Replacing old radiators - aluminium??

Eskarina Smith

Howdy, does anyone know if it's advisable to replace just a few 30+ yr old steel radiators with aluminium ones, leaving the remaining steel rads in use?

We have oil central heating, rads are all working fine but looking worse for wear. We like the look of the Comfort aluminium rads from Heatmerchants but we heard (though not from a plumber - there's one calling in at the end of the week) that they might get very hot compared to the steel ones, if we are not replacing all our rads.

We have 14 rads of various sizes, we'd be replacing 3 big ones and one small one.

The initial plan was to put in radiator covers to hide the tatty ones but replacing them is the preferred option now.

Grateful for any thoughts.

10-10-20

Hi, you've been given some misinformation there by the look of it. Rads give out heat based upon the temperature of the water in the heating circuit. A correctly sized alu-rad should be no hotter than a similarly sized steel one, unless there has been a change made in the heating system. Alu rads do tend to be more efficient due to their lower water volume (you're heating less water overall to heat up the house) but that effect isn't noticeable outside of the operation of the boiler as it still needs to bring the whole system up to the temperature set on the dial.

So if you did feel that the alu rads were hotter than the rest of the rads (and it was a scald/burn concern) then you would simply turn the boiler temperature down by a notch and reassess the heating again later. As for rad covers - they aren't recommended as they trap the heat and cause inefficiency within the system.

So yes, by all means you can replace some with aluminium and leave the remainder of the steel ones on the circuit - as long as the new rads are correctly sized.

Sleeper12

Covering rads reduces the heat output. They aren't a great idea. Could add 10 to 20% to your fuel bill.

drury..

https://www.boards.ie/discussion/comment/122388952#Comment_122388952

Would it ?

I would have assumed the efficiency of the system would remain the same

Sleeper12

https://www.boards.ie/discussion/comment/122388975#Comment_122388975

The covers are designed to let as much heat out as possible but not all the heat gets out. It's like drying clothes on the rad. It costs more to heat the room

Rule of thumb is always cover a hot water cylinder and never cover a rad.

drury..

https://www.boards.ie/discussion/comment/122388993#Comment_122388993

Im still not convinced but open to correction

I can see the room doesn't heat up as much but i'm not seeing the heat loss

Sleeper12

https://www.boards.ie/discussion/comment/122389017#Comment_122389017

If the room doesn't heat up as much then it costs more to heat the room.

Trust me on it. I am a plumber 👍

drury..

https://www.boards.ie/discussion/comment/122389028#Comment_122389028

I'd await a second opinion on that

Sure i'm a spark but I know from experience it means f all

Sleeper12

https://www.boards.ie/discussion/comment/122389034#Comment_122389034

As a sparks I assume you have done calculations on cable size required for things like an electric shower. If it's 8.5kw shower you'd be happy with 6mm on a 15 meter run. You most likely wouldn't put 6mm cable on the same run if it was going to be totally covered in insulation and running through the hot press because you know that covering something keeps the heat in.

Likewise a plumber calculating the BTU RAD requirement increases if it is going to be covered. Covering most things keeps heat in

10-10-20

https://www.boards.ie/discussion/comment/122389034#Comment_122389034

It's easy - you don't get the full heat-transfer off the rad if it's covered as the ambient temperature increases around the rad. So think of two rooms - one at 10C and the other at 30C, both containing the same sized rad. The room at 10C can draw out more heat from the rad (rate of heatloss off the rad) and the delta-T (difference between the incoming and outgoing water) can be quite large. In the 30C room the delta-T is always going to be less as the rate of heatloss off the rad is less (by 20C in fact).

The same applies with a cylinder. For a given output of a boiler, you can input more heat into a cold tank than you can into a warm/hot tank of water as the heat exchange principals of conduction and convection work better where there is a larger difference in delta-T.

Lenar3556

https://www.boards.ie/discussion/comment/122388993#Comment_122388993

Not necessarily, It depends on the particular circumstances.

Covering a radiator in any manner will reduce the heat output to the room by some degree, but that will actually reduce energy consumption per hour that the heating is switched on, as there is reduced heat transfer to the room and therefore reduced demand on the boiler. Much the same as fitting a slightly smaller radiator in the first instance.

A running cost increase could arise in circumstances where temperature controls are fitted within the room with the covered radiator, and there was significantly increased boiler runtime to satisfy the rooms set temperature (potentially overheating other rooms on the same circuit too).

I wouldn’t see radiator covers as a particularly bad idea. This is a 30 year old installation, often radiators won’t have been very accurately sized and balanced in the first instance, so I wouldn’t be getting too hung up on the impact of covers, unless the house is particularly slow to heat up in the first place.

