Where is the ideal location for a cold air return?

What are the implications/consequences of having it up high?

Should a cold air return have a filter at the inside of house location? At the furnace?

Thank you

With the cold air return at the top, hot air is drawn into the duct from near the ceiling. This is an advantage with A/C.

Normally there are filters on the low pressure side of the furnace. The vents shouldn't need them.

Labman,

This is strictly a heating application.

Where is the ideal location for a cold air return?

What are the implications/consequences of having it up high?

For heat only, I would go with the traditional floor level one. Having it high would draw off the warmest air from near the ceiling allowing the cold air to stay down where you are.

I am not a HVAC tech. A lot of this stuff I am giving the best answer I can because I don't see any better answers. Many areas I don't answer at all because others are giving good answers.

I'm w/ labman; filter at the furnace. Too many (at all return locations) may pose too much return air resistance, especially as the age.

As to placement, again I'm w/ labman; for heat, closer to the floor is better to try and pull warm air DOWN from the ceiling where it naturally collects. This helps in dispersing the air you've already paid to heat... bring it down to us.

Return airs should be high they pull in the heat that builds up in high ceilings and redistributes it threw the house in heat mode. In ac mode it pulls the heat in leaving the cold air low.