Appropriate Combi Boiler for 2 bed flat with 1 bath, 1 on-suite, 9 rads, mostly shower use for 2 people

[kiich]

Hi

Been looking at different models of combination boiler to install for a while now - and have narrowed it down to 2 company - Worcester and Vaillant. I know there's others out there but i feel comfortable going for these.

The flat has 3 floors - ground floor which just had an entrance door and a stair leading up to the 1st floor which has lounge and kitchen -

4 rads on this floor.

2nd floor that has 2 bed, 1 main bath and 1 on-suite - 5 rads on this floor.

2 people living in the flat - shower all the time - bath once in a blue moon so not too bothered about how bad combi is at filling bath etc and i have been told about this by this group before.

Ideally I want a medium sized boiler - not a gigantic one like the Worcester 30HE Plus which is 850mm in height - our kitchen is pretty small so space is a preimium to us.

Here are the specific models i've been looking at:

• Worcester 24i Junior height - 710mm width - 400mm dpeth - 330mm

DHW flow rate @ 35C - 9.8 CH Output 7.2-24kW

• Worcester 30Si height - 710mm width - 400mm dpeth - 330mm

DHW flow rate @ 35C - 12.3 CH Output 7.2-24kW

• Worcester 40CDi H - 760mm W - 440mm D - 360mm

DHW flow rate @ 35C - 16.3 CH Output 8.6-30kW

• Vaillant ecoTEC plus combi 831 H - 720 W - 440 D - 335

DHW flow rate @ 35C - 12.7 CH Output 8.7 - 24.0kW Btu/h - 29,700 - 81,800

Also looking at Vaillant ecoTEC pro cmbi as well...

so my question is - are these suited to our flat, number of rads and our needs??

And what exactly do these number means - i know what they roughly mean but i dont have any reference as to what is a GOOD flowrate for this flat and same goes for CH Output - i have been told 35kw for CH Output is good - but i'm guessing the person who told me this is assuming i live in a house and not a flat.

Apologies for being a bit vague - more information can be obtained if necessary.

thanks

[Richard Faulkner]

In message , kiich writes

With hindsight, I would get the one with the biggest flow rate I could afford - I have a Worcester 24i, and find that to get a decent shower pressure, I have to buy heads which have narrow holes. It would be nice to have a bit more flow.

[Doctor Drivel]

Both makes are very good. I would lean towards the Vaillants. Ed here fits them all the time, and he can recommend a model on reliability. I would go for one with a little umph to cope with two simultaneous showers.

If you are DIYing it, then go W-B at:

[Owain]

Domestic hot flow rate at a 35 degC rise between incoming cold and hot (i.e. if the cold water is 10 degC the output will be 45 degC), in litres per minute.

Central heating output, in kiloWatts. Most boilers will modulate over a range, so there is a low and high figure quoted.

Central heating output, in British Thermal Units (obsolete).

Unless you live in a draughty mansion, any boiler should produce ample heat for CH - 24kW is equal to having 2 three-bar electric fires in each of your four main rooms, running simultaneously and continuously.

The area of concern is the shower, 30kW is usually ample for one shower (three times as good as a 10 kW electric shower) but if you are often running two showers at once and like a good shower you might want a bit more oomph.

Owain

[andrewpreece]

I have a Vaillant Turbomax 828 ( 28kW ) and it gives perfectly good showers, and fills a bath in between 10 and 15 minutes depending on season. I am a little nonplussed by all the arguments about bath filling time, since unless you are planning on fittng as many baths as possible into a day, when you desire a bath you simply turn the taps on and come back in 10 minutes to see how it's getting on.

Anyway, what I would suggest is that you figure out what your cold water supply is like, since if you have a poor water supply a high flow-rate combi won't work to full spec. The figure of 20 litres/min at the kitchen cold tap is often mentioned as being a good figure ( mine gives 19 litres/min ).

I note some of the combis you mention are capable of nearly 13litres/min, so you need some slack in hand to cope with this demand.

Andy.

[John Rumm]

Note that the dimensions you quote do not necessarily include the space required for the flue (which normally exits at the top these days). This typically takes 190mm extra. It also does not include the minimum spacing required round the boiler to adjacent cupboards etc. This seems to vary quite a bit with different brands etc, and can be 100mm or more on some, down to as little 5mm on others.

(I had a requirement to fit a boiler into a small space. The only one I found that would fit was one of the Isar range from Ideal at 687, 397,

290 (h, w, d) mm)

That would be my choice out of your shortlist.

As in most cases, you can ignore the heating aspect and focus on the hot water requirement, but check the mains can deliver the flow rate first.

The minimum for a shower that will satisfy most folks is going to be about 8 lpm - so 35kW really is about the minimum if you want to run two at once. You can cheat a bit if you select shower heads carefully - one that gives a more directional blast of water can create the impression of plenty of flow while not using as much as you may think.

35kW for heating is *vast*. If you need more than that you would be better of fixing the insulation!

Being in a flat makes your heating requirement slightly easier - since someone else is paying for the free heat you get coming up from the ground floor ceiling ;-)

[Doctor Drivel]

The Ferroli Domina exits directly from the back.

[Matt]

Fill a bath in 3 - 5 minutes while you peel off your clothes or have a dump and you won't forget the taps are on, leave it a painfully long

10 minutes and the mind wanders to other things, like rearranging the bedroom/chatting on the phone/reading one more thread on uk.d-i-y, next thing you know is the bath is overflowing due to hairs blocking up the overflow and then the kitchen ceiling caves in making a right bloody mess. Then you are up to your neck in Part P for the kitchen and all the hassle that causes.

I know its hard to believe given his record but more houses have been flooded by slow combi filled baths that have been forgotten about than council flats have been by Dribble's hacksaw cut plastic plumbing.

[Doctor Drivel]

[darrenforward]

Dont know if anyones noticed but the prices may not be accurate Quote "*Prices exclude VAT but include Standard Flue, Fixing Jig, and LPG conversion kit where appropriate. Prices correct 20/2/04. All boilers are SEDBUK rated A, and include a 2 year warranty. "

regards

Darren

[Owain]

You have your bath clothed? Is that to stop the nurses laughing at your wee willie winkie? Doesn't the paper nightie dissolve and block the plughole?

[Doctor Drivel]

If you can get one cheaper then lets us know.

[darrenforward]

Has anyone actually purchased anything from

What did you buy and what price was it.

Kind regards

Darren forward

[Doctor Drivel]

You pay what they say on the web site.

[Matt]

No you don't

[DJC]

and the extra insulation from the floors above.

[John Rumm]

Indeed (although I could not tell from the OPs description if there were more floors above their place)

[Doctor Drivel]

Nope. If above is 21C and you are 21C then no heat loss through the floor.

[Dave Plowman (News)]

Well, it was described as a flat with a ground floor, so it's safe to assume there are. ;-)

[Andrew Gabriel]

You might want to read up on floor to ceiling temperature gradients. In rooms heated to nominal 21C in winter with standard radiators, you'll normally find a good 10C temperature difference between adjacent floors and ceilings. In the area directly over the radiator, this can be very much more. It is a significant source of heating for upper floors even when the room temperatures are nominally the same, as anyone who's done whole house calculations will have noticed.

Even with no heating in the summer, you'll find a temperature gradient of around 2C between floor and ceiling of a typical 8' room.