Heating / HW design - Long post




My house currently has an electric immersion heater and electric heating. I'm looking at central heating, and trying to see if I can cut prices by doing as much of the work as possible myself, then getting in a pro for the rest. I have a gravity fed hot and a poor mains flow rate (8l/min) so a combi isn't really an option. Plus, I would like solar hot water next year when I have the money.

My inital plan is...

A Vaillant ecotec plus 18 system boiler, running in 22mm copper to the airing cupboard, through a motorised Y-plan diverter valve, splitting between a vented, dual coil cylinder and central heating. Central heating pipe will be 22mm barrier plastic for feed and return, and 15mm chromed copper for all exposed pipework.

I was looking at a Worcester greenstar i because they also have the option of an integrated diverter valve. Unfortunately, I believe it only comes in 12/24Kw, not really the right size for my house. Since I'll be installing an external diverter, are my ideas about the boiler controls (below) correct?

I was thinking of the vaillant 7-day programmer with weather compensation and room stat. Does this mean I need to install the programmer in an appropriate area, then run one wire from it to the boiler and another to the airing cupboard (for cylinder stat and diverter control), and it will do the rest.

I've calculated total central heating demand as 30,000 BTUs. Would you agree an 18KW is appropriate, or would a 12/15 be more efficient since the heating and HW will rarely both be running at full pelt for long.

Planning my drops I would like to run three rads (total to 11,000 BTUs) from one 15mm drop. Would this be OK, or would I need to run the drop in 22mm?

As most system boilers have internal bypasses, would you still recommend leaving one rad without a TRV? I was considering doing this with the bathroom towel rail. Also, must the room with the stat/programmer have a rad without a TRV or can it do so anyway (I can see this being counterproductive).

Once I've got a good idea, I'll need to find a plumber/heating engineer near me (Gloucester) who's willing to commission (and possibly supply) the boiler, including all the gas work. Any idea how hard it will be to find someone whos willing to do this?

Thanks for your help

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26 Jun 2004
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United Kingdom
I would ask you why you want to use plastic pipe if you are going to do the work yourself.

The cost of copper is about the same and almost all professionals would prefer copper.



Firstly I'd worked out that plastic would have been about 50 quid cheaper, not a lot I know.

Second, pushfit is easier and quicker than Yorkshire fittings

Third, I find it easier to get a coil of plastic and unroll it through drilled joists, rather than having to use the bending spring and Yorkshire couplers every 2m length of tube and notching joists.

I could do either, I've read all the arguments on here about both and might go all copper.

Do you have any advice on the rest of the system?
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