What size mini split does a 300 sq ft bedroom in Pawtucket, RI need?
300 ft² bedroom in Pawtucket, RI
6,000BTU/hr
5,929 BTU/hr of load at 19.8 BTU/ft² — the figure for 911 cooling degree days
| Head size to buy | 6,000BTU/hr |
|---|---|
| Calculated load300 ft² × 19.8 BTU/ft² | 5,929BTU/hr |
| BTU per square foot hereinterpolated from Pawtucket's 911 cooling degree days | 19.8BTU/ft² |
| What the 20 BTU/ft² rule givesthe rule overshoots by 1% here | 6,000BTU/hr |
| Summer design temperature | 89°F |
| Winter design temperaturea mini split heats too — this is the number that decides whether it can carry the room alone | 7°F |
| Summer day–night swinga moderately humid climate | 18°F |
| Days at or above 90°F | 10days/yr |
| Oversize from the size stepwithin the normal step | 1% |
Notes
- The "20 BTU per square foot" rule is a Midwest number. Pawtucket runs 911 cooling degree days, which works out to 19.8 BTU/ft² — so for this bedroom the rule overshoots by 1%. A single national figure has to be wrong somewhere, and this is where.
- Bedroom: the room where oversizing hurts most — quiet, low load, long runtimes wanted.
- 6,000 BTU/hr sits close to the load, which is where a mini split works best. Inverter equipment is happiest running long and slow at part load; it is the short, hard cycles of an oversized head that leave a room cold and damp.
- Pawtucket is moderately humid — summer nights stay within 18°F of the day's high, the signature of humid air. A meaningful share of this head's work is removing moisture, and it only removes moisture while it is running. This is the climate where an oversized head produces a room that reads cold and feels clammy.
- Do not forget the winter side. Pawtucket designs to 7°F. A cold-climate rated head will hold most of its capacity there, but a standard one will not — ask for the capacity at 7°F in writing.
- Where these numbers come from. Providence Green State Airport, 17 km from downtown Pawtucket, daily records 2015–2024. Design temperatures are calibrated against published ASHRAE values at eight airports and land within about 2°F of them.
The short answer
A 300 square foot bedroom in Pawtucket, RI needs a head of about 6,000 BTU per hour. The calculated load is 5,929 BTU/hr.
Where that number comes from
Pawtucket, RI runs 911 cooling degree days a year, which puts the room at 19.8 BTU per square foot rather than the 20 BTU/ft² the generic charts use. Applied to this room the rule gives 6,000 BTU/hr.
The winter half of the question
Pawtucket, RI designs to 7°F. A mini split is a heat pump, and its heating capacity falls as the outdoor temperature drops — the nameplate is measured at 47°F, not at the temperature you actually need it.
Sizing a single room is not sizing a house
There is no other room to absorb a mistake. An oversized head short-cycles, never runs long enough to dehumidify, and leaves the room cold and damp.
Nearby sizes
- What size mini split does a 300 sq ft bedroom in Gulfport, MS need?
- What size mini split does a 300 sq ft bedroom in Rock Hill, SC need?
- What size mini split does a 300 sq ft bedroom in Canton, OH need?
- What size mini split does a 300 sq ft bedroom in Silver Spring, MD need?
- What size mini split does a 200 sq ft bedroom in Pawtucket, RI need?
- What size mini split does a 400 sq ft bedroom in Pawtucket, RI need?
- What size mini split does a 300 sq ft living room in Pawtucket, RI need?
Read more
- Sizing a Head for a Garage or WorkshopThe standard rule of thumb assumes a room inside a house. A garage is not one, and applying it gives a number that is too small.
- The Room Over the Garage — Why It Is Always Wrong and What Fixes ItEvery house with a room over the garage has the same complaint about it, and the reasons are structural rather than mechanical.
- Where the Head Goes Matters as Much as What Size It IsA wall-mounted head throws air in one direction, and the room is conditioned in that direction.
- Ductless or Central — What Each One Is Actually Good AtThe comparison is usually framed as efficiency. The real differences are distribution, control and what the house already has.