Three years ago we remodeled and added an additional home office downstairs, during winter it is fairly cold, about 8-10 deg cooler than the 70 deg setpoint on the main living area upstairs. Most of the downstairs is somewhat cooler than upstairs, but the office is yet another half-story down and farthest from the furnace. The things aggravating the office temps are:
-shaded and north facing
-supply register is in the ceiling, long 6" flex duct run has less supply airflow than other rooms
-infinite room return, i.e. open to hallway and stairwell exacerbates stratification
-single-pane corner windows (butted glass at corner, about 15 sq ft of R-1)
-outside door primarly glass
-no downstairs return
I've done two separate experiments to simulate mini-split vs zoning modifications:
-mini-split - proxy was a portable dual-hose AC/heat-pump, vented through an access door to an adjacent vented crawl space. Heat pump is only used when office is occupied, between 1-4 hours at a time.
-zoning - proxy is I closed off all the upstairs supply registers, and am heating the entire house only from the downstairs. Carrier Infinity control says static pressures are reasonable. As the runtimes are still short this mild winter, I further have the fan recirculating on low for several additional hours.
Attached is the temp data for anyone to review, the first four days are with the "mini-split", the next four days are with the "zoning". Here's what I see:
-mini-split. The small heat pump brings the room temp up FAST. Its thermostat was inaccurate, so it was overshooting 70 deg. Once off it also cools off fairly quickly to about 68 deg, but then slowly drops overnight to 58-60 before the next morning.
-zoning. The downstairs and upstairs are now both pretty even at 70 deg, though the office is still only reaching 65-66 deg. However, this 4-5 deg difference is about half of the stratification as before, and not entirely uncomfortable. A true zoning system could bring the office to 70, but could also overheat the upstairs (e.g. Downstairs is 70, Up is 85+ )
Which permanent approach do you think is better - mini-split or zoning?