Radiator Covers - Leave them or Take them OUT?

jp_2

efficiency word play

mike,

heres my problem: you said something like 'covering rads reduces output.'

In all aspects using the word 'efficiency' I've seen, altering the final output, with a constant input effects effectiveness or efficiency.

the discussion is revolving around the effects of heating the house.

i'd like to know where covers help? but showing a poorly designed system where covers improved is not a fair example in my option. got any examples with some numbers to show how and why covers would benefit?

since I do not know of this radiator "law" you speak of I really can't comment on it.

added: for this discussion to fall into the "ideal" realm is not really useful. especially since you always scream for 'real world' results.

jp_2

cricket

you are telling me then the piping systems in average old house have ZERO heat losses ?

Or ALL heat lost within the walls and basements are 100% useful? even those pipes so close to outside walls that tstat set back can cause freezing?

Is the moon also made of cheese? please tell me more....

Al Corelli_2

Repeat

Of those 1881 children, haw many have been treated TWICE for touching a radiator?

Shouldn't the parents of these kids teach them that dangerous things in their life may not be "magically" insulated from them? Or, should people grow up, in a haze of false security, bumping into walls, drifting into vehicle traffic, and electrocuting or drowning themselves with common home appliances because it is someone else's "fault" that they are designed that way?

Every danged one of us learned, somwhere along the way, to feel the amount of heat something puts out, often without even making actual contact. I still second guess my electronic meters by feeling a pipe or tank. And, do you know what? I do not spend my evenings in the emergency room awaitng treatment.
Surely, us Neanderthals of society who were able to develop this (what seems to be) great skill of temperature sensing, could SOMEHOW teach these skills to our offspring. Just look at how our generation has taught them to develop their eye/thumb reflexes when it comes to game controllers.

I only touched one radiator once enough to get burned. Now, I'm hooked on radiators and fear that I may actually be addicted to them.

I am Al Corelli and I'm a Radiaholic.

Is this the place I come for the meetings?

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

I said that covering radiators changes the conditions under which it operates. While most covers do reduce output--often considerably--some can actually increase output. But in either case, neither has changed the efficiency of the radiator.

Since water does not exit the radiator at absolute zero (the only way for the radiator to use all of the available energy), the water exiting the radiator is part of the output. Heat emitted from the rad plus heat in the water leaving the rad is exactly equal to the heat input to the rad. Efficiency is always 100%. This is why you can't speak of radiators having "efficiency" in this way.

In a previous message you brought up increased transmission loss due to increased return temp from the emitter(s). Foremost this has nothing to do with the "efficiency" of the radiator! If all of the return piping is in conditioned space, any increased "loss" from the piping just relieves part of the job from the rads. Even if the piping is in an unheated but reasonably weatherized basement, it's hard to even if let alone how much of the heat is genuinely lost by the system.

I can easily think of a four real-world and common situations where removing covers could reduce system efficiency:

1) In a steam system where the effect of the covers (be they original or additions) has been considered with appropriate adjustment made to the sizing of the boiler. Remove covers that have significantly reduced the rad's output and the radition will now be significantly oversized. The rads will be condensing water faster than the boiler can make steam and system efficiency as well as comfort are likely to fall.

2) In a hot water system that began with significantly oversized radiators. Even by Manual J rads size "properly" for the time are likely to be significantly oversized--especially if the system was designed to operate under conditions like windows slightly open or a daily "airing" of the house each morning by opening many windows fully. Both were quite common practices early in the 20th century (and perhaps before). Now say insulation has been added and weatherization improved. The already oversized rads are even more oversized. Uncovered they may rarely--if ever--need a supply temp higher than 125F or so. While a condensing/modulating boiler will love to drive such emitters, a conventional boiler will struggle as it really wants to operate at a higher temperature to be most efficient. The more closely the sizing of the conventional boiler corresponds with the actual heat requirement, the more you have to gain as more of its time will be spent in more efficient operation.

3) A steam system whose radiation is significantly oversized relative to the heat requirement. In this case you're forced to use a boiler that's significantly larger than required by the house as it must be sized to the radiation. With appropriate use of covers, you can effectively reduce the size of the emitters allowing the use of a smaller boiler.

4) A hot water system where some covers are both intentional and were included in the original design. In most cases, the covers will reduce the rad's output thus a larger than "normal" rad was used. This allowed all of the rads to operate evenly near the same supply temperature. Remove the covers and while the temp requirement for those rads will drop, the rest of the rads still need the higher supply temp. In this case it doesn't matter if the system is driven by a conventional boiler or a mod-con--the supply temp requirement remains unchanged. If uncovering the rad(s) results in a relative overheating of the affected space, then you have lost system efficiency by producing room temps higher than required. TRVs will reduce the magnitude of overheating, but they won't reduce the supply temp requirement of the system as a whole since you must still adequately supply the portions of the system requiring the highest temperature!

