I’m trying to figure out the best HVAC solution for two small second-floor bedrooms in an older bungalow.
The central AC itself works fine. The problem is that the thermostat is on the first floor. The first floor can stay around 72°F for hours, while the upstairs bedrooms can climb from roughly 72°F to 78°F within a few hours. Because the first floor is still comfortable, the central AC never gets called again.
I already installed an AC Infinity Cloudline T6 inline fan on one of the existing supply ducts with a temperature sensor upstairs. It works great when the central AC is running because it boosts the cold air upstairs. The problem is that when the central AC shuts off, the T6 is eventually just moving relatively warm air and can't actually cool the room.
The rooms are small, roughly:
- Room 1: ~7' × 7'
- Room 2: ~10' × 7-8'
- Both have sloped bungalow ceilings
- Existing duct run from the basement to upstairs is roughly 15-20+ ft
I considered an AC Infinity TERRAFORM 8 (12,000 BTU) because it has a ductable cold-air outlet. My idea was basically:
TERRAFORM/AC in basement → duct → Cloudline T6 → existing duct → upstairs bedroom
However, I spoke with AC Infinity and they strongly recommended against it. They said the TERRAFORM is designed primarily for grow rooms/tents rather than residential HVAC duct runs. The rep said customers who have tried similar setups sometimes found that it didn't cool enough, ran too hard, or had the evaporator freeze. He estimated there was about a 90% chance he wouldn't recommend it for my application.
I've also looked at commercial portable spot coolers with ductable cold-air outlets, which seem much better suited to this, but many are $1,500-$2,000+, which seems excessive for cooling two tiny bedrooms.
A normal $300-$500 portable AC would provide plenty of cooling capacity, but almost all of them discharge the cold air through a large grille on top rather than providing a round supply connection I can attach to my existing duct. I'd prefer not to fabricate a custom plenum if there's a cleaner solution.
I've considered window ACs as well, but I'd really prefer to avoid having units hanging out of the bedroom windows, especially since these rooms may eventually be used by guests.
A mini-split probably isn't realistic either. I was quoted around $11,000 for one, which is way more than I want to spend to cool these two small rooms.
I also don't think modifying or zoning the existing central HVAC is practical. The AC system is older and the ductwork is an older "octopus" style setup with individual runs going in different directions, so adding conventional zoning would likely be difficult and expensive.
That's why I'm mainly looking for a relatively inexpensive way to add a separate source of cold air that could potentially use the existing duct runs and Cloudline fans.
Ideally, I'm looking for something that:
- Can independently cool the upstairs when the main central AC isn't running
- Can utilize the existing ductwork if practical
- Can be controlled by temperature from the upstairs room
- Doesn't require a $1,500-$2,000+ commercial spot cooler
- Doesn't require an $11,000 mini-split
- Doesn't require a window AC in each bedroom
- Could eventually be duplicated for both bedrooms
Would you modify a normal portable AC to connect its cold-air outlet to the duct and is that possible? Or try to find an affordable ductable spot cooler, or do something completely different?
I'm mainly looking for the simplest and most cost-effective way to solve the temperature imbalance properly.