new install / boiler quickie (it started as a quickie anyway...)

Condensing every time....

(Take 400 divided by 15% of your annual (boiler related) gas bill... if it comes to less than say 15 (reasonable life expectancy of a combi) then you are winning - and that assumes that gas prices never go up!)

Having just done the calcs for my place, I came to the conclusion* that the choice of boiler is going to be governed by the desired hot water flow rate and not much else. Since one that can give a decent flow is likely to be well over specced for CH purposes. The more difficult issue may be finding one that can modulate *low* enough for the heating requirement to prevent excessive cycling.

• calcs for my place came out at about 8.5kW - 3 bed semi, double glazed, 4-6" loft insulation, 9" solid walls. This includes the requirements for the loft conversion I am about to do. So yours ought to be better since you have one less outside wall and cavity walls.

(I can post up the spreadsheet for the calcs if you are interested)

Thanks, but I wouldn`t have a clue what the hell I was looking at :-}

It's not that complicated - just a way of working out how much energy you need to stick into a house to cope with all that which will escape through the walls, windows, floor etc. Try here from some background:-

Most of the house i`m sure would be easy to work out - what might be more difficult is the sodding great big dog flap (the largest you can buy) immediately adjacent to the only bathroom in the house - on the ground floor - in the flat-roofed extension.

It seems to be permanently open, either with the dogs having a look out to see what`s happening, or the wind blowing it open, so i`m guessing the air changes per hour calc would be off the scale :-(

The extension connects to the kitchen, which runs the full width of the house, but there`s nowhere a rad could be fitted in there, so its probably a case of oversizing the bathroom as far as possible given the space available to make up for it :-}

This also assumes you have no higher repair bills with the condensing boiler.

True, although nowadays if you buy a reasonable quality one, there is no reason to suggest that you would.

The main incremental parts are the condensate collection pieces. Stainless steel heat exchangers and down or radial firing burners are used. Obviously stainless steel is more expensive than some of the other technologies, but allows a more corrosion resistant heat exchanger.

Microprocessor based controllers and electronics are used, but then they are also used on the better conventional boilers as well.

.andy

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The odds are we`d go for a Worcester Bosch, and from lurking around here for a while they seem to have a fairly good reputation

Doing the calcs on a spreadsheet make it easy to play with what-if variations like that, e.g. stick in 3 (or 10!) air changes per hour and see what that'd make the heat loss. Then you can have some idea how much you might want to oversize the rad for that area to cover the extra losses.

Google 'author:mcardle', 'kickspace' and 'kitchen' :-)

I know, but i`m not sure how durable one of these would be given the amount of fur the two dogs shed :-} (i`d already thought about it)

Why should a condensing boiler have higher repair bills? Answer: they do not.

Err.... I didn't say that....

.andy

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I didn't say you did.

I know. You snipped the headers in the wrong place, that was all.

.andy

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The more complex you make something, the more likely (and costly) it will be to need repair.

I'm not saying you can't make a condension boiler which is extremely reliable, but when taking overall running costs into the equation it should be considered. Which prats like IMM, who only read adverts, fail to realise.

Got the quote back...

=A32100 for a Worcester Bosch 28Si2 =A32700 for a Worcester Bosch 30HE

Not sure I can justify an extra =A3600 bearing in mind the level of=20 savings, 0.5 lpm hike in DHW flow, and the potential lifespan of the=20 install / time before moving house (if it ever happens...)

Thoughts ?

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