How to size a new gas boiler

cubix

What to do a few calculations for a new condensing gas boiler and wanted to confirm what I need to check to size it correctly

Standard 3bed semi
Room size, width X Length x height
Various rad sizes
DHW standard insulated 36"x18"

Houses in the estate are 18yrs old and BER:D1. This should go up slightly on this one to say C1-C2 as in the process of fitting a 100mm internal kingspan slab on all inner external facing walls. Attic has the standard 300mm fibreglass insulation

Dtp1979

cubix wrote: »

What to do a few calculations for a new condensing gas boiler and wanted to confirm what I need to check to size it correctly

Standard 3bed semi
Room size, width X Length x height
Various rad sizes
DHW standard insulated 36"x18"

Houses in the estate are 18yrs old and BER:D1. This should go up slightly on this one to say C1-C2 as in the process of fitting a 100mm internal kingspan slab on all inner external facing walls. Attic has the standard 300mm fibreglass insulation

Save yourself the hard work of calculating. An 18kw boiler is more than enough. I've an Ariston clasHE boiler and with those you can set the output. I've mine set at 10kw which is over doing it a bit too. Similar house to yours

cubix

Cheers, when you can scale the outuput up/down is that to do with the gas valve being modulating. IF so do any of these other brands have a modulation gas valve. I will most likely be fitting a system boiler with three zones, I am leaning towards a WB from a brand/ price balance or can the others be justified. I haven't been into Precision Heat in a while but from there site I would be needing the below one, can anyone confirm the average walk in price or is their website near the mark. Any suppliers have good summer deals on at the moment for WB

Vitodens 100W €1500+vat
Greenstar i System (9kW to 24kW), would the average be €900+vat
Vaillant Ecotec 618 €?

Just to throw a curve ball in, will most likely be putting a new single storey kitchen ext on at some point, the one where you dont need planning (think its 40Sq mtr). Was going to have this running on an UFH via a branch off on a manifold. Would I need to allow much more KW's

Dtp1979

cubix wrote: »

Cheers, when you can scale the outuput up/down is that to do with the gas valve being modulating. IF so do any of these other brands have a modulation gas valve. I will most likely be fitting a system boiler with three zones, I am leaning towards a WB from a brand/ price balance or can the others be justified. I haven't been into Precision Heat in a while but from there site I would be needing the below one, can anyone confirm the average walk in price or is their website near the mark. Any suppliers have good summer deals on at the moment for WB

Vitodens 100W €1500+vat
Greenstar i System (9kW to 24kW), would the average be €900+vat
Vaillant Ecotec 618 €?

Just to throw a curve ball in, will most likely be putting a new single storey kitchen ext on at some point, the one where you dont need planning (think its 40Sq mtr). Was going to have this running on an UFH via a branch off on a manifold. Would I need to allow much more KW's

Any A rated boiler will modulate down. But on its initial firing it will overfire. For instance if you fitted a 24kw boiler it would eventually modulate down but a lot of wasted gas in between. That's the problem with oversizing. Ariston's can be set to limit the output. My boiler is a 24 kw but set way lower so it never fires at 24. I'm not sure if other boilers can do this. 18kw will cover you for your extension too.
If your heart is set on one of the boilers above then go with Worcester bosch. Viessmann are completely overrated and over priced for what they are. They're nothing special TBH.

cubix

What kind of money for a Ariston clasHE

Dtp1979

cubix wrote: »

What kind of money for a Ariston clasHE

Around 900 incl vat. But honestly they should be priced the same as Worcester bosch and in my honest opinion they're a better boiler than the bosch. 8 year warranty too.

cubix

Sounds very reasonable, will have to do a ring around next week.

Dtp1979

cubix wrote: »

Sounds very reasonable, will have to do a ring around next week.

Get your installer to purchase it and make sure he/she is familiar with these boilers. A lot of guys avoid them because they are clueless when it comes to setting them up. Cheaper boilers just need to be switched on and away u go after the combustion readings are ok

Calahonda52

cubix wrote: »

Just to throw a curve ball in, will most likely be putting a new single storey kitchen ext on at some point, the one where you dont need planning (think its 40Sq mtr). Was going to have this running on an UFH via a branch off on a manifold. Would I need to allow much more KW's

Not the best idea.