Ted Robinson

To cover radiators, or not?

As an engineer, I like to look at things in the limit. So why not wrap those hot steam or hot water radiators in a full blanket of insulation? The boiler will cycle on / off quite often and a minimum amount of fuel will be used. But the house will not be heated, right? So (unnecessary) radiator covers will only slow down the heat transfer from the emitters to the room.

John Ketterman

Clearly there's lots of misunderstanding about this.

'Output-reducing' covers are OK to use when there is excess radiation, but the boiler is cast-iron so the water can't be cooler than ~180F. Then the ideal situation is where output is slowed to where the house is still heated in the coldest weather, but just barely (i.e. requires 24-hour heat calls on a design day).

Why? Because slow and steady heat is more comfortable than "bang-bang" heat. But of course, outdoor reset is a better way of slowing down the heating.

Obviously it is not OK to go any further and reduce the output to where the house cannot be heated. (Assuming the radiation is responsible for that in the OP's case, and his boiler is not messed up somehow.)

John Ketterman

As Mike T has already said, heat released in basements and walls is not lost. If spaces are inside the envelope, they are going to get heat somehow, directly or indirectly. If the outside is 0F and the basement or wall cavity is 60F when the house is 70F, that may seem a bit cool, but it isn't 0F.

Now if the pipes are freezing, either there is too much setback or the pipes have been run outside the heat envelope, which should not happen.

The whole business of "don't heat the basement, don't heat the wall cavities" is mostly BS. You can't avoid heating these areas.

[Deleted User]

Congratulations...

You will be rewarded with a higher degree of human comfort, and posssibly lower fuel bills. :-)

What a long strange trip it's been... ;-)

ME

[Deleted User]

Chicken...

poop. Chicken poop generates heat.

But is it for every one? I think not.

It is my experience that if you remove the covers, you can operate at a significantly lower temperature. And being worried about a 180 degree boiler being turned down is rediculous. Been there, done that more times than you can imagine, and have not had any insurmountable problems. Its a matter of pump control.

But smart money goes for the mod con, gets higher comfort and less consumption.

The main reason for radiator covers is for additional shelf space. Why would anyone want to hide a beautiful work of art like a radiator?

NIMH...

ME

Mitch_4

those that

are being burned likely have the temp setting for the rad too high.

Properly done, it should not burn quickly, maybe ...MAYBE if they stay too long

kinda like this..

Mike T., Swampeast MO

Go to a hobby/art store and look for silver mylar faced 1/4" foam board. Mylar is one of the most emissive substances (meaning its an exceptional reflector of radiant energy) and unlike most metals does not oxidize over time thus reducing emissivity. It's easy to work with, quite rigid and has some insulation value to boot.

If you can't find mylar faced foam board, you can always get paper faced and glue on mylar with sprayed or brushed contact cement. (3M "Super 77" spray adhesive is a great product.)

jp_2

missing the point

you've greatly missed the point here.

theres a huge difference between heating unused spaces(wall cavities, etc..)directly and indirectly.

putting heat where its not effective is a waste.

Maine Doug_70

My parents had

a few houses with HW radiators. My mother always wanted them covered with exactly the boxes you write about. They never worked properly after that in every house. These were company houses with mill supplied hot water.
Looked nice though.

gasfolk

Nice Kitty....It Seems That Sometimes Happens...

Hi Al & Mitch,

From the article:

"Eight of the 10 children suffered partial thickness burns that were treated in the outpatient clinic. .... Two children were hospitalized for full-thickness burns. One was a 16-month-old child who touched an exposed steam radiator pipe, resulting in severe burns to the palm of her hand that required a skin graft. The other was a 7-month-old infant who fell out of bed and became wedged between the bed and the radiator, resulting in multiple burns to her left hand, left arm, left ear, and left side of the head that required treatment in a burn unit. Two other children (aged 10 months and 31 months) also were burned when they became trapped between a bed and a steam radiator." That year, 1881 kids nationwide had a lot of sadness--skin grafting is among the more painful experiences.

Our kids are much older, and though they try, they still don't listen or understand. Not advocating radiator covers, government intervention, or any particular action. Just a heads up to parents to consider an unlikely risk.

But this is off topic, and was not meant to irritate or offend.

Thanks,

gf

gasfolk

Hi Mike,

Radiators versus Convectors

The diagram in Dave's link (http://www.heatinghelp.com/newsletter.cfm?Id=77) suggests that radiator enclosures that block radiation and encourage convection increase output, while (for example) the enclosure (second from the left) with an entirely open front (emphasizing radiation over convection) has decreased output.

Is this consistent with current thinking on Mean Radiant Temperature (MRT) and the whole Radiant Comfort movement? I understood the benefit of low-temperature hydronics as the greater proportion of radiant (versus convective) heat?

