Warm air and cold air returns

[Brianod]

We have a finished basement in our new home completed  by our builder (six months old).  The basement is a walk out and in the main room (550 sqft)  there is only one warm air register. It is just above the floor on an outside wall right beside the walk out sliding glass door. It is also furthest away from the furnace (35ft. ). There is no cold air return in the basement. I've read that there should be one warm air register for 40 sq meters place to distribute the air. We are offside on that but what I want to know is how many registers should there be and should there be a cold air return. The basement is typically more than 5 degrees colder than the main floor temperature. Thanks for any help you could provide.

[Porcupinepuffer]

You definitely need a return air. The existing supply air can't really push air if it's not flowing into a return air to help it out. The air will want to cycle around the easier locations where return airs are present. For your supply air situation, I would have installed at least 2 in a room that size. But this also depends on heat loss with windows, geography,  size of the existing supplies. I'm assuming the one you have is a standard 5".

[Brianod]

Thanks for your reply. Yes, the existing one is 5" and I did think we need a cold air return but also need additional warm air registers.

[Sergroum]

It's odd, since it was just renovated.

Do you have any other sources of heat in that area? Heated floors?