Why insulation is the best first investment
Before upgrading your heating system, insulate the building envelope. A new heat pump in a poorly insulated home is like heating the street — expensive and ineffective. Insulating your loft and walls first makes every heating upgrade more effective and delivers immediate energy bill savings.
Loft insulation
If you have less than 270mm of loft insulation (or none at all), topping up is the single cheapest and most effective energy improvement available. Installing 270mm of mineral wool insulation costs £300–£600 for an average semi-detached. Government grants are frequently available through energy suppliers' Energy Company Obligation (ECO) scheme — you may be eligible for free insulation.
Cavity wall insulation
Homes built between 1920 and 1990 typically have unfilled cavity walls. Filling them with mineral wool or blown bead insulation costs £400–£800 for a typical semi. This can reduce heating bills by 15–25%. It is not suitable for all properties — walls exposed to heavy driving rain, or those with problems with the cavity (wall ties, damp), should be assessed first.
Solid wall insulation
Pre-1920 solid-wall homes are the hardest to insulate. Options are external wall insulation (insulation board applied to the outside and rendered over — costs £8,000–£18,000 for a semi) or internal wall insulation (losing 50–100mm of room depth per wall — costs £5,000–£12,000). Grants are available for eligible households. The savings are significant — 25–40% reduction in heating bills.