You may already have this covered, but I though I'd mention it.
Have you already ensured that the insulation is up to scratch, especially in a bungalow?
Min 260mm attic insulation - 100mm between the joists and 160mm laid across the joists.
Insulation in the walls - if cavity, then has it been blown in
All windows at least double glazed.
All draughts have been stemmed, e.g. external doors draught sealed, fireplaces blocked up if/when not being used.
Also you may consider (since it is easier to retrofit in a bungalow) ventilation with heat recovery (note: I am not talking about heat generation, just recovering the heat lost when ventilating the house). This is only if you want to go the full 9 yards.
You only need to heat the house with as much as is being lost. If you can stem any losses, then you may not need as much heat, and your range may be adequate.
Again, this may not be an issue if the house is fairly new, but thought I'd mention it.