[redpoint5]

My house is heated with forced air natural gas and AC cooled. Downstairs is a walkout basement with 3 bedrooms. Upstairs is the main living area and has 2 bedrooms including the master. House built in 2004.

Downstairs is always about 10 degrees cooler. In the summer, it smells a little musty. Upstairs, the AC struggles to maintain a comfortable 78 degree temperature. In the winter, downstairs will be 60 degrees when it's 70 upstairs.

My single-speed air handler draws 700 watts, so running it 24/7 is out of the question. There is one air return upstairs and one downstairs.

My thought was to block the upstairs return in the winter so hot upstairs air is forced to travel downstairs to reach the furnace, and block the downstairs return in the summer so cool downstairs air is forced to travel upstairs.

I blocked the upstairs return tonight and found the air handler is drawing 60 less watts despite having half the air intake. Air from the register is 10 degrees hotter; blowing 117 instead of 107.

I'm hoping to figure out solutions with existing equipment, but probably the recommended solution would be to have a separate HVAC system for upstairs and downstairs. If I could somehow convert the single-speed blower to variable, that would likely solve a lot of the problems since I could continuously run the blower to level out the temperature and humidity.

Replacing the entire thing has me wondering about a heat pump. AC is a 5-ton 10 SEER. Furnace is likely as inefficient as legal minimum back in the day. What is that, like 80%?