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Calculating Size Of Boiler

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FredPuli43 | 15:07 Mon 28th Jan 2013 | Property
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How is the calculation of boiler size done ? I need a rough idea before calling in any heating contractors. Is it by cubic capacity of rooms? This house is a four bedroom, two being large (about 20 feet by 18) and two ordinary double bedrooms, with a dining room about 16 feet by 12, drawing room 25 feet by 20, office 15 by 15 feet, kitchen 20 by 18 feet and hall. The ceilings are at 8 feet 6. There's a downstairs cloakroom and lavatory but nobody's ever thought to heat that so I'm inclined to exclude it.
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It's far more important to know something about the level of insulation in all aspects of the property, Fred, as you will know from your physics O-level that heat in a well-insulated device like a thermos doesn't escape very quickly.
I'm talking walls (cavity insulated?), roofs (lots of Celotex?), windows and doors (DG installed?), and to a lesser-extent floors (assume zilch unless built in the last 30 years).
Boilers come in big jumps between size models. If it is detached but reasonably-well insulated, I would guess around a 30kW output model. Better to oversize a bit in case you extend the house later. You heating technician will be able to assess this on site.
The lengthy method is measure volume of rooms,Allowance for heatloss through windows. subtract windows whether they are single/double/triple glazed. Plus a lot of other factors.What the outside walls are made of. North/South facing
Cavity insulation. Solid/suspended wood floors Thickness of.loft insulation. Loads of things. This will give you output of radiator required for each room. Add in hot water requirement.
A very lot of calculations, but most dont bother these days, If a rad fits under a window that will do attitude.
Any good heating contractor will or should come to the right size of package.If he tells you within 5 minutes of surveying your house call someone else.
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BMate, I either failed O level physics or wasn't allowed to take it (I forget which) but I do watch Brian Cox. Is that any good?

The house has cavity wall insulation and layers of loft insulation but the windows don't permit of double glazing; have to make do with secondary glazing because the windows are all leaded lights. The floors are nearly all solid oak strip downstairs and ordinary deal upstairs.

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Calculating Size Of Boiler

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