Nine times out of ten it’s one of five fixable causes — and the biggest is above your head, not in your radiators.
Heat rises into bedrooms then straight through a thin loft. Under 270mm of insulation, upstairs acts as a chimney for the whole house. The fix is the cheapest in home energy: a ~£750 top-up — often funded.
Unbalanced radiators starve the last-in-line bedrooms (a free lockshield adjustment). TRVs set low or stuck. Room-in-roof spaces lose heat through uninsulated slopes (fix). Loft-hatch and window draughts dump cold air upstairs first — £20 of sealing.
Run the Heat Loss Calculator — it scores roof, walls, floors and draughts for your actual home and orders the fixes by impact.
AC-coupled (battery has its own inverter) is the retrofit default: no rewiring of your array, works with any brand or age of system, £3,500–£6,000 installed for 5–10kWh usable. DC-coupled only makes sense if your inverter is due replacement anyway — a hybrid inverter + battery swap can be cheaper combined.
Feed-in Tariff payments are unaffected by adding storage — generation payments continue and deemed export isn’t metered down. On SEG, a battery lets you shift export into peak-price windows instead.
Match usable capacity to your evening consumption and summer surplus — the sizing guide has the tables. Most 4kWp homes land at 5–8kWh usable.
Usually thin loft insulation letting risen heat escape, plus unbalanced radiators. Check insulation depth first — under 270mm is your answer.
Only if the loft holds it. With poor insulation, rising heat exits through the roof and upstairs feels coldest.
Radiator balancing (free), draught-sealing (£20), then the loft top-up (~£750, often funded).
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
Free, independent, 60 seconds. We compare every option, check Government scheme eligibility and match you with one trusted local installer if you want one.
Check My Home →