Get a second opinion. Some installers are used to old gas boiler principles where they oversize the system by a factor of 2x or more.
My gas boiler is 30kW for some reason, but a 6kW heat pump would be plenty
Thanks yeah, I've had 4 quotes in total now. All c.£7k. One being £11k, all with the grant. I would pay cash today for a quote below £2k... but alas, not for us it seems.
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My gas boiler is 30kW for some reason, but a 6kW heat pump would be plenty