First don't double post.
Word of mouth is the best form of advertisement.
I've thought about doing what you want to do a couple of years ago. I was going to advertise it as after hours service. "Why take a day off work for the HVAC co. to show up. We're available when you are." Something like that.
I would only start with business cards. Don't waste a lot of money on advertisements. Maybe yard signs as well.
Good Luck.