how many radiators for a system?

[AlF2008]

Needing a little more help folks.

I'm trying to figure out how many radiators we can power from our Bermuda Baxi 57/4. I've got the installation manual and it gives plenty of technical info such as btu/h and Kw of output. What factors do I need to take into account when figuring out the number of radiators we can put on the system?

Presumably the length of pipes (currently very poorly lagged) will also have some effect.

Currently there are 6, one of which is about to be replaced with a physically smaller but larger output one. Ideally I'd like to use the radiator we've removed in another room as a temporary measure but need to know whether the system will cope.

Whats the best way of doing this?

Thanks

 

[kevplumb]

aye it will cope

 

[AlF2008]

Thanks for the reply.

I was looking for something a little more scientific. Is there a way to calculate what each radiator takes to heat it?

And if I can do that, can I sum them up and see what the approx drain on the system is in power terms

The power output of the boiler is 14.65kW or 50k btu/h.

 

[kevplumb]

unless they are all 6 ft doubles it will cope

I was looking for something a little more scientific. Is there a way to calculate what each radiator takes to heat it?

yup look in the catalouge for thge rads it will give you the heat output

or dont bother worst case it might take a bit longer to get up to temp

 

[mikej2005]

If you picked up a PTS catalogue like I advised you to do in your recent TRV thread, then there are 10+ pages of radiators from a lot of the main manufacturers with all the relevent stats - find some of a similar size and design to yours and that'll give you a rough idea of the heat output of your radiators.

 

[AlF2008]

yup look in the catalouge for thge rads it will give you the heat output

Trouble is they are old so I doubt the modern equivalent would accurate.

 

[AlF2008]

If you picked up a PTS catalogue like I advised you to do in your recent TRV thread

I did look at the site but to get the main catalogues you need to register and include things like business name (required field). Hence I took it to be for trade only (as the name implies).

 

[wms]

follow this link it will get you started with approx sizes btus etc
http://www.plumbworld.co.uk/600mm-high-central-heating-2001-0000

 

[mikej2005]

I did look at the site but to get the main catalogues you need to register and include things like business name (required field). Hence I took it to be for trade only (as the name implies).

They do sell to the public. I'm not in the trade and replaced my entire central heating system last year, buying most of it from them. Pick up a catalogue instore or find a similar catalogue from any other plumbers merchants.

The only way you're going to get accurate figures is from the original manufacturer's specifications. If you don't have these (as most people with older rads won't) then I'm afraid you're going to have to settle for a rough figure, worked out from the closest matches you can find.

 

[AlF2008]

follow this link it will get you started with approx sizes btus etc
http://www.plumbworld.co.uk/600mm-high-central-heating-2001-0000[/QUOTE]

Thanks. I'll measure all the rads up and have a look.

Do I need to take account of the hot water side of things?

 

[Softus]

Do I need to take account of the hot water side of things?

Yes. As a general rule of thumb allow about 10K Btu (about 3kW) for the cylinder coil, if the boiler is heating the cylinder.

 

[AlF2008]

Great. Thanks for all the replies

 

[AlF2008]

Ok nearly there now

After much looking around I've used the Myson Premier range as my benchmark as they have similar construction to what is currently fitted and also come in 700mm height (existing ones are 750mm) . I've gone for double panels, single convector for the doubles to try and make the comparison fair.

Boiler - 14.65kW

Rads
Bed 1 - 1.6kW
Bed 2 - 1.0kW
Hall - 2.0kW
Dining R - 2.4kW
Bed 3 - 2.8kW (this is a new triple convector, not yet fitted)
Bath - 1.2kW

Total for rads is 11kW.

The radiators we have at the moment dont have convectors so I guess they will give out less heat than this.

Taking 3kW for the hot water which takes it close to the boiler output.
I've also got TRVs to fit onto all the radiators which presumably will help control the heat distribution.

If I was to fit the radiator thats been removed from the system into the sitting room (currently doesn't have a radiator) do you think it would work ok? I'm guessing about the same size as the one currently fitted in the hall.

I presume there is also a reasonable loss from the HW pipes which have what appears to be a cloth lagging. At the moment I must be losing a fair bit of heat under the floor as its damn cold down there! Would fitting modern lagging onto the pipes make a big difference?

Sorry for all the questions but I do really appreciate the advice

 

[JohnD]

Except in very cold weather, or when heating the house from cold after it has been left unheated, radiators do not take as much as the rated value. If you have TRVs they also reduce their load as the rooms warm up.

Probably in the list you were looking at it gives the temperatures of rooms and water for the loads you mention.

In my house the total rating of all the rads exceeds the boiler capacity by about 30%, but it doesn't matter, as they are (almost) never all full on at the same time, since I had cavity wall insulation fitted the house doesn't lose that much heat.

Your bedroom rad is possibly 3 times as big as you will need after it has warmed the room from cold (unless the bedroom ceiling is uninsulated which it should not be).

The cylinder will take a lot of heat if it has just been drained for a bath, but after 20mins or so it will be up to temp.

Climaflex or similar stiff foam pipe insulation will do a lot of good in unheated areas like under the floor or in loft (in heated rooms it just contributes to the room heating, so less important). the BS lagging for unheated areas is as thick as your arm. The economy stuff is cheaper.

And you need to insulate the cylinder well.

 

[AlF2008]

thanks for the reply.

the tech sheet for the radiators states that everything is for a 70 degrees water to 20 degrees air.

Trouble we've got a the moment is that the house is draughty and has no floor coverings and is pretty cold most of the time. I'm working on the draughts but the floor is going to be uncovered in most rooms for quite a while. the house is completely exposed to a north wind like we've been having recently too. The wife doesn't like being cold hence why she chose the biggest 1000mm radiator she could find (and quite possibly on the planet!) and to be honest it wasn't worth arguing. Hopefully the TRV will keep it under control.

We've got approx 8" of loft insulation and there is also cavity wall insulation.

the entire CH pipework is under the floor which ranges from about a foot to approx 3.5-4 feet so there is a lot of cold air under the floor.
what thickness of insulation is recommended fo rheating pipes? most seems to be 13/19mm thick.

I've been looking at this stuff:

pipe insulation

It looks like 13mm is the most popular thickness for the walls. Presumably this would be sufficient for most domestic uses?

Biggest problem is that I cant find anywhere that does the same for 8mm pipes. I could used 10mm but obviously that wont be as good as the correct size. anyone point me in the direction of a supplier of 8mm?

Talking of insulation, does anyone know of any transparent insulation (presumably plastic)? We have a loft hatch which is primarily glass to let light in but obviously lets out a lot of heat.