Thanks,

gf

Mitch_4

Question Mark

I was taught that CI rads should NOT exceed 150. I typically set the boiler H2O to 140 ish (run to ensure condensate is not a prob and 140 is usually good, all NG here)
Never had trouble heating at 140, no burns. Safer too. (see kitty pdf earlier up)

what is your thoughts on CI rad temps?

jp_2

didn't really answer my questions

mike?

i asked for systems that were design properly but would still benefit from covers? your answers were the opposite.

how can a cover,in itself, increase output?

if your radiator law applied to boilers, they too would be 100% efficient.

Mike T., Swampeast MO

Remember that there aren't too many people designing and installing new systems with cast iron radiators--nearly all are existing. I've certainly seen residential systems where covers were an intentional part of the original design. You asked for real world examples where removing covers would not (or were unlikely) to increase system efficiency and I gave four.

According to that old University of Illinois study regarding covers, some cover designs could increase output of a radiator. How? By increasing convection:

"The effect of enclosures without a top was to increase the transmission efficiency of the radiator by about 12% when the area of the inlet [across the bottom & sides] was approximately 10 times the heating surface in square feet."

By keeping the top open but extending the height of the enclosure to 34" above the top of the radiator the increase was approximately 20%. This test was with 38" tall rads, so while output increased, I won't say much for distribution of the warmed air since you've essentially created a chimney inside the room with its top above most peoples heads--I suspect the warm air tended to pool near the ceiling with any increase of output offset by needing more heat to keep the lower area of the room comfortable.

Also note how the author qualifies the word efficiency. "transmission efficiency"

Electric boilers are 100% efficient.

Any fuel burning boiler though has a flue with most of its energy going right outdoors where it can never be used by the system. Radiators don't have flues--they have returns and any energy they haven't liberated is returned right back to the heat source. Yes, I am ignoring differences in transmission loss due to higher supply and/or return temps; not because it's convenient but because piping is often located in heated--or at least semi-heated (e.g. a basement) space. It's NEVER been a good idea to run piping filled with water through an exterior wall but I have seen it done and the dead men insulated the crap out of them and even put them in an insulated duct.

gasfolk

MRT?

So, Mike, if you take into account current concepts of MRT, would you change the relative order of the covers in Dave's Link to favor those with more radiant than convective heating? For example, the model with the open front?

gf

jp_2

so

why is transmission efficiency different from efficiency?
seems to me they mean the same thing.

think you are still playing with words here.

Dave Larsen_11

MOST efficient!

There's an area here no one has touched on yet and I'm curious as to why?! What is the rest of the room doing? obviously this system heated this house prior to the new boiler installation so we have at least the remnants of a working system. I've always told my customers that the best way to lower your fuel bills is to ensure that the heat being put out by these radiators STAYS in the room! Before you remove those covers and possibly have a situation where someone could get hurt, check those windows,r value in the walls,maybe even invest in a little caulk, etc. We may all be arguing about a moot point here. A wise man once said " the most efficient heating system is the one that doesn't run" thank you Mr. Bean

CC.Rob_4

backing up to the OP

I see this is a 92% Burnham boiler. To me, that says it's a hydronic (water) system, and likely a modcon.

Is the reset curve too low?

(Caveat: might have missed something in scanning the posts, but it seems that may have been overlooked).

John Ketterman

No, I didn't miss the point. You don't read my posts or Mike T's; you just continue to say the same things over and overs.

"Don't put heat where it is not needed" is not correct in all cases; just because lots of people say it doesn't mean it is true.

As I have already explained at some length, if heat gets there anyway, it doesn't matter whether you are heating it directly or indirectly. Everything inside the insulation envelope will be heated one way or another.

jp_2

ever hear of

newtons law of cooling?

if so, you might understand my reasons for direct and indirect forms of heating...

its a basic law, the higher the temps the higher the losses, the higher the fuel consumption.

your posts are easy to read, you never show any form of proofs, just " I said so".

NYplumber

Case Study

Is there a case study, or article that shows the reduction in output, particularly radiant output by covering a low temp cast iron recessed radiator?



I have a customer who is bent on having them made, and I would like to convince him out of it, as the heating contractor takes the blame at the end of the day when the heat isn't performing as it should.

Steamhead

It pays to wander off the Wall

go here:



http://www.heatinghelp.com/article-categories/158/Radiators



and scroll down to the Radiator Covers articles.

bob_46

Covers

Manufactures and research people at our universities used to take heating seriously .

bob_46

BIG......PDF

If the pdf above is too big try this and click on pdf file.



https://www.ideals.illinois.edu/handle/2142/4165

icesailor

Radiator Covers:

Doesn't this one cover it?

Doesn't it say that certain designs will increase the output of the radiator through improved convection?'



http://www.heatinghelp.com/files/posts/7867/Radiator%20Enclosures.pdf

icesailor

Covers:

Sorry, it reduces the amount.

NYplumber

Thanks

Icesalor and Bob for the pdfs.

It will support my direction in that the radiators shouldn't be covered.