In most of the country, HVAC mold means a condensate pan and a dirty coil. In Santa Fe you have that plus something bigger: a very large share of homes here cool with evaporative coolers, and an evaporative cooler is an appliance that deliberately adds water to the air inside your house.
That is not a design flaw. In high desert air at 10 to 20 percent humidity, adding moisture is exactly how you get cool air cheaply, and it works beautifully. The problem is that the machine, the water in it, and the moisture it delivers all interact with a house that was never set up to manage indoor humidity, because nobody in Santa Fe expects to have to.
Why swamp coolers cause mold problems here
They raise indoor humidity by design
Run a cooler through July and August and the moisture load inside the house climbs. In a well-ventilated home with windows cracked, which is how these systems are meant to run, that moisture leaves. In a house where people close everything up for the AC-like feel, or where the unit is oversized, humidity builds. It condenses on the coldest surfaces available: north walls, closet backs, tile floors, window frames.
The monsoon makes people run them harder
When monsoon humidity arrives in July, the cooler stops cooling well, because it needs dry air to work. Homeowners respond by running it longer and faster, pumping even more moisture into a house on the days when the outside air is least able to carry it away. Every August we hear the same call: the cooler is broken and the house smells. The cooler usually is not broken.
The unit itself is a standing water tank
A pan of water, a recirculating pump, saturated pads and a float valve. Shut it off in September and walk away, and that pan sits with water and organic debris in it through the fall. Open it in May and the smell that comes out of the vents is the pads. That first-run-of-the-season smell is a mold and bacteria smell.
It is usually on the roof
Which means the pan, the water line and the duct penetration are all directly above finished ceiling. See attic remediation for what that does.
It pressurizes the house
A cooler pushes air in rather than recirculating it, so the house runs at positive pressure. That air has to leave somewhere, and some of it leaves through wall and ceiling cavities. You are pushing humid air into building assemblies. In a tight modern home with an oversized unit and not enough relief, this can wet a wall cavity from the inside.
What cooler service should include
- Full drain and flush of the pan, and removal of scale and sediment.
- Pad replacement, not cleaning. Aspen and rigid media pads are consumables.
- Cleaning and disinfection of the pan, distribution tubes and pump.
- Float valve adjustment and inspection of the supply line and shutoff.
- Inspection of the roof curb, flashing and duct drop for staining and leaks.
- Checking the duct damper closes fully in winter, since an open damper vents your heat and lets outdoor moisture into the duct.
- A proper winterization: drain, blow the line, close the damper, cover the unit.
The single cheapest thing you can do: drain the cooler completely before winter instead of leaving water in the pan. A large share of the cooler-related mold in this county starts in an off-season pan.
Refrigerated air and ducted systems
More Santa Fe homes are converting to refrigerated air, and plenty of the county has always had conventional forced air and heat pumps. Those systems have the standard failure points:
- The evaporator coil and drain pan. A coil condenses water by design. A clogged condensate line backs up into the pan and then into the plenum, the platform or the ceiling below.
- Flex duct in an attic or crawl. Crushed, disconnected or poorly insulated runs sweat and collect debris. Disconnected returns in a dusty attic pull in whatever is up there.
- Fiberglass-lined plenums and duct board. Once wet, the lining is porous and does not clean well. Sometimes it has to be replaced rather than cleaned.
- Filtration. A one-inch fiberglass filter run past its life lets dust load the coil, and dust plus condensate is food plus water.
- Humidifiers. Whole-house humidifiers are common here because the air is so dry. A bypass humidifier stuck open or a leaking pad assembly wets the plenum continuously.
How duct and system cleaning is done properly
Real duct remediation is not a hose down the register. It is source removal under negative pressure: the system is put under negative pressure with a HEPA-filtered collection unit, then agitated with brushes or air whips branch by branch so debris moves toward the collection point rather than into the rooms. Registers and boots come off and get cleaned individually. The blower wheel, coil and drain pan get cleaned directly, which is where most of the biological load actually is. Porous lining with growth on it gets replaced, not sprayed.
Be skeptical of very cheap whole-house duct cleaning offers. If the price is under a couple hundred dollars for an entire system, the crew is not pulling the blower wheel or the coil, and those are the parts that matter.
Cost
A cooler clean, pad change and service call is commonly one to three hundred. A proper negative-pressure duct cleaning with coil and blower service on a typical home runs several hundred to over a thousand depending on the number of runs. Replacing contaminated duct board or flex adds materially. Repairing the ceiling under a leaking rooftop cooler is a separate job, and that is where the money goes if this gets ignored.
What happens if you wait
An HVAC system is the one mold source in a house with a distribution network attached to it. Growth in a plenum or on a coil does not stay in the plenum. It goes to every room on every cycle. That is why HVAC sources produce the pattern homeowners find most maddening: everybody in the house has symptoms, the smell is everywhere and nowhere, and there is no visible growth anywhere to point at.
Related
Inspection and testing if the smell has no obvious source. Attic remediation if the unit is roof mounted. Moisture source repair for the water line and roof curb side of it.
Not sure how bad it is? Call and find out.
Tell us what you are seeing and where. We will get a local remediation contractor out for a free on-site estimate, usually the same week. Nothing is owed for the visit.
Tap to call — 24/7(505) 578-1720A seasonal routine that prevents most of it
Two appointments a year handle nearly every cooler-related mold call we hear about in this county.
Spring, before first use. Open it, drain and scrub the pan, replace the pads rather than rinsing them, check the float valve and the supply line, look at the roof curb and flashing for staining, and run it for a few minutes with the damper open before anyone is in the house.
Fall, at shutdown. Drain the pan completely, blow out or shut off and drain the supply line so it does not freeze, close the duct damper fully so you are not venting heat and pulling outdoor moisture into the ductwork all winter, and cover the unit. Water left standing in a pan from September to May is the single most avoidable mold source on any Santa Fe roof.
Frequently asked questions
My swamp cooler smells when I turn it on in spring. Is that mold?
Usually yes, a mix of mold and bacteria on the pads and in the pan from sitting wet over winter. New pads, a full pan clean and a proper winter drain next season normally solves it.
Should I switch from a swamp cooler to refrigerated air to avoid mold?
It removes one moisture source and adds a different one, since refrigerated systems make condensate. A well-maintained cooler in a properly ventilated house is not a mold problem. A neglected one above a bedroom ceiling is.
How often should ducts be cleaned?
Not on a schedule. Clean them when there is a reason: visible growth, a water event in the system, a smell that tracks with the blower, heavy construction dust, or a rodent problem.
Do UV lights in the air handler stop mold?
A properly placed UV lamp aimed at the coil can reduce growth on the coil surface. It does nothing for growth already inside your ducts or walls and it does not fix the moisture that caused it.
Can running the cooler make an existing mold problem worse?
Yes, in two ways. It raises indoor humidity, and it pressurizes the house so indoor air is pushed into wall and ceiling cavities. If you have an active problem, shut it down until you have an answer.
My whole-house humidifier runs all winter. Is that a risk?
It can be. At Santa Fe winter temperatures, indoor humidity above roughly 35 to 40 percent will condense on cold surfaces. If you are getting window condensation, your setting is too high.