A survey of 2,000 UK adults in a relationship found more than three quarters (79 per cent) were surprised by some aspects of their partner's behaviour when they shared a home for the first time.
And it was their other half’s attitude towards sustainability inside the home which they were most likely to take issue with.
The biggest surprise was how they would leave lights on when not in the room, followed by snoring, leaving appliances plugged in when not in use and putting the recycling in with the black bin waste.
Other discoveries included finding out that they didn’t tidy up after themselves, left the heating on unnecessarily, wasted food and opened the window despite the boiler on full flow.
As a result, 54 per cent of couples are encouraging each other to be more sustainable - with 27 per cent claiming their attempts to live a greener life has brought them closer together as a couple.
The research was carried out by BT, which is giving households the knowledge and motivation needed to make small but sustainable lifestyle changes and highlighting the role technology has in making the shift to sustainable living easier.
It also found a third of adults are doing more than they were 12 months ago to live a greener life at home.
Overall, 78 per cent of those surveyed regard sustainability as important to them as an individual.
When asked which ‘climate resolution’ they would make to live a greener life, switching to an electric vehicle emerged as the top choice, followed by recycling as much as possible and only using the heating while necessary.
Making up the top five were switching to a renewable energy provider and eating more plant-based food.
It also emerged more than two thirds of respondents who have smart tech in their home feel it has helped them be more environmentally friendly.
However, 68 per cent of those polled via OnePoll wish they could use less energy each month, with just a quarter of people in a relationship aware of how much energy their household uses each month.
The results come after BT recently announced the results of its Smarter Living Challenge [https://www.hubbub.org.uk/bt-smarter-living-challenge] - a partnership with environmental charity Hubbub to highlight the impact households can have on their carbon emissions by using technology to support simple sustainable lifestyle changes.
Andy Wales, chief digital impact and sustainability officer at BT said: “We want to show people up and down the country that it’s not just politicians and corporations who can make a difference in the fight against climate change: everyone has a part to play.
"That’s why we’re encouraging our customers, colleagues and communities to make their own ‘climate resolutions’.
“We’re committed to helping people improve their digital skills at home, providing them with the knowledge and motivation needed to make small but significant changes in their life with the help of technology, and help them lead a more eco-friendly lifestyle.”
TOP 30 'SURPRISES' ABOUT A PARTNER AFTER MOVING IN WITH THEM
1. Leaves lights on when not in the room
2. Snores
3. Leaves appliances plugged in when not in use
4. Puts recycling in with the black bin waste
5. Doesn't tidy up after themselves
6. Leaves the heating on unnecessarily
7. Wastes food
8. Opens the window with the heating on
9. Leaves the TV on when leaving the room
10. Wastes water
11. Leaves the toilet seat up
12. Watches the TV really loudly
13. Never puts the washing away
14. Never rinses out the sink after brushing their teeth
15. Leaves cups/glasses all over the place
16. Hair seems to fall out everywhere
17. Never makes the bed
18. Uses lots of water when hand washing dishes
19. Puts one item in the washing machine and runs a cycle
20. Showers for ages
21. Always needs attention rather than letting you have 'me time'
22. Careless with food/drink on furniture
23. Hides the smart energy meter / turns it off / Checks the smart energy meter every day
24. Is a terrible cook
25. Always puts a load of washing in the machine but never hangs it out to dry
26. Shouts /screams when watching sports
27. Chews really loudly
28. Doesn't empty /load the dishwasher
29. Puts the dishwasher on before it’s full
30. Makes lots of noise in the morning