We did two for 550 square feet, and they are perfect. It feels like being in the warm sun. I would say it gives you an extra 10-15 degrees - our porch ceiling is 10’ high. We recently added in flexible glass/canvas roll-up curtains from Porch Enclosure Systems. When they are down and snapped shut, these heaters will warm the entire porch to the same temp as the house during the dead of winter making it a year-round space out here in Washington, DC. We definitely needed the remotes to modulate the heat. We have a fire table, and when it’s on and the curtains are closed in the winter, we need the heaters to be at only 25% or the space is way too hot - this is when it’s freezing or below outside.
Note that in addition to the heaters, you need the remote control system to customize the temperature, which costs as much as the heating units themselves. You also need a dedicated circuit, which is an additional expense. These heaters were worth every penny!
Q