I think that it's the dedicated room that makes a different tax wise. It depends on why you're asking - for tax reasons I imagine? If the business, or you as a sole trader, is registered to your home address, then I guess you are running a business from home. If you're a limited company and it's registered to your home address, then you're definately running it from home.
If it's for mortgage or rent purposes - if you haven't got customers coming to your house, I'm sure you're allowed under a domestic mortgage or rent agreement to run a business at home. I've worked from home before as a journalist and there didn't seem to be any problems.
I can't give professional advice but this is what I've gathered over the years. I guess other answers would depend on why you're asking.
I hope your business is booming!