Stockton 3 - Key Facts Overall domensions 389 x 510 x 338mm (w x h x d) High efficiency heating Wood: 77% - Smokeless Fuel: 86% Multi-fuel (with external riddling). Approved for Smoke Control Areas. Cleanburn. Airwash. Maximum heat output 3.75kW. Maximum log length 200mm. Flue connection 128mm 5" top or rear Choice of four colours.