British Gas is offering free cavity wall or loft insulation to its dual fuel customers.
The deal includes a free survey and installation.
Customers must register by 31 May and the offer is limited to 200,000 installations. British Gas is investing up to £80 million in the free offer.
British Gas also offers free insulation to those over 70 or on income or disability related benefits.
Terms and conditions apply.
Customers should log onto http://www.britishgas.co.uk/freeinsulation