Summary & Technical Highlights
How to size a combi boiler for Victorian Glasgow flats with high ceilings. Heat loss calculations, radiator sizing, and bathroom hot water demands.
✓ Fully verified against current Scottish Building Standards & Certified Heating Regulations.Overview & Key Takeaways
Most online boiler sizing tools use an oversimplified metric: *count your bedrooms and bathrooms*. For a 1990s suburban semi-detached house with 2.4m ceilings and cavity wall insulation, this is adequate. For a Glasgow tenement flat with **3.2-metre high ceilings, uninsulated 600mm sandstone external walls, and tall timber sash windows**, this rule results in undersized boilers that struggle to heat rooms in winter.
Calculating Cubic Air Volume in Tenements
To calculate heat loss accurately, multiply floor area by ceiling height: - Modern 2-Bed Flat (65 ^2$ \u00d7 2.4m height): Air volume = 156 ^3$ - Glasgow Tenement 2-Bed (75 ^2$ \u00d7 3.2m height): Air volume = 240 ^3$
A 2-bedroom tenement contains over 53% more air volume than a modern flat with an identical floor plan.
Sizing Matrix for Glasgow Tenements
| Tenement Property Profile | Radiator Count | Recommended Central Heating (CH) Output | Recommended Domestic Hot Water (DHW) Output | Ideal Boiler Models |
|---|---|---|---|---|
| 1-Bed Tenement Flat (Internal) | 5 \u2013 7 Radiators | 18kW \u2013 20kW | 28kW \u2013 30kW | Ideal Logic+ 30, Baxi 600 30 |
| 2-Bed Tenement Flat (Corner/Top) | 7 \u2013 10 Radiators | 22kW \u2013 26kW | 30kW \u2013 32kW | Worcester 4000 30, Navien NCB500 32 |
| 3-Bed Tenement Flat (Grand Bay) | 10 \u2013 14 Radiators | 28kW \u2013 32kW | 32kW \u2013 36kW | Worcester 4000 35, Vaillant ecoTEC 34 |
| 4-Bed Main Door / Townhouse | 14+ Radiators | 30kW+ (or System) | 36kW \u2013 40kW (or Unvented Cyl) | Worcester 8000 Life, System + 250L Cyl |
Heating Load vs Domestic Hot Water Priority
Modern combi boilers feature split ratings: central heating output and domestic hot water output. Even if your flat's thermal radiator load requires only 20kW of continuous central heating, you still need minimum 30kW to 32kW of instantaneous hot water power to maintain a 12 to 13 litre/minute shower flow rate when Loch Katrine reservoir supply temperatures drop to 4\u00b0C in January.
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For sandstone tenements and high-ceiling flats across Glasgow, book a specialist tenement boiler installation, upgrade with a direct drop-in tenement boiler replacement from £1,299, or schedule an engineer for a fixed £90 Glasgow boiler repair.
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