New Gas Boiler

Archergirl

We are going to get a new gas boiler as ours keeps breaking down so decided to bite the bullet.
We have a 15kw at the moment and 8 rads ( but one is a double) 15kw apparently do up to 10 rads.
Would it be more cost effective to get a bigger boiler that won't have to work so hard or just get another 15kw one. We will be getting it from British Gas to take advantage of the 5 yr interest free offer.

tim_p

I’d be getting a local installer or three to quote as well. Whilst the interest free offer is probably good, it’ll be interest free on a grossly inflated install price.  A typical like for like replacement ought to be around £1500-£2000 or possibly less. Going up in output might require larger internal pipe work so make sure things like that are factored in. 

QrizB

Therre's no point getting a bigger boiler, your radiators can only put out so much heat. You might even be better with a smaller one.

Measure your rads and look for similar sized ones at eg. Screwfix then add up their wattages. Unless your eight are huge it's unlikely that they'll add to more than 10kW or so.

For comparison I'm in a 3-bed semi with an 18kW boiler but my nine rads add up to around 11kW.

Astria

It's not just the number of rads, it's the amount of people in the house wanting hot water for things like baths, showers, etc, as well and what kind of flow rate you require to those devices. Also, combi or regular? I prefer regular as it's then simply a water heater, but a lot of people prefer combi's.

Don't forget that other companies that sell boilers may not do interest free years, but the overall price may be less, so the end result could be cheaper too!

Archergirl

Astria said:

It's not just the number of rads, it's the amount of people in the house wanting hot water for things like baths, showers, etc, as well and what kind of flow rate you require to those devices. Also, combi or regular? I prefer regular as it's then simply a water heater, but a lot of people prefer combi's.

Don't forget that other companies that sell boilers may not do interest free years, but the overall price may be less, so the end result could be cheaper too!

Only two of us and one bathroom with an electric shower, I thought they were all combi boilers now, the one we have is a regular one and I thought they guy said they were starting to do only combi when we got it (2005)
I realise we can get it cheaper and we do have the money to pay for it but I would rather use it for other things hence the 5 yr % finance.

tacpot12

Most moderm boilers can be set to produce less heat than their full rated output when operating to heat the home. Most will also reduce (modulate) their output if the return water coming back from the radiators is still hot.

If you are having a combi boiler, I would get one that has 24kW+. If you are having a boiler that is going to heat a hot water tank and operate your  central heating, you should be fine with a 18kW boiler. 

Archergirl

tim_p said:

I’d be getting a local installer or three to quote as well. Whilst the interest free offer is probably good, it’ll be interest free on a grossly inflated install price.  A typical like for like replacement ought to be around £1500-£2000 or possibly less. Going up in output might require larger internal pipe work so make sure things like that are factored in. 

I didn't think of bigger pipework, good point. I realise the install is expensive we have been quoted 2.2k  which I thought was a reasonable price I know the installation will be more with BG but sometimes you can get into trouble with smaller companies I know you could with BG as well, but easier to get things put right maybe.

QrizB

Archergirl said:

Astria said:

It's not just the number of rads, it's the amount of people in the house wanting hot water for things like baths, showers, etc, as well and what kind of flow rate you require to those devices. Also, combi or regular? I prefer regular as it's then simply a water heater, but a lot of people prefer combi's.

Don't forget that other companies that sell boilers may not do interest free years, but the overall price may be less, so the end result could be cheaper too!

Only two of us and one bathroom with an electric shower, I thought they were all combi boilers now, the one we have is a regular one and I thought they guy said they were starting to do only combi when we got it (2005)
I realise we can get it cheaper and we do have the money to pay for it but I would rather use it for other things hence the 5 yr % finance.

Replacing a regular boiler with a combi is a bigger job, unless you add the HW tank as a zone on the CH circuit (in which case you're running it like a regular boiler anyway). Sticking with a regular one should be cheaper and quicker to fit.

And, despite what your last guy said, regular boilers are still a big product line from all the major manufacturers

tacpot12 said:

Most moderm boilers can be set to produce less heat than their full rated output when operating to heat the home. Most will also reduce (modulate) their output if the return water coming back from the radiators is still hot.

Therre's a limit as to how low they can modulate, which is why sizing is important.

[Deleted User]

In my experience, installers will sell you whatever you want in terms of size etc. Have a look at this link to a paid service that offers professional advice. 

https://www.theheatinghub.co.uk/how-we-work

(Disclaimer: I have no link to this site or its advisers)

Archergirl

QrizB You are quite correct, we have been offered either a Vaillant ecoTec Plus or a  Vaillant Eco Fit Pure both are regular boilers....... 

Reed_Richards

I would get a boiler with Opentherm (standard) capability and a controller to match.  This will give you the best control and hopefully the best economy of operation as Opentherm does both Weather Compensation and Load Compensation.