This sounds an awful lot like a Seinfeld plotline. But, obviously, this is real life. My first inclination was to suggest that you write your partner a $180 check for a year’s worth of extra electricity use. Then you can turn on the bathroom heater before your morning shower guilt-free. But I suspect we’re not really just talking about an extra $15 a month on the electric bill here, are we?
Managing money alone is hard enough. Try doing it with another person -- someone who has their own financial baggage … their own way of doing things and ideas about how to spend, save and invest -- and things quickly go off the rails.
Since preserving your long-term relationship is critical, you have to approach your problems like partners, not adversaries. So while I agree with you that he’s “won” this electricity use competition (because, let’s be honest my friend, he’s playing to win), what's more important is that you both get something out of this running tiff. I suggest you use it as a springboard for a more in-depth discussion. Focus on the things that REALLY matter to the health of your relationship -- financially and emotionally.
Here’s your homework:
Air your dirty laundry -- but be civil about it, please: Take turns talking about your biggest and most sensitive financial concerns. Talk about what matters to YOU, not what you think should matter. Be concrete and as specific as possible. For example, instead of saying "I get worried about what we have in the bank,” spell out what you envision: "I'd feel a lot more secure if we had $3,000 in our emergency fund.”
Stop sweating the small stuff and go big: Sit down together and come up with a list of larger money goals. Not just “an electric bill that’s $40 a month,” but something more aspirational. Highlight the places where your goals overlap (e.g. saving up to buy a yurt or an electric car or even a yearly savings target).
Look forward: Yes, the past matters. But more important is what you do from this day until death do you part. Pick goals that keep you both jazzed about what's in store for your relationship. Plan your vacation, early retirement or home addition. Then map out the money details that will get the job done -- like how much you need to save each month -- and start tracking your progress. When you have goals to keep you excited, that makes dealing with the daily money struggles (and the fight over the thermostat) a lot easier.