Radiator shelves and curtains above radiators...

[Jeremy Nicoll - news posts]

Are radiator shelves a good idea?

Most of the radiators in my house are positioned under windows (with decent quality recent double glazing fitted - more to minimise maintenance because of my long-term illness, than for minimising heat loss though they're certainly better than what was there before).

In most cases the window sills' bullnose front edge projects only by an inch or two over the top of the radiators. I was wondering about fitting radiator shelves (where there's room) or extending the sills forward a bit (perhaps just crudely by temporarily, in winter, fixing a deeper shelf to the flat sill surface).

Some rooms currently have roller blinds (but no curtains); the blinds run within the window recess, only just in front of the window, & thus several inches away from the front of the sills.

If I fit curtains I'm assuming it'd be a bad idea to have them fall past the top of the radiator as that would tend to send heat behind the curtains into the air gap between them and the window. If the curtains are to stop above the sill they either need to be totally within the window recess (which might look a bit odd), or they'd need to hang sufficiently sheer so that they didn't (eg in a fold) project into the room past the front of the sill.

I found comments at:

which say some popularly believed things are myths. For example:

'Radiator shelves save energy by directing heat away from windows and into the centre of the room'

If this statement were true, you would wonder why most radiators are fitted under windows. The reason why radiators are mostly fitted here is to counteract downdraughts. These downdraughts are not draughts from outside - you will have downdraughts even with the most airtight windows. Downdraughts are the result of room air being rapidly cooled on the cold surface of the glass, causing the air to fall and producing a draught. If it were true that radiator shelves direct warm air from radiators to the centre of the room, it would be equally true that shelves direct cold downdraughts to the centre of the room. In fact, neither of these statements is true.

It is also untrue that heat from radiators is immediately lost through windows. This will only occur if the window is open. Radiators are mostly installed under windows because this is generally the preferred position for them.

As ANY radiator manufacturer will confirm, radiator shelves actually REDUCE the heat output from your radiators, typically by around 5%. Therefore, this is hardly a measure to increase your comfort - or to save energy. Avoid radiator shelves.

and:

'Always tuck in curtains behind the radiator when it's dark'

It's sound advice to close curtains at dusk to help reduce heat loss. However, tucking in curtains behind the radiators is not recommended. With most modern radiators, at least half of the heat output is from behind the front panel. If you tuck in curtains behind the radiator, you will restrict the free flow of warm air. In some cases, tucked-in curtains will completely block this passage of warm air, and substantially reduce the heat output. Therefore, the best advice is not to do anything that restricts the free flow of air around the radiators, or you will reduce heat output. This also applies to space under and in front of the radiators, where there should be a minimum of 4 inches clear.

If your curtains drape below the top of the radiator, you must consider buying shorter ones. If you are not prepared to do this, consider tucking the curtains onto the window sill when it gets dark. If the tops of your radiators are very close to the underside of the window sills, ensure your curtains are as short as possible. When drawing curtains at dusk, tuck them onto the window sill. If you're not prepared to do this, it may be better to hang them loose and in front of the radiator, rather than tucking them behind, as this can cause less of a restriction to the free passage of warm air. However, if you have a pelmet above your curtains, then leaving them loose and in front of the radiator is not advised. You'll need to use a bit of judgement. Allow plenty of space for air to circulate freely around radiators.

This suggests to me that curtains dropping above the sill should ideally actually touch it, sealing off the curtain-window air gap, rather than come to a stop - say - 1/2" above the sill.

I don't have a wife or girlfriend to impose too much 'cosmetic necessity' on whatever I do, but I don't really want the windows to be too ugly.

Comments welcome...

[Roger Chapman]

Depends on compared with what ...

What radiator shelves do is deflect the rising air behind the radiator away from the wall. With or without the shelves that air is going to mix with the cooler air coming out of the bottom of the window recess but if it stops the heat going behind a curtain then that surely is a good thing.

The usual reason given for positioning radiators in front of window is that windows are usually the coldest part of the walls and radiators positioned there reduce the temperature gradient across the room more than positioning them elsewhere. From that point of view the worst place to position them is on an inside wall.

We need to ask what happens to that 5% of heat that is supposedly lost. It seems to me that the wall behind the radiator will benefit only marginally and that that 5% heat loss is more a case of heat less so the radiator gives out less heat because the air flow from behind the radiator is restricted.

With modern single panel radiators with fins more than half the heat output is on the wrong side of the radiator but tucking the curtain behind the radiator will nowhere near cut off the rising air completely. The great majority of the heating surface is on the fins in an area not actually obstructed by the curtain.

Hanging the curtains over the radiator seems bizarre. That would channel the larger part of the radiator output up the wrong side of the curtain and will encourage the development of a rotating air system within the window recess regardless of any pelmet. You want to direct as much heat as you can into the room, not the window recess.

I would go along with that. Keep the cold air behind the curtains as much as possible. Leaving a gap at the bottom is an open invitation for the cool air to leave the window recess to be replaced by warm air going in at the top of the recess.

You could always cut a close fitting block of insulation and stuff that into the window recess at night. That would really cut down the heat lost through the windows.

See above ...

[Mike Clarke]

An extravagant solution. Just shorten them instead!

