Advice · Heating design
Are we paying enough attention to the building before deciding how much heating it needs? Understand the building first. Design the heating system second.
Inspired by the Grand Designs episodes “Bletchley” (2021) and “Bletchley Revisited” (2026), this article explores a simple question: are we paying enough attention to the building before deciding how much heating it needs? The episodes examine the use of insulated earth banks and thermal mass to help retain heat.
Every property behaves differently. Geographical region, elevation, exposure, wind shielding, solar gains, thermal mass, airtightness, ventilation and insulation all affect its thermal behaviour. Ground-contact construction deserves particular attention.
For example, with an indoor temperature of 21°C, outdoor air at −3°C gives a temperature difference of 24 K. Ground at an illustrative 10°C gives 11 K. This comparison explains the principle, but actual below-ground heat loss must account for wall depth, soil, geometry, insulation and seasonal conditions.
One of our current projects has a lower-ground floor surrounded by earth, reinforced-concrete construction, substantial insulation and a proposed future garden roof. These features make it an interesting case study in how a building responds to its surroundings.
The proposed heating design uses an appropriately sized air-source heat pump and low-temperature underfloor heating, targeting approximately 35°C flow temperature at winter design conditions. Unlike the experimental seasonal storage concept featured on Grand Designs, this project uses conventional insulated construction. More on this project.
Thermal mass can moderate temperature changes, solar gains can provide useful heat, and airtightness can reduce uncontrolled air leakage. Insulation limits heat transfer. However, solar gains and thermal mass should not simply be subtracted from peak winter heat-loss calculations; they are particularly relevant to comfort and changing energy demand over time.
Efficient heating begins with understanding the complete building and its environment, not just choosing equipment. The aim is a comfortable, efficient system designed around the property's actual needs.
Understand the building first. Design the heating system second.
Disclaimer: This article reflects professional views and is provided for general educational information. Illustrative figures are not a substitute for a property-specific technical assessment or heating-system design.
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