Incorrect Boiler Size

[Extensionwoes]

I have recently, as part of an extension build, had a new boiler installed. I have since been told by another plumber that the boiler is too small. It is a 24kw and his workings mean we need a 30kw. It is a condenser boiler. He used the mears calculator. (It is a 4 bedroomed detatched 1930s house, partial double glazed, no cavity wall insulation (apart from small 3 x 4 metre single storey extension) with loft conversion, big bay windows in 3 rooms)

My question is what rooms should/should not be included in the calculation. The second plumber has included all rooms including hall/stairs/landing and a loft conversion which currently does not have a radiator in it but we lose a lot of heat to (there is no door to close to prevent heat loss).

I am in dispute with the builders over all sort of problems we had with the extension. I have done what they asked and got the plumber to give his calculations but they say the 24kw is right. Any help would be greatly appreciated as to what is right/wrong and where I can take this to next.

 

[Agile]

A 24 kW boiler is almost certainly correct.

You dont say what the effect is but any problems are likely to be caused by too small radiators, a lack of balancing or inadequate pipework sizes.

There are two calculations to be done. The whole house heat loss and simply adding up the heat output of all your rads.

The Mears usually results in an answer over sized by about 20%.

If you have cavity walls then get them insulated as that makes a massive difference to heating costs.

Do you really think you have an actual problem or are you just trying to find points of argument with the builders? I hope that you are not just trying to find excuses not to pay them?

Tony

 

[doitall]

Have to agree with Agile, a 24Kw boiler should eat it.

Undersized radiators and or pipework is another story, and could well affect the heat output to each individual room.

 

[kevplumb]

and have to add was it cleaned out before the boiler was replaced / did it heat ok before

can't see it being undersized i had a 24 kw turbomax in a 5 bed 3 decker and never had to turn it past 7 on 16 rads

 

[Extensionwoes]

I had a couple of radiators changed at the same time and the others checked that they are the right size. Not sure of the size of the boiler before but think it was the same size but downstairs of our house was never warm enough.

The mears shows a BTU of 108,000 - I need clarification please as to what rooms are normally included in this??

Thanks!!

 

[kevplumb]

any that are normally heated

as in you don't count cupboards etc

 

[Extensionwoes]

So the loft (which doesn't currently have a radiator but we lose heat to) should not be included? We have had underfloor heating put into the kitchen but have wooden floors and have just found out that this will not heat the room but will just take the coldness out of the floor. We will now have to install a radiator (or 2) in this room also.

 

[kevplumb]

So the loft (which doesn't currently have a radiator but we lose heat to) should not be included?

ok if you are using it as habitable space its included

 

[doitall]

108000 = 31.6 KW, so still within the capabilities of the boiler.

Underfloor heating is fine under wood if installed correctly, the critical factor is not to have air pockets, they make make steel plates for the pipe to clip into, that should finish flush with the joists. Not that you should need a great deal of heat in a kitchen anyway.

Try to remember the Mears calculators allows for the worst weather, + around 20%.

 

[Extensionwoes]

I'm lost now! 31.6 kw is within the capabilities of a 24kw boiler?

 

[londonboy]

You've employed someone to fit a boiler to warm your house.
I guarantee it warms your house.

Why are you moaning?!
I agree with agiles first reply.

 

[doitall]

Post the size and make of all the radiators, and whether they are single or doubles.

What allowance have you made for hot water.

Can you also post the length and width of the property.

Is it rectangular.

Plus the size of any extensions.

 

[bengasman]

Put the mears calculator where it belongs, bottom drawer, you don't need it. I can work out in 1 minute flat if your current boiler is fine or too small.
Lateral thinking gentlemen! Read the first post, think about it and ask the 2 relevant questions in stead of reinventing the wheel.

 

[doitall]

Know what you're trying to say Ben, but lets have the measurement, and we can work it out our self.

 

[Extensionwoes]

I'll measure the outside of the house in the morning and will post then.

In answer to why I am moaning..... because I have been ripped off by two blokes who have done just about everything wrong in a 3 x 4 metre extension and kitchen fitted. I have paid way over the top to somebody that came recommended by 3 different people. I am bitter yes but I must now take it on the chin and rectify their mistakes. I am no expert and I just wanted a little advice as I have a plumber I trust telling me one thing and the builders telling me another.

Thank you for your replies!