Downdraft vs Side-Draft Swamp Coolers: How to Choose the Right Mount

The choice between a downdraft and a side-draft cooler is really a choice about where the cooler lives and how its air gets into the house. Downdraft units live on the roof and drop air straight down through the ceiling. Side-draft units blow sideways, most often from a stand beside the house through a wall opening. Neither is better in general, but one is almost always better for a specific house.

The two styles use the same core parts: pads, a blower wheel, a two-speed motor, a recirculating pump, a float valve and a bleed-off line. What changes is the discharge opening, the duct path, the mounting structure and how easily you can reach the cooler to service it. For an overview of every cooler category, see types of swamp coolers.

How each style moves air into the house

Downdraft

A downdraft cooler has its discharge opening in the bottom of the cabinet. It sits on a roof curb or roof jack, and air drops through a short vertical duct (the down-duct) into either a single ceiling diffuser in a central hallway or a plenum that feeds attic ducts to several rooms. In a typical single-story ranch house, the total duct path for a central diffuser is only a few feet.

Side-draft

A side-draft cooler discharges from one side of the cabinet. Three common setups exist:

• Ground-mounted through-wall: the cooler sits on a stand and blows through a framed opening into one room or a short wall plenum.
• Ground-mounted into attic ducts: a duct rises up the outside wall, crosses into the attic and feeds ceiling registers. Ground-mounted coolers that discharge straight up into such a duct are called updraft coolers.
• Roof-mounted with an elbow: the cooler sits on the roof and a 90 degree transition turns its air down into the roof opening. This is common where an older side-draft was installed on a flat roof.

Head-to-head comparison

Airflow: why duct path matters more than discharge direction

Manufacturers commonly rate cooler airflow at zero static pressure, which means no ducts, no elbows, no grilles. Every real installation adds resistance, and the blower delivers less air as resistance rises. The details of static pressure and fan curves are in CFM explained.

A downdraft feeding one ceiling diffuser has very little resistance. A side-draft blowing straight through a wall has about the same. The difference shows up when a side-draft or updraft has to reach the attic: a riser on the outside wall, two or three elbows and a long attic trunk can add enough resistance that delivered airflow falls noticeably below the rating. Ducted installations of either style commonly deliver 10 to 30% less than the zero-static figure, depending on duct size, length and fittings.

Duct design guidance, including trunk sizing and register count, is in ductwork for evaporative coolers.

Roof issues with downdraft coolers

Roof-mounted coolers have a few problems that ground units avoid entirely:

• Leaks at the curb. The curb or roof jack must be flashed into the roof covering and sealed to the cooler's base. Technicians commonly find leaks where an old curb was reused under a new cooler with a slightly different footprint.
• Weight. A residential cooler with saturated pads and a full reservoir weighs considerably more than its shipping weight, and rigid media units are heavier than aspen units. Point loads on older roofs, especially over long rafter spans, should be checked before installing a larger unit.
• Overflow damage. A stuck float valve or a clogged overflow on a roof cooler sends water across the roof and sometimes into the duct. A properly routed overflow and bleed-off line to a drain or landscaping avoids roof damage; see water supply and drain lines.
• Service safety. Pad changes, belt adjustments and spring startup happen on the roof. On steep or tile roofs that is a real hazard, and many owners end up paying for every service call.

Practical issues with side-draft coolers

• Placement. The intake needs open air. Avoid corners where hot air pools, spots near dryer vents or trash bins, and locations where sprinklers or roof runoff hit the pads.
• Uneven distribution. A through-wall side-draft blasts air into one room. Rooms at the far end of the house cool well only if relief air is opened there, which pulls air through; see venting and relief air.
• Noise outside. The motor and blower sit at ground level next to windows and property lines. That can bother bedrooms on that side or neighbors.
• Security and access. A large framed wall opening needs a solid cover in winter and a grille that cannot be removed easily from outside.

Decision table by house type

Winter, energy and comfort differences

Both styles leave a large opening between the house and the outdoors once the season ends, and that opening is where the two styles differ in winter.

A downdraft opening is in the ceiling, where the warmest air in the house collects. Without a tight seal, heated air rises straight up the down-duct and out through the pads all winter. Most downdraft installs use a ceiling diffuser with closable louvers plus an insulated cover or a damper in the duct, and the cooler itself gets an outdoor cover. A side-draft wall opening loses less heat by stack effect because it sits lower, but it is still a big hole in an exterior wall and needs an insulated, gasketed panel.

In summer the difference flips. Cool supply air is heavier than room air, so a downdraft diffuser in the ceiling drops air that mixes down through the room, while a low side-draft opening can send a cold stream along the floor of the first room and leave the ceiling area warm. Directional grilles that throw air upward help with side-draft installs.

Replacing an existing cooler

If you already have a cooler, the cheapest path is nearly always the same discharge style and a similar footprint. The curb, duct connection, water line, bleed-off and electrical are already there, so a like-for-like swap is often a half-day job for a crew. Switching from downdraft to side-draft means closing and reroofing the old opening, framing a new wall penetration or duct path, and moving water and power. That can add more cost than the cooler itself. Typical installed costs are covered in cost to install a swamp cooler.

A replacement is also the right moment to reconsider size and media. Many older homes have aspen-pad coolers sized decades ago; moving to a rigid media unit with the same discharge style can lower supply air temperature by several degrees on the same curb. Confirm the airflow you need with the cooler size calculator and read the whole-house buying guide before ordering.