[Gazz]

i often wonder why the continental method isnt copied over here, insulated external roller shutters on the windows,

ok they are not as easy as hanging a pair of curtians to install, new builds usually have the roller part in the wall, but retro fit ones have the roller external, which some may not like (i couldent care less, i live in the house so sod what people think looking at the outside of it)

operation can be manual, i.e. you pull on a flat ribbon jobbie by the side of the window (on the inside obviousely) and roll the shutter down, or can be electric, from a button by each window to a timer/remote controlled whole house system, handy to make it look like someones home when they are away on holiday, tho the shutters down are a pretty good security feature.

Most of the ones i've seen have slits in the individual slats, so you can let light in by raising the shutter slightly to expose the slits at the top of each slat, so no need to wind them all the way up just to let a little light in on a morning, and when the shutters are fully down it's black out conditions, great if you have a south east facing bedroom like i have, and a bloody street lamp across the road from the house.

[Roger Chapman]

Never seen anything like that for sale in this country.

[grimly4]

I've seen them for sale thirty years ago. Never saw any installed, though; it was a very expensive system and I suspect the brochure pics were German.

[Andy Webber]

I once had a flat which had a large Critle window, and a large double panel radiator (without fins) on an inside wall opposite. The curtains were long enough to hang past the sill but not to reach the floor. I can attest that this resulted in a significant cold draft at floor level from a large convection flow, which was quite unpleasant. Double glazing and curtains that reached the floor solved that problem.

I believe that there is a theory about radiators under the window that results in a small loop of cold air in a triangle between the window, sill and ceiling that helps push the main warm air circulation into the room. I'm not saying I'm totally convinced by the theory, just that it is a theory I've heard. And of course, as above, having the radiator opposite is awful. But curtains (or blinds), done well, will be effective at keeping the cold air trapped against the window and the warm air in the room.

Cheers Andy

[<me9]

Big problem if the window is a patio door, as in our dining room. We have a tall double panel next to it instead.

The biggest problem is SWMBO has her computer (which she is glued to) at the opposite side of the door, and thus sits in the cold spot.

I'm contemplating (veeerrryyy sssslllloooowwwlllllyyy), UFH.

[Roger Chapman]

The problem with UFH is that as a retro-fit it is very expensive to implement and because of the time it takes to warm up much better suited to old fogies like me who spend much of their time indoors over winter unlike most younger folk who spend their weekdays away at work and their evenings and weekends out spending money rather faster than they earn it.

[The Natural Philosopher]

It also works well in countries where its SO bloody cold that its dangerous to small children and plumbing to not run heating 24x7.

Ultimately if I built another house I wouldn't use anything else.

And Id probably heat pump it as well.

But the retrospective installation cost is MASSIVE

[Alan Braggins]

Yes. I liked ours until the pipes perished, but the work involved in replacing it was just too much, so I've got radiators upstairs now. Downstairs would be even more work, so that'll be radiators when it fails too. Unless I win the lottery in the meantime, which is unlikely, especially as I don't buy tickets....

My mother's new build bungalow is UFH with air-source heat pump.

[Roger Chapman]

On 06/12/2011 13:00, Alan Braggins wrote:

I have been toying with the idea for the last couple of years but the cost is, as you say, massive and the disruption is not to be sneered at either. One of the previous owners of this house ripped out the stone flag floor and replaced it with concrete on a very flimsy polythene sheet with the result that there are some damp patches. I really must do something but the ifs and buts get in the way. Ideally such a scheme would include UFH, shifting the open staircase out of the living room and various other linked jobs. I am waiting for a hernia operation at the moment but in principle I still have enough strength to break up the concrete and dig out another 6" (or whatever) of solid clay interspersed with large stones. I reckon that shouldn't take me more than about a month working 6 hours a day, seven days a week and should save a considerable sum but then there is whether I should actually go for UFH or not (less excavation), combine it with a ground source heat pump, and if I go for that whether to dig up most of the garden or put the ground loop out in the nearest field. Then there is the staircase whose intrusion into the living room has been a major source of annoyance ever since I moved in. The easiest solution might be to build an extension just for the stairs but I doubt whether the planners would let me as this is green belt. I can squeeze it mostly into what is presently a cupboard downstairs but lose a chunk of bedroom upstairs. Decisions, decisions, ... in the end I will probably do nothing since the best years of my life have long since passed and I still have several unfinished projects about the house already.

My nearest neighbours recently had a bungalow built in their garden. That has a ground source heat pump which seems to suit them well.

[Dave Liquorice]

UFH because it has such a long warm up (think days) just needs a change of mind set. From it's cool turn the heating on, it's hot turn the heating off, to set the temperature to cool comfortable and leave it switched on 24/7, let the thermostat(s) deal with controlling it. If required have some more "conventional" rapid response heating but that shouldn't be required in normal use.

[Roger Chapman]

Theoretically at least any heat used when not needed is wasted. You can't escape the wasted heat as the house cools down but maintaining too high a temperature during regular periods of absence of lack of need does cost.

The occasional (or otherwise) need for rapid response heating is also an issue if that has to be expensive electric rather than relatively cheap gas. I have my early and late temperature set to 19C and daytime to 17C but I have been spending more time of late sitting in front of my computer and find that the cold becomes noticeable before it drops to

17C and I have to reach up and tweak the temperature. Same thing happens in the afternoon as that is another time zone. With underfloor heating I would not be able to do that but on the occasions I find time to do any housework 19C is definitely too hot for comfort so a constant 19C would also be a bind.

I don't think a concrete slab takes days to warm up (old houses with

2foot walls do) and depending on whether the insulation is placed on or under the main slab makes a considerable difference to the time lag. (Decisions, decisions ...)