replacing back boiler system

[Nis]

Hi folks,

I am thinking of changing my ancient back boiler heating system (gravity based, pumped). The reason is to get instant hot water, reduce bills and stop the hassle of pilot lights going out or wasting gas etc.

The options that i have include

1) Converting to a fully pumped system. I asked one guy about likely costs and he quoted me 'thousands'. Also, a fully pumped system won't get me instant hot water although the new boiler would probably save money on gas bills.

2) Just bin the old back boiler and invest in a combi (or condensing combi). However, since my property is 'large-ish' (3 bedroomed terrace, with additional 2 bedrooms in loft, 1 bathroom) - i'm worried if a combi can cope with it. I certainly dont want cold rooms in the loft! Price wise, i reckon i can get the boiler for around =A3600 and get it installed for another =A3600-ish. This compares favourably with option

1) above.

Do i go for a high output 30HE condensing boiler, since this seems to be more powerful than other 24HE boilers, or will a standard non-condensing combi do the job?

Advice appreciated. Ta.

[Ed Sirett]

I think the Boiler Choice FAQ may help you, see Below. Almost certainly the worst thing you can do is to replace the existing back boiler with an updated model. Such units are expensive and not very efficient. You probably could get a condensing boiler exception for this location but you should still think it worth upgrading.

The £600 might be a price for exchanging a combi boiler with another one of a similar type in a similar location. Converting from the exitsing back boiler will likely cost a bit more.

[Mark]

Without knowing the heat loss from your house I can't be 100% sure, but normally a suitable combi would have no problem heating a house your size. The power output of the boiler is more a limiting factor for hot water not heating.

A sealed heating system would mean you could lose your loft heating header tank and with a combi boiler you could lose the cylinder, which could save some space.

If you need quick filling baths however a combi boiler may disapoint.

To meet building regs most new boilers need to be condensing but you may be exempt.

Mark

[Roger Mills (aka Set Square)]

Combi boilers are usually sized according to what rate of 'instant' hot water production you want to achieve. If you go for one powerful enough to fill a bath - when timed with a stopwatch rather than a callendar - it won't have any trouble with the space heating.

Note that you may need to upgrade your gas supply pipes. Also note that a combi is only viable if you have good mains water pressure and flow. Measure the rate of cold flow at your kitchen tap with a bucket and stopwatch. If it's less than 20 litres/minute, you're going to be struggling.

[John Rumm]

Yup, I agree with what Ed, Roger, and Mark have said. I would add also don't underestimate the improvement you can have with a well designed storage system. A good fast recovery cylinder and well designed controls on the boiler should see you being able to draw off another bath within ten minutes or so recovery time.

If you do decide to go the combi route, also bear in mind that it can also be used to heat stored water. So you can have the advantages of both if you require - massive flow rates to the baths from the storage system, and mains pressure instant hot water to showers etc.

If you want acceptable "instant" hot water performance from a combi I would suggest 35kW as the minimum power output to go for.

[David Hansen]

On 3 Feb 2006 06:48:39 -0800 someone who may be "Nis" wrote this:-

[snip]

A new boiler and fully pumped system will not get you "instant" hot water. However, if you have a properly insulated hot water cylinder then hot water will always be available, unless the cylinder is emptied of it. With a high recovery cylinder getting enough hot water for a sink will only take say 10 minutes anyway.

A properly selected combination boiler will have no problem heating all the rooms. The question is over hot water. How many people are normally in the house? Do any of the bedrooms have basins/showers in them? Do you plan more bathrooms or washing facilities in the bedrooms? In a large household with lots of hot water use combination boilers are often not the best option.

ps the best way of saving gas is to insulate the walls and loft, if that has not been already done.