DENVER GUIDE

When a Denver swamp cooler quits, or winter is coming

The box on the roof is an evaporative cooler, not a refrigerant condenser. Water runs over pads, a fan pulls dry outdoor air through them, and the house is supposed to get a stream of cooler air. In October that same box needs to be shut down before a hard freeze, or spring becomes a split pad and a cracked water line. These notes cover the checks that stay off a steep roof, the minerals Denver Water actually reports, and the Xcel Energy rebate rules that apply only when you are replacing the cooler.

By Mike Maziarz · Sources checked October 12, 2026 · How we write these guides

It is not a refrigerant air conditioner

A swamp cooler, the name people use for a direct evaporative cooler, wets a pad and blows outdoor air through it. The U.S. Department of Energy’s Building America Solution Center describes that machine as a fit for dry climates, where it adds moisture to the air instead of removing it. A refrigerant condenser in the side yard does the opposite job. If the outdoor unit has fins, a fan, and a refrigerant line, and there is no water pad, you are on the wrong page. Use the air conditioner not cooling notes.

The cooled air has to leave the house. The same Department of Energy guide says doors or windows need to be open, or a relief vent needs a path, or the cooler is pushing air into a closed box. A house with every window latched can feel like a cooler that 'quit' when the only fault is no exhaust. Crack a window on the far side of the house, the way the cooler’s own instructions describe, and see whether the air starts to move. Do not prop a window in a child’s room if that creates a fall risk. A ceiling relief vent that is stuck shut is a note for a technician, not a reason to cut a hole in the ceiling.

Because the cooler adds moisture, a clammy room in July can be the equipment working, not a refrigerant problem. The indoor humidity page is the winter-dryness story. This page is the summer machine that wets the air on purpose. If the house also has a refrigerant air conditioner, say which one you ran. Running both at once, with the windows shut for the air conditioner and open for the cooler, fights itself. Pick one mode and write which one failed.

Checks before anyone climbs

Many Denver coolers sit on the roof of a ranch house. The roof is not the first stop. With both feet on the ground, confirm the breaker, once. A second trip means it stays off. Confirm the water supply valve if you can find it in a closet or on the line you already know. In cooling season that valve is open. In the heating season it should already have been closed. A pump that you can hear from inside, and a pump that is silent, are different reports. Say which one you have.

Pads you can see without climbing are fair to look at. A pad that has collapsed, pulled out of its frame, or dried into a crust will not cool even when the fan runs. Replacing a pad is house care only when the manual you still have shows how it comes out and you can do it from a safe stance. A belt you cannot see stays unseen. Do not open the electrical compartment to 'find the capacitor.' Do not stand on a ladder in wind, on a steep pitch, or on a roof that is wet from the cooler itself. Rooftop work you are not already equipped to do is the call, not a Saturday lesson.

The fan can run and the house can still stay hot if the pump is dead, the float has stuck and the pan is empty, or the pads are scaled shut. Write whether you heard water, whether the pan you can see is dry, and whether the air at the ceiling grille is moving and whether it is cooler than the outdoor air. Those four facts are the visit. A cooler that blows warm air because the pads are dry is not a refrigerant leak, and it does not get a can of refrigerant. There is no refrigerant circuit on a straight evaporative cooler.

Pads, the pan, and Denver water

Denver Water classifies the city’s water as soft to moderately hard. The utility’s hardness page says the southern collection system is moderately hard and the northern system is somewhat soft, and that hard water is not a health limit. The same utility has also noted that the water tends to form mineral scale on plumbing. Scale on a cooler pad or in a pan is that kind of deposit. It is not a claim that every Denver tap is 'hard water' in the textbook sense. Tell the technician which part of the city the house is in only if you know it. The pad in front of you matters more than the map.

The Department of Energy guide says a bleed-off or an automatic flush, sometimes called a dump pump, is how a cooler dumps mineral-heavy water and refills. That is a built feature or a plumber-and-cooler job, not a hole you drill in the pan. If the cooler already has a purge control, say so. If pads crust up every summer, say how often you have replaced them. Do not scrape scale off a pad with a knife while the fan can start. Turn the cooler off at the thermostat and the breaker you already identified before your hands are in the box.

