Roommate has a problem with me working from home 2-3days?
Most utility consumption would happen anyway. Appliances, HVAC, etc., the big lines on the utility bill, operate the same no matter how many people are home. It's not like you can leave your refrigerator and freezer off when you're away from the house! Stuff like lights being on is a tiny, incidental item on a utility bill, especially with more efficient modern lighting. And you may not even use that during the day. Sunlight is free. So unless the work you do at home involves you running high draw electric tools or the like, you are not appreciably increasing the utility bill from it.