Whatever the planned works, consider adding at least one room thermostat to the system and have an experienced heating guy accurately balance the radiators to meet the heat requirements in each room. The payback on this usually makes it well worthwhile.

Sleeper12

https://www.boards.ie/discussion/comment/122389196#Comment_122389196

Maybe I'm reading this wrong but if you are saying that rad covers don't let out as much heat then the outcome is cooler room or takes longer to get up to temperature.

My point is to have & keep the room at 21 degrees costs more with the rad cover than without the cover.

10-10-20

https://www.boards.ie/discussion/comment/122389250#Comment_122389250

Oh yeah, and more significant losses with condensing boilers too as they'll be less likely to get into condensing mode due to the poor delta-T.

Lenar3556

https://www.boards.ie/discussion/comment/122389250#Comment_122389250

Not necessarily. There is no real impact on the efficiency of the radiator. By the same logic if you replaced the radiator in your sitting room with one twice the size of the current one, it will heat the room faster but won’t bring about an energy saving.

Lenar3556

https://www.boards.ie/discussion/comment/122389327#Comment_122389327

If the system is correctly balanced you can achieve the same differential temp on a condensing boiler with radiator covers as without.

10-10-20

https://www.boards.ie/discussion/comment/122390592#Comment_122390592

I hate to disagree but how do convection and radiation work as well in a confined space as they would in an open room? Even pushing a couch up against a rad will have a negative effect in terms of heat transfer. I can't equate what you're saying to what we all know around thermodynamics.

Wearb

https://www.boards.ie/discussion/comment/122390898#Comment_122390898

The cover will reduce the speed of heat transfer but have very little effect on boiler efficiency. As said above, it's akin to having a smaller radiator.

If the radiator has been closely sized eg for a temperature of -5⁰ and you cover it, it might struggle to heat the room when the temperature is -5 and below. This can be temporarily offset by turning the boiler temperature up.

Ideally, the customer should be asked (at time of designing) if they intend to have covered rads.

Aluminium radiators give off heat more quickly, but that doesn't make them cheaper to run, unless one wants to get very pedantic about it.

Also those covers are designed to not interfere too much with convection.

coylemj

Surely covering the radiator means it's going to take longer to heat up the room initially but overall, all of the heat energy is eventually going to go into the air in the room?

The heat has to go somewhere. The cover can soak up some of it when the boiler fires up but after a while, all of the heat will enter the room. And when you switch off the boiler, some residual heat contained in the cover (and the rad) will be slowly released into the room. If you say this will be insignificant, so will the amount of heat the cover soaks up in the first instance, when you switch on the heating.

Sleeper12

https://www.boards.ie/discussion/comment/122392818#Comment_122392818

There are several issues with this train of thought. TRVs can't function if covered. The convection rad is designed so that the heat hits the ceiling and bounces to the ground a distance from the rad. So covering the rad doesn't allow the convection process to function correctly. These rads are literally designed not to have anything above them.

Even ignoring all the above and going ahead with the rad covers it can't be as efficient. The rooms will take longer to heat up. Most people will increase the settings on the TRVS or boiler to compensate for slower heating rooms. Increasing these increases the running cost of the heating.

The heat is stored in the cover & yes will eventually go back into the room but that's not much good if you are going to bed or leaving the house and this stored heat is released when you don't need it. As already mentioned above the boiler may not go into condensing mode as ofter so boiler efficiency drops.

Every rad in my home has a smart TRV. I couldn't control my heating with rad covers.

If you contact the technical department for any rad manufacturers they will tell you their rads aren't designed to be covered.

My own mother drys clothes on rads. Like a lagging jacket on a hot water cylinder this lags the rad & doesn't let all the heat into the room. The temperature of the water in the rad has to be set higher to put out the same amount of heat compared to the same rad without lagging

Sleeper12

A quick Google search will bring up many links & they all seem to agree that rad covers do reduce the efficiency of the heating system

Wooden radiator covers, which are the most common, are the least energy efficient with a study by Liverpool John Moores University revealing that they can reduce heat output by up to 40%,’ Rhiannon reveals

https://www.idealhome.co.uk/house-manual/home-energy/do-radiator-covers-block-heat

Lenar3556

https://www.boards.ie/discussion/comment/122390898#Comment_122390898

There is no doubt covers will affect convection and radiation leading to an overall reduction in heat output per m2/h. By how much depends on the type of cover, but it could potentially be significant.

But that doesn’t mean that you will use more energy to heat your house. Indeed if you were to look at a typical house built in 2004, unzoned, and without temperature controls. Fitting radiator covers will reduce the oil/gas consumption per hour that the heating is switched on, together with the heat output to rooms. The two will be roughly proportional.

