New boiler/central heating after extension

[newbuyer17]

We are extending our 3 bed detached single bathroom hosue to a 5 bed.
Currently we have a non-condensing non-combi ideal classic boiler, with 4 large rads and 3 small rads. Shower is an electric one.

The heating has never been great, and I'd like to upgrade the boiler AND all pipework while we have the chance.

New house will have an on-suite and a bathroom. Ideally I'd like to get something that can heat the whole house, and supply 2 non-electric showers simultaneously. Not neceserily power showers, but something with a bit of oomph. Ground floor is 31m sq, upstairs 41 m sq.

If I put a new supply pipe in (current one hasn't got enough flow for a combi, even though there is enough flow/pressure at the street) what would you recommend?

Is a combi realistic, or unrealistic/unrecommended. I'm also looking at maybe getting some underfloor heating for the new kitchen, which I guess would also run off this.

Apologies, I know this is a very open question, but any initial advice before I start looking further would be appreciated.

Thanks

 

[DP]

Heat only boiler plus unvented cylinder. Solar panels if pocket a little deeper.

OR, combi supplying hw in kitchen and cylinder to bathrooms plus solar to save you gas

 

[Bodd]

As DP said. but make sure you have 3 bar pressure.

If not large CWST and a good in house Pump.

 

[newbuyer17]

Thanks Guys - sorry its been a while. To recap we will have a bathroom with bath and seperate shower, and also an on-suite with shower.
edit - quoted for 12 rads, plus underfloor heating approx 6*3m

The options I've been given are:
1. A vailant 831 condensing combi - will that be enough power/heat/pressure?
or
2. a Vaillant system boiler with unvented hot water cylinder - about another £1400.
or
3. I've also been told about a Potterton Promax HE 'Store' with built in tank, which would be a neater solution but not sure about 150Litres would be enough for 2 showers + bath, or should I be fine? Out of interest, how many litres of hot are needed for a bath?

We'll be replacing mains pipe coming into house, and street pressure is OK.
Any thoughts or ideas?

Thanks

 

[ajrobb]

For two bathrooms you might be a little tight with 150 litres of hot water storage if you want long powerful showers. With a 25 kW boiler, this will take about half an hour to heat from cold. It depends on rate and duration of your showers. Using mains pressure, the two showers are going to be killed while someone draws a bath. If you can accept that limitation, you are effectively designing for two showers to be used together. You need to specify the expected flow rates and durations for the showers. I use 13 litres/min from an ordinary plastic shower head but only a couple of minutes of flow. That equates to about 30 kW in the winter if I used a combi. Larger or multiple heads use more. Realistically, you won't run two showers from a single boiler without some hot water storage.

 

[newbuyer17]

Thanks. Yes, we wont be running a bath at the same time as 2 showers, so thats OK. There is a possibilities of stuff like dishwashers, toilets, washing machines kicking in with cold feeds, which I guess would affect flow/pressure to a combi more than a boiler with a storage tank. Or would it still be an issue with mixer showers?
Not the best at waking up in the morning so will have to allow more than 2 mins in shower. Maybe 10 mins tops? Never really thought about it to be honest.
We did wonder about going down the power shower route. What l per minute are they pulling, or is it going to be totally impractical for either one or both?

 

[bengasman]

First: it all depends on your incoming water mains; you need to tell us pressure plus flow capacity.
Second, it depends on how big a shower you want. 2 "green" showers will easily run of a large combi if your mains allows it, 2 all-body showers will need a huge tank and a huge pump, or a 35 mm upgrade.

 

[newbuyer17]

Sorry, I wont know pressure and flow rates until after the extension is complete and the mains pipe coming into house is replaced.

 

[bengasman]

I seriously doubt a new pipe will make any change to your pressure.

 

[newbuyer17]

Last time it was checked pressure was OK, flow was poor.
Pressure and flow were both OK at the main in the street, as checked by water company.

So I assume we need new pipe to get the flow through into the house. It was 5 years ago though, so can't remember numbers.