Can I improve convection?

Tezak · February 17

The previous owner put these cabinets over radiators in the main living spaces of our two unit building. I know that cabinets aren’t optimal but I’m keeping them a few reasons:

underlying radiators need to be cleaned up and painted and I don’t want to do that now
Tenants usually find the covers attractive
They provide a nice shelf

I want to increase convection without drilling the tops. My idea right now is to remove the hinge pins and raise the lids up on blocks of wood so there’s a 1 inch gap all around. Was thinking I’d glue little blocks in the four corners. They don’t look as nice this way but hoping to reduce my gas bills a bit!

I just wanted to see what you all think about this solution? Any other modifications I should consider?

Tezak · February 17

I’ve been thinking about this design a bit but I worry about covering that much of the front grill. Would it actually increase convection enough to warrant blocking radiation?

Jamie Hall · February 17

Lifting the top like that will help — possibly quite a bit, depending on how completely the radiator fills the space behind the cabinet. I wouldn't block the front grille…

hot_rod · February 17

I think there is a trade off with covers? You limit the heat emitted by radiation when you cover a portion of the radiator surface. Maybe the covers increase convection? If you look at copper fin tube the cover design allows cooler air in the bottom, the front cover forces air currents across the fins and warmed air comes out the top damper.

With an expanded metal cover like that I don't think you are getting the best convection output? The drawing you have indicates that also. It would be easy enough to take a piece of cardboard and cover the middle portion and see how it changes.

If more heat output is the goal, I wonder that removing those covers would provide that? The radiant heat transfer is a nicer "feeling" heat in my mind. Convection tends to move dust along with heat :)

Seems like a shelf could be built without needing the enclosure. Clean the radiator until you can repaint it?

mattmia2 · February 17

Raising the top will make those radiators output more heat but i don't know that it will do much for your gas bill.

Big Ed_4 · February 17

If the grill mesh is made with iron . You can cut up a magnetic sheet and experiment with needed out put …

Does the room need more input to make comfortable ? A cover could slow the output with no loss of energy …

Tezak · February 17

This sunroom tends to be a little colder because of all the windows but honestly not by much. The house is mostly warm and well balanced. My main goal is to get things up to temperature faster hoping to reduce boiler runtimes.

Long Beach Ed · February 17

I don't believe you will see any improvement by modifying those covers. Spend your efforts elsewhere like improving venting and sealing the heating envelope.

Jamie Hall · February 17

https://forum.heatinghelp.com/discussion/comment/1843168#Comment_1843168

Um. "Up to temperature faster"? This implies you are using a setback? Whether that is true or not, you can only raise the temperature as fast as the boiler can supply heat and the radiation emit the heat. If the boiler isn't cycling while you are getting things up to temperature, just increasing the radiation isn't going to make a difference. The boiler — the engine, if you will — is giving you all it's got.

EdTheHeaterMan · February 17

I'm not sure that the Math adds up. The heat that is not emitted as a result of the covers returns to the boiler. That makes the return water a little warmer, so the boiler reaches the limit temperature a minute sooner. As a result the burner stops and the circulator pump keeps running to dissipate that “free” heat so the boiler temperature can drop. Your idea that the thermostat will take longer to satisfy with the covers on the radiators may be correct but it does not necessarily mean that the burner is running the entire time that thermostat is calling for heat. The burner may be off by the limit switch for more time as a result of the covers. So the net result may or may not save you on your gas bill. If it does it will not be enough to notice in dollars, maybe only in pennies.

And as we all know a penny costs 2 cents to make so you may actually be spending more money with a couple of cents in lower usage.

DCContrarian · February 17

https://forum.heatinghelp.com/discussion/comment/1843168#Comment_1843168

Effectively, the covers make the radiators smaller, improving convection would make them bigger. Changing the size of the radiators doesn't affect system efficiency. The only reason to do it would be if the radiators are undersized with the covers and can't maintain temperature on the coldest days.

AdmiralYoda · February 17

I'd vote to remove the cover altogether! And if you want, install a shelf above the radiator for storage.

Covers have two purposes in my opinion. To keep kids from touching hot radiators and to dampen/disperse the heat out of the radiator.

You'll feel the heat radiating from it faster but it isn't going to add any additional btu's to the room. It might just "feel" hotter, quicker.

Big Ed_4 · February 17

Women like to use radiator covers…Guys would prefer to paint them :)

pecmsg · February 17

in my house the radiator by the stairs going up, when at single digits and the NE Wind blows. that top cover gets removed and it makes the difference on the 2nd floor

Tezak · February 17

I think I’m more confused than when I started 😂 I may just have to experiment a bit. I’ve read all range of opinions on this topic on the forum. Many claiming that they kill efficiency, others saying they have no effect at all, most saying get rid of them (why if there’s minimal effect beyond aesthetics?).

