I recently added heat and air to an upstairs living area (2 bedrooms), previously there were ducts (very small) from the main system downstairs. The rooms never cooled adequately, so we always blocked off the vents and used 2 upright portable AC's. Both of the portable units were both 1 ton each. The smaller room (150 sq ft) cooled fine but the larger room (~400 sq ft) never cooled especially when the summers in Oklahoma had 50 days straight above 100 degrees. Both rooms face the south and have 3 windows each and have lots of surface area (sloped walls).
When sizing the unit the contractor did not do any calculations, but rather based his recommended size on other houses in the neighborhood and somewhat on the portable units I had been using knowing that the central air unit would be much more efficient. He suggested a 2 ton unit. I am an engineer by trade and education so I researched a lot and determined that I would ask for an upsize of 20% and go to a 2.5 ton. I knew this was not preferred based on the footage versus the tonnage.
Now, as expected the unit cools great, but the humidity hangs around the 60-70% range. I know this is due to the lack of runtime which is reducing the dehumidification process. Typical runtime is approx 10 minutes. So like many others who have posted, I am looking for ways to improve my situation and would like some advice. I understand to correctly fix the problem I should replace the unit, but that is not in the cards right now.
I believe these are my options:
• Add a dehumidifier to the system. $$$
• Use a dehumidifier in the bedrooms. $
• Slow the airflow (motor speed) (already did this with slight improvement)
• Increase the cooling load to include an uncooled/unheated sunroom and possibly the garage – not sure how to place a thermostat when cooling areas that are not connected?$
The AC contractor I used is a very reputable company and has been great to work with, so no real issues there especially since I asked for the larger unit.
Thanks in advance!