Boiler sizing

[Hobo128]

Been to see a job recently. The customer is planning on have a loft conversion with an ensuit.
At the moment it is a 4 bedroom house with a bathroom and ensuit. There are 10 rads in the house. The ensuit has a shower that works of the boiler and the main bathroom has a bath and electric shower.

The new proposed ensuit will have an electric shower and a bath, basin and towel rail. The new proposed 5th bedroom will at most have two radiators.

They want to keep there existing boiler which is about 6 years old but is a worcester greenstar 30si

To me this boiler is undersized for the property let alone the new proposed work to be done.

I am tempted to go down the unvented route with this or something like a high flow.

What does anyone think?

 

[chris watkins]

Can I humbly suggest that you get yourself a copy of this design guide. CIBSE - Domestic Heating - Design Guide 2015 (Domestic Building Services Panel)

It will enable you to answer most of the heating design questions you have been asking, it is probable one of the best technical books I have ever seen & worth every penny of the £28 to a pro heating installer.

I am on my third edition.

You simple can't guess on heating requirements you need to do the heat loss calculations.

 

[macackau]

If that's just a heat only boiler that'll put out enough heat to heat the current house and the next door neighbours. Heat loss calculation will show just how little is actually needed. Amount of times I go to a largish property and the installer has panicked and thrown in a huge 30kw boiler when In fact they could have put in something like a 15kw.

 

[chris watkins]

If that's just a heat only boiler that'll put out enough heat to heat the current house and the next door neighbours. Heat loss calculation will show just how little is actually needed. Amount of times I go to a largish property and the installer has panicked and thrown in a huge 30kw boiler when In fact they could have put in something like a 15kw.

Does it make any difference if you install an oversized boiler ? You bet your bottom dollar it does,
the boiler electronics are system size related, so things like the amount of heat the boiler puts into the system when it fires for the first time each heating period differs in each, along with the minimum boiler heating rate etc.

Some think that just because a boiler is fully modulating it must be ok if I just spend over the odds getting a bigger boiler because I can't be assed to size it correctly.

 

[magicno1]

30si is a combi...... In a house this size?????

 

[macackau]

30si is a combi...... In a house this size?????

Keep the combi for the kitchen sink and install and unvented cylinder