Sash Window Draught Proofing Calculator

Select draught proofing system and see installation costs, annual heating savings, and payback period. Estimates based on 2026 UK contractor rates and Energy Saving Trust data.

Draught Proofing Systems Compared

Basic Brush Seals (£140 per window)

Nylon pile brush seals fitted to staff bead (inner frame) and parting bead (between sashes). Self-adhesive or pinned. Allows sash to slide while blocking draughts. Reduces heat loss by 25-35%. DIY kits available (Reddiseals, Mighton) £30-£50 per window. Professional installation takes 2-3 hours. Lifespan 8-12 years before pile wears flat.

Compression Seal System (£200 per window)

Silicone or EPDM compression seals fitted in routed grooves in staff bead, parting bead, and outer frame. Sashes adjusted for tight fit. Creates compression seal when closed. Reduces heat loss by 35-45%. Requires router and precision fitting (not DIY-friendly). Lifespan 15-20 years. Quieter operation than brush seals. Can accommodate slight sash movement.

Full Overhaul with Seals (£280 per window)

Complete service: remove sashes, replace all 4 sash cords, fit compression seals, adjust sash weights, ease sticking points, lubricate pulleys, test draught seal with smoke pen. Reduces heat loss by 40-50%. Combines energy efficiency with mechanical refurbishment. Sashes operate like new. Lifespan 20-25 years before seal replacement needed. Best value if cords are broken or sashes stick.

Annual Heating Savings

Draught proofing one sash window saves £60-£120 per year in heating costs. Savings vary by:

• Window size: Standard (1.2m × 1.5m) saves £60-£80/year, large bay window (2m × 2m) saves £100-£120/year
• Seal quality: Basic brush seals save 25-35%, compression seals save 35-45%, full overhaul saves 40-50%
• Exposure: North-facing, exposed properties save 20% more than sheltered south-facing
• Heating type: Gas heating (7p/kWh) saves £60-£120, oil heating (9p/kWh) saves £80-£155, electric heating (24p/kWh) saves £200-£300

Energy Saving Trust estimates draughty sash windows lose 10-15% of household heat. Draught proofing 10 windows in a Victorian terrace saves £600-£1,200 annually. Installation cost £1,400-£2,800, payback period 1.2-4.7 years.

Payback Period

All systems pay for themselves within 3 years. Over a 15-year lifespan, basic brush seals save £900-£1,200 per window, compression seals save £1,200-£1,500, and full overhaul saves £1,500-£1,800. These are net savings after installation cost.

DIY vs Professional Installation

DIY draught proofing costs £30-£60 per window in materials (Reddiseals, Mighton kits). Takes 2-4 hours per window for a competent DIYer. You save £110-£220 in labour per window. Total DIY cost for 10 windows: £300-£600 vs £1,400-£2,800 professional.

Professional installation recommended if:

• Sashes need adjustment or easing (requires hand planes, spokeshaves, patience)
• Cords are broken (need to remove sashes, access weight pockets)
• You want compression seals (requires router, precision fitting)
• Property is listed (conservation officer may require reversible professional installation)

DIY suitable if sashes operate smoothly and you're fitting brush seals only. See our draught proofing cost guide for step-by-step DIY instructions.

Sources

Draught proofing rates and savings verified against:

• Checkatrade sash window draught proofing quotes (Jan 2026, 10 specialists, London/Southeast)
• Energy Saving Trust heat loss studies for single-glazed sash windows (2025)
• Reddiseals, Mighton Products, Ventrolla trade price lists (Jan 2026)
• Historic England energy efficiency guidance for period properties