The Garfield Weston Foundation is one of the UK's largest independent grant-makers, distributing around £80 million a year. It is not a church-specific funder, but churches are among the organisations it supports regularly, particularly for capital projects that benefit the wider community.
Heating installations and energy efficiency improvements qualify as capital works. The foundation has funded church heating projects in the past, typically where the church can show the building serves the community beyond Sunday worship. If your church hosts community groups, food banks, concerts or other activities, that strengthens an application considerably.
Regular grants range from around £5,000 to £100,000. Major grants above £100,000 are available but are competitive and tend to go to larger, multi-phase projects. The foundation does not fund routine maintenance, running costs or retrospective work. Your project should be clearly scoped with a realistic budget and, ideally, some funding already in place from other sources.