Standing water is its own problem. The same guide says to empty the pan when the cooler will sit idle more than a few days, because standing water can breed mosquitoes and bacteria. A cooler you shut off for a cool week in June still needs the pan emptied if you can do that from a safe stance. A smell from the grille after a restart is a reason to stop using it until the pan and pads are cleaned, not a reason to spray fragrance into the duct. If you cannot reach the pan safely, that cleaning is the service call.

Winter shutdown

Fall is the other busy season for these machines. The Department of Energy guide’s winter steps are plain: shut off the water line, drain and clean the pan, and install a winter cover so dirt does not fill the box. If the cooler is ducted, dampers that are supposed to close for heating season should close, so the house is not leaking heat up a roof opening all winter. A window cooler, the guide says, should come out and be stored so the window can shut. Do not leave a window unit in the sash and call a blanket a cover.

Water left in a supply line or a rooftop pan is what those steps are trying to remove before a freeze. This page will not name a date or a temperature at which every line breaks. It will say the shutdown belongs on a mild day, from a safe stance, before the first night you would hate to be on that roof. The seasonal maintenance page is the furnace and condenser version of the same idea. The cooler is the extra machine on houses that have one.

If the only way to reach the shutoff, the drain, or the cover is a climb you do not want to make, call. A technician who winterizes coolers can shut the water, drain the pan, and set the cover without turning it into a replacement sale. Ask them to say what they closed and what they left open. A cover strapped over a pad that is still soaking, with the water valve still on, is not a shutdown. Photograph the valve in the off position if you can see it from the ground or the closet.

A rebate is a replacement question

Xcel Energy’s Colorado residential HVAC rebate application, the document the utility posts for open programs, says only new, permanently installed evaporative coolers qualify. Portable coolers do not. A standard cooler on that application needs an industry-standard rated airflow of at least 2,500 cubic feet per minute. A premium cooler needs media saturation effectiveness of 85 percent or higher, remote thermostat control, and periodic purge water control. A multi-ducted premium tier adds duct rules, including supply ducts in living spaces. Read the current application before you treat any dollar figure on an old printout as the offer. This page will not print a rebate amount.

A repair is not that application. New pads, a pump, a belt, or a float on the cooler you already have are maintenance, not a rebate form. If the cabinet is rusted through, the blower is done, or you are deciding whether to replace the cooler with refrigerant cooling, that is a different conversation. The repair or replace page keeps the fork about the defect. Ask the company to name the failed part before they name a new box. Confirm on Xcel Energy’s own site that the model and the contractor path still qualify in the year you buy.

Do not buy a cooler from a parking-lot sale because someone quoted a rebate from memory. The application is the list. If a contractor says the rebate is automatic, ask them to show the form and the equipment line that matches this install. You send the paperwork, or they do, under the rules on the form. This site does not process it and does not promise the utility will pay.

Who Denver says may install one

Denver Community Planning and Development’s mechanical-certificate page names evaporative cooling inside the heating and ventilating scope: warm-air heating, ductwork, ventilation, and evaporative cooling, among other work. That is the city describing the certificate, not this site inventing a license class or a fee. Before a cooler is replaced, or ductwork is added, ask that office whether this address needs a permit and which certificate covers it. Aurora, Lakewood, and Arvada are not Denver’s counter. The permits page is the longer version of that question.

House care, from the do-it-yourself line, includes shutting a water valve you can reach, draining a pan you can reach safely, and setting a cover the manual shows you how to set. It does not include wiring a new pump, opening a roof jack you do not understand, or telling the city a replacement was 'just a pad.' If the job changes the equipment, the permit question comes back.

When you call for a repair rather than a shutdown, give the order: fan running or not, water present or not, windows open or not, pads new or crusted, and whether anyone has already been on the roof. Ask for a written quote before parts are ordered. A cooler that needs a pump is a different visit from a cooler that needs a new curb and a new duct. Make them say which visit this is.