Here are some things that make you home cooler in winter
Clearly you do not want to cool your home in winter, it is your job to identify which of these you have and then to reduce their effect.
Cavity walls
Dot and dabbed walls linings
Ventilated underfloor voids letting draughts into your home
Cavity party walls
Extractor fans
Trickle vents
Badly fitted floorboards
Missing floorboards under kitchen units
First floor voids let draughts in from outside cooling both ceiling and floor above
Dormer bungalow first floor voids onto loft
Letterboxes
Sliding sash windows
Open flues
Redundant combustion air bricks
Soil and vent pipe casings
Ventilated chimneys
Thermal bypass in warm roof at gable & eaves roof-wall junctions
Dormer windows
Crittal windows
Cat flaps
Cold water cisterns – the loo one if not the CW tank – importing cold water which gets warmed up by the house.
Drying clothes indoors – latent heat of evaporation is sucked out of the house interior
Drying logs indoors – ditto
Defrosting food from freezer indoors (do this in your fridge)
Bringing anything cold into the house
Single glazed windows
Badly fitted floorboards