What is wrong? › Commercial HVAC
Stuffy air and headaches: check outside air before anyone sells you a purifier
ASHRAE Standard 62.1 sets the minimum outdoor air for commercial and institutional buildings. A unit that has stopped bringing it in leaves CO2, odors and VOCs to build up all day.
What is probably happening
- The economizer or outside air damper is stuck closed, or was screwed shut to save energy, so the building is recirculating the same air.
- Filters overdue, or a coil growing mold, giving a musty smell when the fan starts.
- Cooking, cleaning chemicals, a new floor or paint, with no ventilation to carry it away.
- If the symptoms are dizziness, nausea or confusion, that is not stuffy air. Treat it as carbon monoxide and use the CO leaf.
Do this in the next five minutes
- Rule out CO first. If anyone is dizzy or sick, get out and call 911.
- Write down when complaints happen: mornings, after lunch, in one room, when the kitchen is busy.
- Change reachable filters and note the date.
- Ask your contractor for an outside air check against ASHRAE 62.1 for your occupancy and square footage.
- Consider a plug-in CO2 monitor for a week; rising readings through the day point at ventilation.
Do not
- Do not start with air purifiers or duct cleaning. Neither fixes missing outside air.
- Do not let the outside air damper be shut to cut bills. That is where the complaints come from.
- Do not paint or refinish floors during opening hours without extra ventilation.
Who to call
A licensed commercial HVAC contractor
Outside air dampers, economizer minimum position and filtration are all on the rooftop unit. A mold contractor comes in only if the coil or duct is visibly contaminated.
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What it should cost
$100 to $250 per hour
HVAC labor for an outside air and damper check; a CO2 or airflow measurement is usually inside the service call
Source: Angi, HVAC repair cost, updated August 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the commercial hvac page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- How much outside air is the unit bringing in now, and what does ASHRAE 62.1 call for at my occupancy?
- Is the minimum outside air damper position set, and does the actuator work?
- What filter rating does the unit take, and is a higher one possible without hurting airflow?
- Is there any moisture or growth on the coil or in the supply duct?
End the call if
- An air purifier or UV light sold before anyone measured outside air.
- Duct cleaning offered as the answer with no look at the damper.