Sanity check - new boiler sizing

[wobbin]

Hi all,

Just wanted to ask the RGI's here - roughly what Kw rating combi boiler would you recommend for a 4 bedroom house with 12 radiators and one bathroom (+one shower room with a cold feed electric shower).

House is a 2 storey corner property with a (2003 vintage and well insulated) ground floor extension.

Currently on a Potterton Profile 50e circa 1988 vintage that is soldiering on, but looking to cut the gas usage if possible.

T.I.A

Cheers
Robin

 

[ScottishGasMan]

Any combi size would do 12 radiators "typically" you really size a combi on your hot water flow rate that your after, 30kw is an average for decent hot water, but that's down to what you consider a decent hot water flow rate.

But don't be so quick to jump down the combi route, if the boilers on an open system and is a heat only would you have anything against just replacing the boiler with a condensing oven vent or system only boiler? Keeping the use of your current hot water cylinder and making the installation cheaper while still improving efficiency, this setup would require more in the way of sizing the boiler depending on the heat loss of the house, say in the range of 12 to 18 kw

 

[Jackrae]

Also consider that the amount of gas you wouldn't save if you didn't change your boiler would cost £x per annum. A new boiler will probably cost 20 times £x to buy and install and at best might last 10 years and save only about 20% (at the very best) of your gas bill before requiring major repair parts.

The economy argument for changing boilers (capital costs) to save gas (revenue costs) versus soldiering on with something that has worked for donkeys and will be capable of doing so for many years is seriously flawed.

Putting it another way, upgrade to a modern "efficient" boiler only when what you have develops a major high cost fault.

 

[DP]

Upgrade controls so you have independent control of hot water and central heating zones (when heating selected, hot water stays off), have three zones even (bedrooms, living rooms and HW cylinder).

Another option is Honeywell Evohome that turns the installation into a multi zone system.

Getting proper service on the boiler is good move too (a service is cleaning heat exchanger, burner etc and cannot be carried out without opening up the boiler

 

[Phill Peck]

Also consider that the amount of gas you wouldn't save if you didn't change your boiler would cost £x per annum. A new boiler will probably cost 20 times £x to buy and install and at best might last 10 years and save only about 20% (at the very best) of your gas bill before requiring major repair parts.

The economy argument for changing boilers (capital costs) to save gas (revenue costs) versus soldiering on with something that has worked for donkeys and will be capable of doing so for many years is seriously flawed.

Putting it another way, upgrade to a modern "efficient" boiler only when what you have develops a major high cost fault.

Posts like this damage our industry.
"At best might last 10 years" ? Where do u get this information from. I regularly get customers say this to me. "Oh no I don't want to replace my leaking 30 year old boiler, those new ones won't even last 10 years"

Descent boiler, descent installer and will easily do 15-20

 

[Agile]

I have to say that most condensing boilers fitted after 2005 when they became mandatory have probably already been replaced by now.

Very unfortunately some boiler models were not reliable and have failed well within the 10 years.

An example of those which have mostly failed is the Ideal Isar/Icos range and many Glowworms.

An example of a reliable boiler which are mostly still in service is the Biasi M96.

But the boiler model is only part of the problem. Fussy homeowners who wanted a cheap installation have engaged installers who did not properly clean the system or spend to have it cleaned or maintained will have mostly had to replace their boilers well within the 10 years.

There are just a few models which are likely to be the best but they cost more than the budget boilers.

Tony

 

[muggles]

As above, keep your existing boiler - the cost of replacing it with a combi will never ever pay for itself in terms of saving on gas usage.

Improve your controls and insulation

 

[Phill Peck]

Tony I doubt most boilers fitted after 2005 have been replaced already

Some I agree and mostly the models u mention.

Only steamers I've removed are

ideal icos/isar/mini he (loads)
Potterton promax (4/5)
Probably some others but they are the worst of the condensers

I have removed one ecotec 624 but it was working fine just grossly undersized.

Most of the boilers I remove are profiles/wrs/solo etc

 

[wobbin]

Just wanted to say thanks, there are some very good points being made here.

I've just had the gas valve replaced as it was intermittently buzzing when the main burner was on and was driving me mad. A full service was performed at the same time and it's running sweetly once again.

I think I will hold off on the boiler replacement. There's no doubt I could improve the insulation in the roof. I'll also look at the Honeywell Evohome set up.

Cheers all !

Kind Regards,
Robin