Tezak · February 17

it’s clear when I tape a piece of paper near the gap, comparing the original and modified version, the modified is moving much more air.

pecmsg · February 17

simply

Covering any emitter will reduce the output. If the heat doesn’t go to the room it winds up back in the boiler, + or - a small %.

As long as the rooms not cold there’s no reason to change it.

Tezak · February 17

@pecmsg thanks that actually helps a lot. I may keep pursuing this and see if I can boost comfort if not savings (not giving up that easy though). Keeps me out of trouble at the very least.

Big Ed_4 · February 17

Adjusting the inside humidity would improve the comfort in the home …. Bowls of water sitting on the top adds moisture during the winter months …

Tezak · February 17

these covers used to have trays for that. With them all full it only increased the humidity about 5% unfortunately

EdTheHeaterMan · February 18

https://forum.heatinghelp.com/discussion/comment/1843251#Comment_1843251

5% more humid is better than 5% dryer air. How long did it take to evaporate that water?

As far as why some people decided to cover the radiators is concerned, you need to understand why most radiators are oversized in the first place.. Even though the story is about steam boilers, the same holds true for oversized gravity hot water radiators. After the health scare issues were over, the Heating Industry still used these oversized specifications for a lot of years after. Kind of like seeing some people still wearing face masks while alone driving their car 4 years after Covid 19.

Now in the 1940s and 1950s the big stink about "Fresh Air Movement" was over and we had all these oversized heaters and radiators and the government published studies about the effect of radiator covers and what color to paint radiators in order to reduce the output of oversized radiators in many homes and apartments. There are many apartments today with steam radiators that make the room too hot. The only recourse for the tenant is to open the window in order to make the room a little more bearable.

If your home is comfortable and balanced with the covers in place, then adjusting that balance is not going to get you any measurable savings on the gas usage, but it may end up setting your comfort out of balance. So don't do anything that is so permanent that you can not reverse it to get yourself back to the way things are now.

Tezak · February 18

if anyone’s interested, today I tested two heating cycles: one with the covers open about 2” similar to the photo, another with them closed as normal. With them open the boiler ran for almost exactly 30 min and with them closed it ran for right around 35 min. Comfortable levels were the same. Seems like it I could see decent savings over the course of a season. It’s around 5 degrees here so the pipes were hot for both cycles.

Tezak · February 18

or do the extra BTUs mean the building will stay warm longer and there will be more time between cycles?

hot_rod · February 18

the building and the temperature around it is what dictates the heating cost. Changing that radiator configuration will probably do little to nothing to save fuel costs.

Look for places to upgrade the building itself. Insulation, weatherstrip, window shades.

Have an energy audit done to find leaks in the building, an infrared camera scan can show a lot of heat loss areas.

DCContrarian · February 18

https://forum.heatinghelp.com/discussion/comment/1843284#Comment_1843284

This.

Tezak · February 18

I really appreciate the feedback everybody. I’ll probably not move forward with this as it seems like the overwhelming opinion is that it’s not worth it 🫡

Dave in QCA · February 18

I have been reading other posts over the years that speak to the fact that most radiators are oversized and that rooms tend to have more radiation than required. This is offset by the radiators rarely ever heating fulling across because the thermostat is satrisfied.

In your case, you have effectively decrease the "effective" size of your radiators a bit. Now much, I don't really know but I would guess about 10% give or take. Remember that the reduced output form the radiator is reflected in reduced steam condenstion and therefore a reduced load on the boiler. Personally, I like radiators better than radiator covers and when we bought the house we set 16 relatively new covers out by the curb. But, that was only because of a matter of taste. Unless your covers so greatly diminish the output of your radiator I would not spend any time worrying about it. Instead, as others of said, focus on things that produce a measureable effect. Weather stripping, storm windows, weatherstripping you wooden windows if you still have them, vinyl replacements are a bad return on investment given their short life and nonreparable nature. Attic insulation, basement foundation cracks, and so forth.

danmayer175 · February 18

This page is from a 1930's edition of Architectural Graphic Standards, indicating the reduction in performance for each configuration of radiator enclosure. Not clear how they came up with these numbers, but for what it's worth:

HeatingHelp.com · February 19

Here is some more info:

https://heatinghelp.com/systems-help-center/radiator-covers/

dabrakeman · February 19

https://forum.heatinghelp.com/discussion/comment/1843542#Comment_1843542

I was going to say. This is all in Dan's Every Darn Radiator book.

dabrakeman · February 19

There are differences in the numbers between what is shown in the HeatingHelp link vs Dan's E.D.R vs Architectural Graphics Standards but all agree that best for your purpose of increasing edr is the configuration with barrier in front of the radiator with no top. With a top best is with holes in the top and the barrier in front. If no holes in top raise the top with the barrier still in the front and effect will be a wash.

Tezak · February 28

I’ve never seen a cover with the barrier front. Does anyone have photos or examples irl? I’m just curious about a real implementation.

Can I improve convection?

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