Can 72 Degrees Texas technicians help me choose the right size evaporative swamp cooler?

Question

Accepted Answer

Yes. Evaporative coolers are sized by airflow rather than tonnage, and the calculation depends on the volume of the space and how many air changes per hour the application needs. Getting it wrong in either direction produces a unit that disappoints.

How Evaporative Sizing Works

Refrigerated air conditioning is sized in tons of cooling capacity. Evaporative equipment is sized in CFM — cubic feet per minute of airflow.

The basic method is to calculate the volume of the space in cubic feet, then multiply by the air changes per hour the application requires and divide to get CFM.

Air changes needed vary by use. A shop or barn with heat-generating equipment needs considerably more than a covered patio. Spaces with high ceilings, west-facing walls, or metal roofs need more still.

This is why square footage alone is not enough — a shop with a twenty-foot ceiling has more than twice the volume of one with a nine-foot ceiling at the same footprint.

What Undersizing and Oversizing Each Cost

An undersized unit simply cannot move enough air to cool the space. It runs constantly and the room stays hot, and homeowners often conclude the technology does not work when the real problem was capacity.

An oversized unit wastes water and electricity, and pushes more humidity into the space than it can shed — which in Central Texas is already the technology’s weak point. It also creates more air movement than is comfortable in an occupied space.

The Exhaust Calculation Nobody Does

This is the part that most often gets skipped, and it decides whether the installation works at all.

An evaporative cooler pushes a continuous volume of air into a building. That air has to leave, or the space pressurises and airflow collapses.

Required relief opening scales directly with the unit’s CFM. Open windows, a dedicated exhaust, or a properly sized opening — but it has to be calculated, not assumed.

A correctly sized cooler with inadequate exhaust performs like an undersized one. We calculate both together.

Water Supply and Bleed-Off

Sizing also determines water consumption, and in hard Hill Country water the bleed-off rate matters.

Evaporative cooling concentrates minerals by design — water evaporates, dissolved solids stay behind. Without adequate bleed-off, scale builds rapidly on pads, in distribution lines, and on the pump.

Setting that rate correctly depends on your actual water hardness, which we test rather than estimate. Set too low and the unit scales quickly; too high and you waste water.

Pad Type and Configuration

Rigid media pads cool more effectively and last longer than aspen pads, but cost more and require more airflow to push through them.

Unit configuration — down-discharge, side-discharge, ducted or free-blowing — affects both installation and how air distributes in the space. In a long narrow shop, one large unit at one end will leave the far end warm regardless of total CFM.

The Honest Application Question

Before sizing anything, we ask what space you are cooling.

Evaporative cooling works well in shops, barns, equipment bays, and covered outdoor areas — places with constant air exchange where the humidity it adds matters less. In Central Texas, performance falls off sharply in July and August when Gulf moisture arrives.

For conditioned living space through a full summer, refrigerated air conditioning removes humidity rather than adding it. For a shop you want usable year-round, a ductless mini split cools, dehumidifies, and heats — often the better long-term answer despite a higher purchase price.

We would rather tell you that during the sizing conversation than after you have bought something that disappoints in August.