was VERY specific. It surrounded ALL FOUR SIDES of the radiator (including the back). The top was solid, the front screened and there was an air slot at the bottom.



With hot water radiators at 158°F average temperature, the output change caused by enclosures was essentially the same as steam. However, I cannot find the affect on air circulation using that "proper" enclosure.


My best advice is to NOT cover cast iron radiators. As you mention, you immediately turn them into a convector and much of the radiant output is lost. If you happen to be overwhelmed by the radiant output of some radiator (huge steam rad by a door for instance), use the old-timer's trick of painting it with aluminum-based paint. This will reduce the emissivity considerably and there will be less radiation.

In the case of hot water radiators it seems particularly unwise to cover them. Insulation and the general old-time oversizing frequently have rads operating at quite low temperatures. By keeping them uncovered you get the highest proportion of radiation and the lower the temp required to maintain the space, the higher that proportion of radiation. Cover them and the radiator will have to run warmer to produce the same output. If the rads happen to be on interior walls, ABSOLUTELY DO NOT COVER! As long as insulation and infiltration are reasonable, this is an ideal placement for extremely comfortable, very low temperature, high radiation operation.


  • D107
    D107 Member Posts: 1,860
    radiator covers

    My question is whether there is any kind of radiator cover made that will either improve a radiator's heating or at least not reduce heat. I have an old hot water heating system (with circulating pumps and cast iron radiators) and the covers I have just removed are wood, have no openable top, and have a grill in front. The following two companies claim they can help:

    (Barker Metalcraft) http://www.radiatorcover.com


    Barker Metalcraft says:
    Here are some commonly asked questions regarding radiator covers:

    Q: I've heard that radiator covers hold back heat. Is that true?

    A: No. In most situations, a properly designed radiator cover will actually improve the heat flow of a radiator. The University of Illinois conducted a study indicating that with a properly built radiator cover, the heat is directed out through the front - actually increasing the temperature in what they call the "living zone" (or lower part of your room) by about four and one half degrees.

    Q: So then what is a "properly designed" radiator cover?

    A: An effective radiator cover should have a reflective back to project the heat foreword, into the room. All Barker Metalcraft radiator covers include reflective backs at no extra charge.


    ARSCO Radiator Enclosures help conserve heat energy from the
    first day of use. A specially-engineered channel pattern directs heat
    through the grill, into the comfort zone and away from windows,
    walls and ceilings. As a result, a radiator’s heating ability is fully
    optimized, and heat losses are greatly reduced.

    ARSCO supplies schools, hospitals, hotels, offices and churches
    with quality radiator enclosures, specialty HVAC products and space-
    saving storage products. ARSCO products are custom to your needs
    and are designed to be functional and durable – and look great!

    ARSCO has a proud 72 year history of service to America’s leading
    school administrators, architects and commercial contractors!

    Perhaps to avoid spending a fortune on 4 metal covers, I could screw in a piece of sheet metal (or tack on foiled insulation)to the rear inside to reflect the heat out. I know in this case the ‘radiator’ becomes a convector. But before I do all this, are any of their claims true? Natural gas costs this year will skyrocket and I’d leave the radiators bare (and painted) if that would save me significant money.


  • Steamhead (in transit)
    If that were my house

    I'd junk the covers. Most of these things are so poorly designed that they seriously reduce the radiators' output- some by as much as 33%. They also collect dust as you have no doubt found out, and can hide leaks.

    If you're in a situation where you absolutely must use covers, cutting vent grilles in their tops will help a lot.

    Here are two links to check out:


  • Dave Stroman
    Dave Stroman Member Posts: 766

    Try this one.


    Dave in Denver

    There was an error rendering this rich post.

  • ScottMP
    ScottMP Member Posts: 5,884

    Those covers are the typical design that is So problematic. They retard air flow over the radiator which decreases output.

    I have had alot of customers with this problem. The room never heats, O.K. take off the covers and see what happens, Yes but I like the look, O.K. stay cold :)

    Here is the an oldie but goodie. I think this shows the best design for radiator covers.


    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Hitzkup
    Hitzkup Member Posts: 63
    radiator cover

    i just checked this link that showed up un the right with this post.

    how are those radiators suppose to heat if its 95% covered with 3/4" poplar?
  • Mike T., Swampeast MO

    At least they don't claim an increased output and the testimonials only comment on the appearance...

    Presuming that the bottom open slot is at least 2-3" and the top screen has at least the same amount of open area, and top & front are 2½" from the radiator, output is reduced by about 25% for high radiators and 33-40% for low radiators.
  • D107
    D107 Member Posts: 1,860
    radiator covers

    I'd like to thank all those who answered my question. What a great community of problem solvers. (My Dad was a mechanical engineer for 50 years, so I think I inherited some of my interest in this from him.)

    I did neglect to mention that these ground floor US radiators (from the 1920s) are in front of windows, are 20" high, 48-50" long and 9" deep, and about 2" from the wall which unfortunately has suffered water damage from outside (long before we arrived) with crumbling plaster, mildew etc. but is now dry.) Also one of the three radiators has a long couch in front of it.

    Sometimes these things become battles of aesthetics between husbands and wives; my wife purposely turns her head away to avoid looking at the now-exposed metal monsters which I'm happy to paint.

    I also think it humorous how the companies that make these covers find ways to convince you how their very expensive products enhance your home heating. I suppose a few of the designs might work under certain conditions--I do like the idea of the heat going to the liveable area instead of up to the ceiling, but in actuality does it take that long for the higher, hotter air to drop down a few feet? Maybe I should look into those new mahogany boiler covers......

    Thanks again,

  • Mike T., Swampeast MO

    Rads of that sort are literally called "window radiators".

    For a given amount of EDR (equivalence of direct radiation) they have the highest output of any cast iron, free-standing radiator. Output is higher because of the nature of convection. A rad twice as high won't have nearly twice the air speed or air temp at the top of the radiator. The low, broad, long profile maximizes the convective area.

    If the original installer knew his stuff, those rads would be slightly downsized compared to any high rads in the house.

    Note however that low rads are the most adversely affected by covers! 40% reduction is not uncommon. Those studies showing a better temp balance with some covers were done with tall radiators.

    Am not at all surprised that comfort increased when you removed the covers.

    Had those rads been INTENDED to be covered, the installer would have upsized them quite heavily.

This discussion has been closed.