British Gas will install free insulation to many of its customers who it supplies both gas and electricity to.

The programme will see dual fuel customers getting a free home insulation survey and a choice of either loft or cavity wall insulation (see the Free Insulation guide).

Whilst installation surveys are usually free the cost of either loft or cavity wall insulation is typically a few hundred pounds.

British Gas research shows customers who fitted insulation and energy efficient boilers saved an average of £322 each year between 2006 and 2010, and saw a 44% fall in gas use.

Cavity wall insulation reduced household gas consumption by a typical 18.3%, energy efficient boilers reduced use by 18% and loft insulation reduced consumption by 13.8%.

Is this too good to be true?

There are catches, however. British Gas has around five million dual fuel customers and a limited stock of 200,000 installations available so anyone interested should register on its website as soon as possible, even though the deadline is 31 May.

Plus, it is only free for those with less than 60mm of insulation already while the size of their loft must be 80m2 or under. The cavity wall is also only free up to 140m2.

Homes with a loft space bigger than 80m2 or walls bigger than 140m2 still won't pay for the free components but they will be charged a top up fee of £5 per square meter to get the rest of the home insulated.

The deal also excludes any scaffolding or specialist equipment that may be necessary.

Gearoid Lane, from British Gas, says: "£1 in every £4 spent on heating our homes is wasted because of poor insulation."

The offer is open to new and existing customers, as long as any switch is complete when users apply for the energy efficiency upgrade.

This may mean switchers won't have enough time to go through the transfer process if the 200,000 installations are snapped up quickly.

If you are considering moving to British Gas purely for the offer, ensure you also factor in the tariff cost when working out the best possible deal.

British Gas also offers free insulation to those over 70 or on income or disability related benefits as standard.

Further reading/Key links

Slash energy costs: Cheap Gas & Electricity
Your rights: Fight Energy Direct Debits
Boiler protection: Boiler Cover