A finished bonus room off the back of an Overland Park ranch read 84 degrees one July afternoon while the hallway thermostat downstairs held a comfortable 74. Any quote for ac installation overland park ks homeowners are gathering should start at the ductwork rather than the condenser, because a ten degree spread inside one house is almost always a delivery problem. The addition put roughly four hundred square feet of new load on a system that had handled the original house without complaint. Somebody extended the trunk line fourteen feet to reach it and left the sheet metal exactly the size it already was.
Added Square Footage Changes The Airflow Math
Cooling load is more than square footage, but square footage is where the number starts. A four hundred square foot room with two exterior walls and a west window wants somewhere near 150 cubic feet of air per minute to sit at the same temperature as the living room. Hold a meter at the register in a room like that and the reading is often 60 or 70. The equipment is making the air. It simply has no path wide enough to move it.
Duct capacity sets the ceiling on what any system delivers to a room, and no amount of tonnage in the side yard raises that ceiling. Job after job in these neighborhoods, the same thing turns up: the outdoor unit is sized correctly for the whole house, and the one branch feeding the new space is a full size too small. Homeowners are told the system is undersized. Usually it is not.
Duct Size Caps What Any System Delivers
Round duct carries a predictable amount of air at a given friction rate, and the step between diameters is steeper than most people expect. Six inch pipe moves well over twice what four inch pipe moves, which is why a fourteen foot extension in the original diameter starves a room it was never asked to serve. The branch was sized for a small bedroom. It now feeds a family room with a television, a sofa and afternoon sun.
If the addition is under about two hundred square feet and hangs off a short branch, a correctly cut takeoff and a balancing damper usually settle it. Above that, the trunk itself has to grow, and growing a trunk is fabrication work rather than an afternoon of adjustments. Attic insulation belongs in this conversation too, since half the additions we open up have thin blown coverage over the new joists and that alone moves the room a few degrees. Back to the duct, though, because the sheet metal has the final say on how much cool air ever reaches the thermostat in that room.
Sheet Metal Work Belongs In The Quote
A quote listing only a model number and a tonnage is a quote for equipment, not for comfort. Ask whether a load calculation was performed, whether static pressure was measured at the air handler, and what happens to the fourteen feet of undersized trunk. Fabricated transitions, a resized plenum and a properly cut takeoff are real line items with real labor hours behind them, and a contractor who fabricates in house can build the odd angle your framing left behind instead of forcing a stock fitting into it.
Two bids for identical tonnage can differ by thousands. Duct fabrication is usually most of that gap.
Questions Homeowners Ask About Added Load
Would a bigger air conditioner fix the hot room?
Rarely, and it often makes things worse. Oversized equipment satisfies the thermostat faster, runs shorter cycles and leaves the far end of the house with even less time to receive air. The room stays warm and the humidity climbs with it.
Can I just put a mini split in the addition instead?
Sometimes that is the honest answer, especially for a detached space or a room with no practical duct route. It is a second system to maintain, with its own filter, its own outdoor unit and its own eventual replacement. Where a resized branch can serve the room off equipment you already own, the ducted fix generally costs less over ten years.
What should a new system actually cost?
Capacity, efficiency and the amount of metal a house needs all move the number. A cost breakdown for three ton systems published in August 2026 put a standard split system swap-out between $4,200 and $9,500 installed, with heat pumps at that same capacity running $5,500 to $11,000. Duct work for an addition sits beside those ranges rather than inside them, so ask for it separately.
Size The Duct Then Size The Equipment
The best ac installation overland park ks homeowners can buy begins with a static pressure reading, a load calculation for the square footage that actually exists today, and a walk of every branch feeding the addition. Equipment selection comes after that, because the machine can only deliver what the metal allows through. Get the fourteen feet corrected while the system is apart and the bonus room stops being the room nobody sits in during August.
