To cover or not to cover; that is the radiator question...

brad_23

Reading through these forums regarding radiator covers, it seems far from easy to determine how radiators affect heat output or efficiency of a radiator.

For example, while there are those old diagrams showing that a fully enclosed radiator decreases its efficiency by up to around 30% (if I understand that correctly), which would lead you to believe that removing radiator covers would make it more efficient, there is also issues with oversized radiators and how putting covers on them could ironically make the system less efficient – something about too much condensate being produced?

As a homeowner with a 1922 house with a one-pipe steam boiler my concerns are to make sure the radiators are efficient so that 1) My house is heating well and 2) I’m being efficient and not overspending to heat it.

My radiators have covers, they are old, but there is no way of telling when they were first used in my house, so it’s unclear if they are “supposed” to be there. And that’s my question: how do I go about figuring out if my radiators should have covers? I have a friend who believes the issue is simple: a cover traps the heat, so removing the cover will allow the heat to better enter the room and will make the radiator more efficient. Except, I’ve read this is not the case for an oversized radiator where an uncovered radiator is actually inefficient because it loses heat too fast??

I guess another question is, what are radiator covers really doing and how do they improve/hinder convection/conduction? Are they beneficial? Most importantly, how do you determine when you should cover or not cover?

Brad White_203

Time for a Brad to Brad chat

"Most" covers over cast iron radiation restrict the heating effect, with certain exceptions.

The first casualty is radiant heating, that "line of sight" infra-red radiation that is obviously blocked.

The next is conduction, the fact that the now-enclosed radiator has a higher ambient. Your "240 BTUH per EDR" is based on a presumed 70F room. If your enclosure is now 90 degrees, 110, 120 degrees, your output of course will be less.

One exception to the rule is where the bottom face is open and the top is open or grilled to allow a "chimney effect". This promotes greater airflow across the radiator and increases output by 5 to 10 percent over and above what is not radiated.

If you tend to have steam radiators which are over-sized, proper application of enclosures can bring them into line with your actual heating needs. This is kind of like navigating by where you have been, but can be done. Personally a system properly vented and controlled without covers is a good baseline. Perhaps a second floor with a well-insulated attic has created a condition of radiator over-sizing, so that second floor might benefit from covers.

So often folks who make and sell covers cite them as "increasing efficiency", which makes me shake my head.

If you remove the covers, what happens in your case?

RonABC

I have a one-pipe steam heating system in a house I recently bought, and all of the radiators have nice metal radiator covers.

I don't know about how the radiator covers affect the heating efficiency, but I will be renting the property out to others and I don't want anyone getting scalded by leaning directly against the steam radiators. So, for me, the radiator covers are a necessary safety feature. I am also insulating the vertical pipes that go up to the next floor for the same reason.

brad_23

OK, now were talking...

"The next is conduction, the fact that the now-enclosed radiator has a higher ambient. Your '240 BTUH per EDR' is based on a presumed 70F room. If your enclosure is now 90 degrees, 110, 120 degrees, your output of course will be less."

Isn't this also saying that there is less radiant heat? And, when you speak of output, do you just mean output from the radiator or does that have something to do with how the work the boiler is doing?

In my situation, I have three floors. Two summers ago the third floor was completely remodeled and majorly insulated. Also at the time, I replaced all radiator vents with brand new vents. They had Gortons with various sizes, but I replaced them with all Hoffmans of the same size, which I'm thinking might have been a bad idea? This fall I replaced the main vent (using help I found here on the board) and that has made an incredible difference -- the system is nearly silent and seems to heat comparatively quicker.

So, now with a tight third floor I have a second floor that is a few degrees cooler than the first floor, which I think you would assume would be just the opposite. My reaction is to assume that the covers stay on the warmer first floor, and come of the second floor. I barely need the third floor radiators, and only have one of three open.

Without removing them entirely, I first opened the lids of the radiators on the second floor. I don't think anything measurable happened. On its face, it seems logical that the rooms would be warmer after just removing the covers entirely, but then I read about over-sized boilers and too much condensate -- is it possible that the radiator could give off heat too quickly? Then, don't you end up with a situation where covered radiators retain heat and continue to radiate slowly and uncovered radiators quickly give up all their heat and then the room gets cold before the covered radiator rooms -- is this a concern?

Brad White_203

To your questions/points in order:

Radiant heat is just that, line of sight. It is not the same as conduction (contact with a surface, not really applicable here), nor is it convection, (the movement of air in this case, warmed from dense to less dense and which carries heat into the space).

A typical cast iron radiator open to a space will have a radiant output of about 30-35% and the remainder convective, as I recall. (I have charts to say just what it is, but for discussion, this is a ballpark. Others should feel free to interject here as always!)

The effect on what the boiler is doing is about proportional to that. In other words, the steam is not going to condense at as great a rate if the radiator is "enclosed in a box". Thus the boiler becomes over-sized but also maintains pressure longer between cycles. If the space heats and spaces heat evenly, I can say that you are doing OK.

As for your recent work, sure, I like Gortons, nothing against others, but if you are heating quickly and silently, who is anyone to argue? You have done much!

Now, the second floor being cooler than the first... yes, counter-intuitive but it really all gets down to this: What is the heat loss of each space and what is the output potential of the radiators in each space?

Toss in any other factors such as covers, venting rate, solar gains, thermostat placement, over-radiation on the more comfortable floors and, well, who knows? But you have to reconcile heat loss to radiator potential if you want to know.

Removing just the tops (that you can do this is great!) will increase and promote convection. More airflow concentrated than if open to the space by itself. That old chimney effect.. Baseboard radiation benefits from enclosures and is one reason that is is as effective as it is. It just does not radiate as well you see, by comparison.

The notion of any radiator giving off heat too quickly- that would show up in an over-heated room. Your space comfort is your best indicator, no matter what you calculate. As for retained heat, the covers have little mass compared to the radiator. I would not concern myself too much. Sure, a little more mass but I cannot see a huge time difference in cool-down time, maybe a five minute difference and probably not even that. Cast iron rocks, no?

Al Roethlisberger

My ca 1920s have been covered since day one


I really can't answer your question(s) definitively, but I can say that my hot water radiators have had the typical stamped steel covers since they were installed ca 1929.

Al

McKern_2

If the front of the radiator is a decorative metal grill, is this considered an "open face"?

Thanks

mark ransley

Heat is held in a bit by covers,if the radiator is on an exterior wall you just heat up that wall more and loose it to the outside. Take them off exterior walls and get 1 or 2" R 14.4 foil faced both sides Polyisocuanurate foamboard, at HD-Menards. Foil reflects radiant inside, R 7.2 " is the highest R value per inch you can get in building insulation. Is house old, yes im sure it is and walls may be less than R7" now. Cauld foamboard back edges very well before screwint it on or condensation and mold will grow behind the foamboard. If second floor is colder balance it with different vents, adjustable if you own, non adjustable Gorton if you rent, Gorton have 5 ranges. The Blue and Pink foamboard are good but only R5" and no foil radiant barrier.

Charlie from wmass

Well they only lean on them once if they are smart twice if not so smart, three times means they need help and a padded room. The other issue with covers I have seen is dirt. when the cover is clean the homeowner is happy but they do not see all the dust and dirt and what have you that has gathered over the years. Some radiators, actually called convectors were made for and used covers. This is different from the after market covers sold through the hardware stores and such places. I vote tag sale them or recycle them.

Brad White_191

By my definition

I would say so. The older details depicting the de-rating factors indicated a grille, at least in section.

No telling what free area and such, though.