heat exchanger sizing

[oakwoodtv]

I want to connect a combi boiler to to the log burner central heating system
the combi will be used only for hot water in the summer and occasional C H

The combi boiler is rated at 9.2 to 24 k watts
there are three large and three medium radiators on the system
how large a heat exchanger will I require

I have three heat exchangers from worcester 25cdi combis
will this be sufficient       

[therecklessengineer]

Despite just recently sizing a pair of 850kW heat exchangers, I actually have no idea how to tackle this.

Is anyone able to throw some maths at it rather than rules of thumb?

(I do like maths. )

[greasemonkey]

I've been trying to work this sort of thing out as well. So far, I have no idea.............

[knighty]

go on ebay, get a massive one, job done

there's nothing to loose by using one which is too big :-)

[oakwoodtv]

Getting a massive one from the bay is a possibility but I am a tight old git
the three I have now [ measuring 310x75x50 mm 18 plate HE ] cost me the
princely sum of £3.00 from my friendly recycler and if I can series parallel
a few together it will save me cash I do not wont to spend

May try three in parallel and if the boiler cyclicals to much I will
add three more

maths is fine but the suck it and see method works as well