Radiators go cold very quickly - why?

[JoeJoe]

I have a brand new combi running 18 radiators + 1 shower in my house. No complaints there.

Problem is that the radiators seem to be getting very cold very quickly as soon as the boiler is switched off. My suspicion is that the cause could be because some of the pipes (copper) hat feed the downstairs radiators are not insulated. I have a 1m high space under the house, where the pipes are located, and it is freezing cold and drafty there.

Does it make sense? Will it be a good idea to insulate the pipes? It shouldn't be a very big job.

What shall I use? I was thinking about something like this (

, but: 1. it seem to come in various levels of thinkness (which is suitable?), and 2. it may be tricky to fit in some places.

Any advice will be much appreciated.

[Grunff]

Not really. Once the boiler shuts off, there is no more heat input into the system. The various components will lose heat to the surroundings. The rate of this heat loss will depend on how good each component is at losing heat. Radiators are, by design, good at losing heat.

Certainly not a bad idea to insulate them, but it won't make a measurable difference to how quickly your radiators lose heat.

The thickest you can fit in.

If you can't reach a particular piece of pipe, just leave it.

[Dave Baker]

Good. It means they are doing their job, i.e. radiating, very well.

My suspicion is that the cause could be

No. 99% of the heat loss from the radiators will be to the room itself. Only a tiny part will go back down the thin pipes to radiate under the floor.

Will it be a good idea to insulate the pipes?

Of course. You're losing heat to the underfloor space all the time the pipes are hot while the boiler is on.

-- Dave Baker Puma Race Engines

Camp USA engineer minces about for high performance specialist (4,4,7)

[Dave Plowman (News)]

If the boiler is off there's no point in the pump running so the temperature of pipes elsewhere shouldn't make any difference.

[Dave Fawthrop]

|I have a brand new combi running 18 radiators + 1 shower in my house. No |complaints there. | |Problem is that the radiators seem to be getting very cold very quickly as |soon as the boiler is switched off. My suspicion is that the cause could be |because some of the pipes (copper) hat feed the downstairs radiators are not |insulated. I have a 1m high space under the house, where the pipes are |located, and it is freezing cold and drafty there. | |Does it make sense? Will it be a good idea to insulate the pipes? It |shouldn't be a very big job. | |What shall I use? I was thinking about something like this ( |

, but: 1. it |seem to come in various levels of thinkness (which is suitable?), and 2. it |may be tricky to fit in some places. | |Any advice will be much appreciated.

Definitely insulate under floor pipes *ASAP*. I am in process of doing some myself. I am using the Water Regulations stuff from Wicks, IMO well worth it because of the thickness of the insulation. It is very stiff and difficult to get on the pipe. I open the insulation up till the other side almost splits, shove it on the pipe, and hold it on place with Cable Ties. Where necessary I trim a bit of insulation away, with my specially sharpened Swiss Army Knife.

The only problem I have had is that my Swiss Army Knife is used as a fob for the Car keys, and I left it under the floor, and did not want to go there to retrieve it in half way clean clothes. :-(

[Dave Fawthrop]

|JoeJoe wrote: |> I have a brand new combi running 18 radiators + 1 shower in my house. No |> complaints there. |> |> Problem is that the radiators seem to be getting very cold very quickly as |> soon as the boiler is switched off. My suspicion is that the cause could be |> because some of the pipes (copper) hat feed the downstairs radiators are not |> insulated. I have a 1m high space under the house, where the pipes are |> located, and it is freezing cold and drafty there. |> |> Does it make sense? | |Not really. Once the boiler shuts off, there is no more heat input into |the system. The various components will lose heat to the surroundings. |The rate of this heat loss will depend on how good each component is at |losing heat. Radiators are, by design, good at losing heat. | | |> Will it be a good idea to insulate the pipes? It |> shouldn't be a very big job. | |Certainly not a bad idea to insulate them, but it won't make a |measurable difference to how quickly your radiators lose heat.

But will make a huge difference to your Gas bill.

[PeTe33]

With 18 radiators I think the ££ difference would be pretty insignificant.

[Guy King]

The message from "JoeJoe" contains these words:

As others have said, it'll only really matter if the pump is still running once the boiler's off. I'd lag the pipes in the cold space anyway, but radiators do cool down quickly - that's what they're for!

[Grunff]

I doubt it, a few percent at best. No doubt it's worth doing, but don't expect huge savings.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "JoeJoe" saying something like:

The underhouse pipes are obviously losing heat - and if the pump is continuing to run after the boiler shuts down, then the colder water from the pipes is entering the radiators and cooling them down. Even if the pump isn't running, the next time it starts, it's shoving cold water into the rads before the hot stuff (which has lost some heat to the underfloor) arrives.

So yes; insulate, insulate, insulate.

[Dave Fawthrop]

|Dave Fawthrop wrote: | |> But will make a huge difference to your Gas bill. | |I doubt it, a few percent at best. No doubt it's worth doing, but don't |expect huge savings.

Well in my case the pipes have about half the surface area of the radiators, at double the differential temperature.

Work it out for yourself, I am busy with the job.

[JoeJoe]

Thank you all for the very useful advice. Although I am sure that the pump does not continue to run once the boiler is turned off, it still makes sense to insulate the pipes anyway.

Looks like my Saturday is booked then... ;-(

[Dave Liquorice]

Unless the boiler needs pump overrun which modern low capacity ali ones generally do. B-)

Well I suspect that exceeive cooling of the pipes could well set up gravity flow through the rads, though that would depend a bit on the layout. Certainly worth insulating the pipes in the void but prehaps leave a short section un insulated to provide a little background warmth down there.

[Clint Sharp]

In message , "Dave Plowman (News)" writes

Does nobody over run the pump anymore?

[Dave Plowman (News)]

Until the rads go cold?

[charlieB]

Just a thought - check that all your radiators are properly bled of air

- a part full rad looses heat faster when the boiler is switched off

Charlie

[Clint Sharp]

In message , "Dave Plowman (News)" writes

That wasn't quite the point I was making, just that "If the boiler is off there's no point in the pump running" is not entirely accurate, pump overrun can help the system extract heat from the boiler that would otherwise be wasted. Something in the back of my mind tells me it's kinder to boilers as well but that may not be true.