How many rads will boiler run ?

[mkb]

We're having an extension and will need 3 more rads. Our oldish Ravenheat 820 / 20 runs, at the moment, 6 radiators. Someone said it should run 3 more ok as the boiler is 24 kw ? Rads on the internet say something like 1600 btu or 3000btu so is there a formula to work out, for example, that my Ravenheat could only run rads with a total btu of, say 5000 btu's ?
Cheers

 

[xr4x4]

24kw is 81000 btus.

So u need to work out the rating of the new rads and try and work out the ratings of your old rads, plus a bit for hot water. (2 kw?)

See what figure you come out with..!

 

[kirkgas]

go online and find a radiator sizing chart, try stelrad for starters, then measure your own rads to see if you can work out the output, you need height, length and whether it is single or double panel, with or without fins in between, (look at the stelrad sheet then look down on top of your rad to see what you have) it wont be a perfect match but will be close enough for what you want, simply go round and write down all your rad size/designs then work our what your total output is at the moment, then you need to work out the requirement for the new rooms ( a wee bit trickier but post back on here and the good lads on here will work it out for you if you give us room dimensions) to use a REALLY rough guide multiply the room volume IN FEET multiply by 5 then divide by 3412 to give you kw output, once you have done all this add 2 kw for your hot water, this will get you close enough to see if you are above your 24kw

 

[holty]

why add 2kw when its a combi. OP put it this way i doubt you have 6 rads totaling 4kw each. i use 1.5kw per rad as a rule of thumb.

 

[simond]

Or perhaps I could suggest a quicker way.

Go to www.sedbuk.com, use the Whole House Calculator.

This will tell you the boiler size in kW you need for heating, based on the external dimensions and type of insulation you have at home.

It is pretty accurate, SEDBUK is a UK Government site.

 

[D_Hailsham]

Go to www.sedbuk.com, use the Whole House Calculator.

The Sedbuk calculator can be confusing to use. I would suggest using the Boiler Size Calculator. It will give exactly the same results, just more user-friendly.

However, that will only give the required boiler size, it does not tell you what your existing rads add up to. For that you need the Stelrad Elite Catalogue. Just find the nearest size. Whoever designed the new extension should be able to tell you the heating loss and therefore the required rad sizes.

Just add this to the Sedbuk figure and that's the heating requirement for the house. I doubt if it will add up to anything like 24kW.

The Ravenheat 820/20 is a range-rated boiler for CH, so the output can be set to be the same as that required by the rads - min 10kW, max 24kW. The "out the box" setting is 16kW.

When in HW mode it automatically provides the max, 24kW.

 

[mkb]

cheers all, bit confusing isn't it ?

 

[D_Hailsham]

cheers all, bit confusing isn't it ?

Not really.

1. Use the link I gave to get the boiler size;
2. Use the link I gave to get the rad outputs and add them up;
3. Find out the proposed rad sizes for the new extension;
4. Add 2 and 3 together to get total rad output.

Provided this is less than 24kW, you can use the existing boiler.

Comparing the result from 1 and 4 will tell you if the rads are undersized; it does not matter if they are oversized.

The result from 1 will also tell you if the boiler output needs to be altered from the default 16kW.

Time required - less than an hour (and that's being generous ).

 

[mkb]

Thanks. Will do that.

 

[Agile]

The reality is that your boiler will easily run your rads. Most likely the house next door's heating as well!

Whats more relevant is to correctly size the rads in the conservatory to match the heat loss.

Strictly the conservatory rads should be fitted as a seperate heating zone.

Some think that this requirement is met just by having TRVs. I dont subscribe to that view unless they are the timed type.

Tony

 

[mickyg]

The reality is that your boiler will easily run your rads. Most likely the house next door's heating as well!

what he said.

 

[bengasman]

It's really simple.
One metre of 600 high single panel rad is about 1kW, add the total up and see if that stays below the boiler OUTPUT.

 

[D_Hailsham]

Whats more relevant is to correctly size the rads in the conservatory to match the heat loss.

The OP hasn't said anything about a "conservatory"; it's an extension.

In any case the OP should not be sizing the rads for the extension, thats the job of the person who designed the extension. They will have had to do heat loss calculations to show that the extension meets current Building Regulations.

Strictly the conservatory rads should be fitted as a seperate heating zone.

If any form of permanent (rads, underfloor etc) heating is put in a conservatory, it is no longer exempt from building regulations.