What gas CH and HW system - 200sqm semi 3 baths plus shower?

Hi

I know it has been done to death already, but...

I am extending my 3 bed semi up to 5 beds, 3 bathrooms with showers and a separate shower room, total floor area 200sqm. Obviously the insulation will be up to the latest standards, the roof is being replaced and the existing house has cavity wall insulation and DG.

We have mains gas and at least 35l/min water at the road and we are running a new polypipe from there. I am planning on fitting a water softener, I'm not sure if this has a material impact on flow rates?

Ideally we would like to have all of:
Mains H&C to all taps
Single zone radiator central heating with weather compensation control
Enough hot water volume to have at least one shower and one bath running simultaneously.
Enough hot water heat and volume to be able to top and hot up a bath.

I don't think a combi can meet this level of demand (at least on its own), I have seen suggestions of having a combi for the showers plus a tank for the bath - has anyone done this?

I would rather avoid an unvented tank because of the installation and servicing requirements.

One possibility seems to be a regular vented tank and pump the showers although obviously there are the noise and reliability issues with this approach.

A heat store, possibly with a plate heat exchanger seems another possibility but the system cost is excessive and I am not sure if this approach can be used in conjunction with weather compensation control and there also seem to be suggestions that the higher HW storage temperature is not compatible with the condensing operation of a condensing boiler and is thus less efficient.

Finally - possibly for another thread, decent energy savings seem to be achievable using mechanical ventilation heat recovery. Currently with my kids at home and my wife not working we heat to 21C all day and 18C all night so potentially there are decent savings to be made - does anyone have any experience with these devices?

Thanks for any suggestions.

m1chaels said:

total floor area 200sqm.

Single zone radiator central heating with weather compensation control

Click to expand...

Sorry, but over 150m² Building Regulations stipulate two heating zones. I'm not sure if you can have weather compensation with that.

we heat to 21C all day and 18C all night

Click to expand...

Why 18C at night? Does your house loose a lot of heat overnight? Have you tried setting to a lower night time temperature, say 10C?

Have you worked out what size boiler you require? If not, the Boiler Size Calculator will help.

Which make/model boilers are you considering?

You need to measure the dynamic flow rate at say 1.0 Bar.

35 li/min open pipe will just about fill one bath well.

You dont say how many people live their and their bath/shower usage.

If you read all the existing threads you will be able to get all the answers. You seem to have not done much reading.

Alternatively why not ask your chosen installer for advice? He can see your house and best advise you.

Or employ someone to specify a system for you.

Tony

If it is going to be replumbed, you'd do well to ovesize all pipes apart from those to sink/basin by one step e.g. from streetvalve in 32, to bath in 22 etc.
And get a biiiig cylinder.
Also make sure you get a programmer with independent timing option, so you can program the dhw to be never on at the same time as the dhw.
This gives a huge increase in performance, but for some odd reason most installers still don't use them.

Thanks for the comments so far.

I have decided to go with a standard condensing boiler and retain a vented cylinder and header tank.

I also want to have weather compensation control.

Can anyone suggest a good gas boiler to choose that supports weather compensation (presumably it needs to support two separate circuits running at different temperatures?)- output in the 15-20kw range?

Thanks

Michael