What is the seasonal efficiency of the Wessex ModuMax mk3 boiler? Hamworthy Heating September 06, 2018 09:48 Updated Follow The Building regulations Part L seasonal efficiency data can be found on pages 8-9 of the technical sales brochure or on the 'Technical data' tab on the product page. Download the product brochure. Related articles What are the NOx emissions of the Wessex ModuMax mk3 boiler? How long will delivery take? Comments 0 comments Please sign in to leave a comment.