System replacement

Sizing is a calculation, not an inheritance

The most common way a replacement is sized in this state is to read the model number on the old condenser, work out the tonnage, and quote the same. That inherits every error already present — and there is often an error present, because the original was frequently sized the same lazy way, or sized for a house that has since had its windows replaced, its attic insulated or a room added.

A load calculation looks at the house: floor area and volume, orientation, how much glass faces west and whether it is shaded, wall and ceiling insulation, infiltration, and how many people live there. It produces two numbers, sensible and latent — the heat you feel and the moisture you have to remove — and in Tampa Bay the latent number is the one that decides whether the house is comfortable.

Why an oversized system makes a worse house

An oversized system pulls the temperature down fast and shuts off. That sounds like winning. It is not, because dehumidification only happens while the coil is cold and wet and air is moving over it, and a system that runs in ten-minute bursts never gets there. What it delivers is a house at 74°F that feels clammy, windows that sweat, a musty smell in a closet, and a thermostat somebody keeps pushing lower to chase a comfort problem that is not temperature.

The equipment suffers too. Every start is the hardest moment in a compressor's life, and short-cycling multiplies the number of them. Oversizing buys you worse comfort, higher humidity and a shorter life, and it is the default mistake because nobody ever gets a complaint on the first hot day for having gone too big.

The ducts get measured before the equipment gets quoted

A blower is rated to move a certain amount of air against a certain resistance, and most residential equipment is built around roughly half an inch of water column of total external static pressure. We put a manometer across the air handler and read what your house actually does. A great many measure far above it, and the causes are ordinary: a single undersized return, a filter grille too small for the air being pulled through it, flex duct crushed over a truss or kinked at a boot, a run that is far too long for its diameter.

If your ducting reads high, a new system will read high behind it, and the new blower will fight the same house the old one lost to. We would rather show you that number and let you decide how to spend the money than quote equipment over the top of it. Sometimes the honest answer is that the ducts are the job and the equipment can wait a year.

Matched systems, line sets, and the details on the quote

Equipment is rated as a matched pair. A condenser matched to a different indoor coil does not deliver the performance printed on either box, and the efficiency number on the quote becomes decorative. We quote AHRI-matched combinations and put the reference on the paperwork.

The existing line set is a real decision, not a footnote. If it is the right diameter, sound under a pressure test and the system is not being changed to a different refrigerant, it can often stay after a proper flush. If the old compressor failed and put acid and debris through it, or the sizes are wrong for the new equipment, it gets replaced — and a contractor who never mentions the line set has decided for you, silently, in whichever direction is cheaper for them.

The quote also names the permit and the inspection. Equipment replacement is permitted work in this state, and a price that avoids saying so is a price that is missing something.