Humidity, and why bigger is worse in Spring Hill
1956 cooling degree days at 78% average humidity, so the system has to pull water out as well as cool, and one sized too large actually leaves the house damper.
1956 cooling degree days at 78% average humidity, so the system has to pull water out as well as cool, and one sized too large actually leaves the house damper
Average relative humidity around Spring Hill sits near 78 percent, which decides whether the machine's job is mostly cooling or mostly pulling water out of the air.
Why this changes what you should buy
A cooling system does two jobs: it lowers the temperature and it removes water from the air. Those two jobs compete. Removing water takes time on the coil, and a system that satisfies the thermostat quickly never gets that time. In a humid climate the comfortable house is the one whose system runs longer, not the one whose system is bigger.
Spring Hill runs about 1956 cooling degree days a year, which is a direct proxy for how many hours the compressor will actually turn - and compressors wear out by running hours, not by calendar years.
What to ask for, in order
- A Manual J load calculation, not a square-footage rule of thumb
- A system sized to that calculation, even if it is smaller than the one being replaced
- A variable-speed or two-stage compressor if the budget allows - it runs longer at lower output, which is exactly what removes moisture
- Duct inspection before sizing, because leaking ducts change the answer
Spring Hill gets roughly 57 days a year above 32 Celsius, and those are the days a system that is even slightly undersized will never catch up.
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