Wearb

https://www.boards.ie/discussion/comment/122393564#Comment_122393564

Yes. Less energy per hour consumed by the boiler, but more time needed to bring the house up to a given temperature. The overall cost to bring the house to that given temperature will be roughly the same, with or without rad covers.

It just takes longer (with less hourly fuel consumption) When using covers.

Lenar3556

https://www.boards.ie/discussion/comment/122392945#Comment_122392945

The operation of TRV’s would be an issue alright. My own view would be that tying to take a room temperature right beside a radiator is problematic and the value of TRV’s is rather limited in the first instance and a poor substitute for a room thermostat.
The digital smart ones may have software to overcome some of these limitations.

Other than that it is largely a case of radiator sizing. A covered radiator is effectively smaller than an uncovered one. The practical impact of that will vary between dwellings and particular setups. However it is as likely to lead to a reduction in energy use as an increase.

Lenar3556

Not the most informative article. Although the consensus of the author is that radiator covers don’t present that much of an issue.

And in the majority of applications I would agree.

Sleeper12

It was a limited article alright. I was just showing that almost every link saying that rad covers (particularly wooden ones) reduced the efficiency of the system. In fact the only sites claiming no efficiency loss are sites selling rad covers.

Saying that in most cases rad covers don't present much of a problem is saying that they do have a least some impact in most cases.

The vast majority of homes have TRVs. People got them even if they didn't want them because they up the BER rating. You could get a rad cover that doesn't cover the TRV or tail but apart from looking out of place, you would push the cover tighter to rad & reduce airflow.

Personally I've never minded the look of rads. I rarely even notice them in people's homes at this stage. Even the old ones can be spruced up with the right paint.

It's a debate I don't think we'll get to finish. It's difference of opinion. I've looked & I can't find the smoking gun 😊

youtheman

Adding a radiator cover will reduce it's ability to transfer heat. It's simple physics. The amount of heat a radiator transfers depends on a) the effective area of the radiator, b) the temperature difference between the radiator and the surrounding air and c) the heat transfer coefficient. You can buy radiators with a fan and this increases the heat transfer co-efficient. Think of it this way, you want the radiator to heat the air directly in contact with the radiator, then you want this warm air to move, be replaced by colder air, and then repeat the process. If you add a cover then you and impeding this process (the natural air flow over the radiator). As somebody else said here you want to lag your hot water cylinder to reduce the heat transfer, but you want to do the opposite to your radiators, you want to let them lose loose as much heat as possible.

Lenar3556

https://www.boards.ie/discussion/comment/122394445#Comment_122394445

Agreed, and I don’t think there is any dispute around this. Yet, a homeowner may wish to fit radiator covers for reasons of aesthetics, and the question arises as to what is the material impact, of doing so.

The answer is it will vary depending on the individual circumstances, particularly the sizing of the radiator relative to the heat loss from the room at a given time, and the type of room temperature controls in place (if any).

But at a basic level, a radiator which is transferring less heat to a room (because of the cover) will be drawing proportionately less energy from the central heating circuit. Fitting a cover doesn’t impact on the energy efficiency of the radiator. It simply reduces it’s output a little, with a roughly corresponding reduction in oil/gas costs.

So what’s the problem? In a lot of cases there isn’t one. Care may need to be taken around the operation of TRV’s if fitted and potentially room thermostats. Similarly if a radiator is already undersized, then fitting covers will worsen the situation. In this regard homeowners should seek advice before fitting covers if the above arrises in their case.

dathi

if the rad cover is blocking heat transfer to the room it will transfer the heat to the wall behind the rad, raising its temp, which will result in extra heat loss through the wall, that's if the rad is on an external wall

Sleeper12

https://www.boards.ie/discussion/comment/122399096#Comment_122399096

Correct. This is why they recommend placing foil to the wall behind the rad to reflect some of the heat back in.

10-10-20

https://www.boards.ie/discussion/comment/122399141#Comment_122399141

But the foil will only reflect some of the IR energy, effectively a small proportion of the rad's output, so won't contribute significantly to prevent loss through an external wall at all.

youtheman

https://www.boards.ie/discussion/comment/122399096#Comment_122399096

A radiator transfers most of the heat by 'convection'. So you may transfer some of the heat to the wall, but it still won't make up for the loss of the overall heat transfer.

Can't understand why the manufacturers of these radiator covers don't puts some small electrical fans in the housing to help the air flow through the system. Now there's a idea for 'Dragon's Den'!.

Sleeper12

https://www.boards.ie/discussion/comment/122399267#Comment_122399267

I agree. Also how many people remove a rad to allow access for the foil when fitting rad covers