Best valiant boiler for 300 Litre tank (6 bed 3 bathroom including loft)

[mrbg07546]

I want valiant because my plumber is a advanced member, and that's a extra 2 year gaurd tee. There's a new green iq system boiler out this week. It's only 27kw. But has modulation to stop the theory of "oversized boiler" which seems to be a hot topic on this forum.

Is 27kw has no risk of being under powered I will get that.

 

[mrbg07546]

I used a heat loss calculator where I specified every room including receptions size. It says kW total 19.3 and 65200 BTU.

I presume a generic heat loss calculator would assume average insulation.