Fall Air Check
Sensors drift. Filters load.
Detectors expire.
The Fall Air Check is a twelve-point walkthrough before the building closes up for heating season. When the equipment that watches the air stops telling the truth, there's no announcement - a drifted sensor still reports a believable number, a loaded filter still passes air, and an expired gas detector still shows a green light.
“Nobody's told me anything is wrong - so we're fine, right?”
That's a reasonable assumption for most building systems. A failed pump announces itself. Air monitoring equipment doesn't. These devices don't fail to an error state - they fail to a plausible one, so the system keeps operating and keeps reporting, and nothing in the building's normal feedback loop flags a problem.
The reading looks fine
Drift produces believable numbers, not error codes.
The system still runs
Reduced airflow and rising fan energy don't trip an alarm.
The light is still green
A powered gas detector is not the same as a working one.
Three ways air equipment goes quiet
Different devices, one behavior - gradual, invisible degradation. The walkthrough is organized around the building rather than the product line, because that's how the work actually happens.
DRIFT • SENSORS
What's measuring the air?
CO2, humidity and temperature sensing that ventilation decisions depend on. Accuracy wanders over time through component aging and contamination - while the output stays plausible. Many single-channel CO2 sensors self-correct using periods of near-outdoor air, which a sealed, continuously occupied building may never provide.
LOADING • FILTERS
What's cleaning the air?
Resistance climbs as media fills, raising pressure drop, cutting airflow and driving up fan energy. This is the one degradation you can put a number on - if somebody installed the gauge. Raising filter efficiency also raises pressure drop, so an IAQ upgrade can reduce the air actually delivered.
EXPIRY • GAS DETECTION
What's watching for danger?
Sensing elements are consumable, with finite service lives and calibration intervals. Past those intervals a detector still powers up and still looks healthy. Refrigerant detection deserves particular attention this year following the industry's move to A2L refrigerants.
A better filter can mean less ventilation
Raising filter efficiency raises pressure drop. Studies of rooftop units moving from MERV 8 to MERV 13 have measured airflow falling by as much as 10%, with fan energy up roughly 11-18% - and as high as 20-30% where nobody revisits the fan afterward. Filter depth matters too: a four-inch MERV 13 generally behaves far better on airflow than a one-inch element at the same rating.
So a filtration upgrade bought to improve air quality can end up moving less air than before. Higher MERV is better only if the fan can carry it - and that's a question a filter manufacturer has no reason to raise.
The Fall Air Check
Need more information about your fall air check?
What You Can't Measure, You Can't Maintain
Your full guide to the three failure modes - how each one works, why heating season makes all three worse, and what to verify before the building seals up. Includes the twelve-point walkthrough and notes on healthcare and data center applications where verification carries documentation weight.
The Fall Air Check
Twelve things to verify before the building closes up for winter. Download a printable version that you can take to the job site and complete in a single visit.
Filters Pressure Guide
Filter loading is the one kind of air-equipment wear you can actually measure. Without a pressure gauge, filters come out too early or stay in too long, which can waste money and energy.
Where the check isn't optional
In most buildings a fall air check is good practice. In two building types it carries documentation weight - the verification record is the deliverable, not just the reassurance.
The record is the deliverable
Pressure relationships and environmental conditions in clinical spaces are governed, documented and inspected. Drifted sensing in this context isn't a comfort issue - it's a compliance finding, and "the sensor said it was fine" is not a defense.
- Space pressure relationships
- Documented environmental ranges
- Verification records that get audited
Measurement confidence is uptime
Environmental monitoring is infrastructure. Confidence in the measurement matters as much as the measurement itself, which makes drift and verification a familiar conversation rather than a novel one - and makes a scheduled fall check easier to justify than an unplanned intervention.
- Continuous environmental monitoring
- Measurement confidence and redundancy
- Change control on maintenance windows
Here's what you might be thinking about
What is a Fall Air Check?
The Fall Air Check is a twelve-point walkthrough to verify CO2 sensors, filter pressure drop, and gas detection before the building closes up for winter. Sensors drift, filters load, and detectors expire without alarming, so the check has to be scheduled.
Nothing's alarming. Why would I check?
Because none of these devices alarm when they degrade. A drifted sensor reports a plausible number, a loaded filter still passes air, and an expired detector still shows a green light. They keep reporting - just not accurately.
What if we already do preventative maintenance?
Then this is a short addition to a visit you're already making. It's a checklist, not a project - and most of it can be answered by asking whether a record exists.
What if we just replaced the filters?
Good timing. That's the moment to find out what pressure drop looks like clean, so the next change is based on a measurement instead of a calendar.
What if indoor air quality isn't a budget priority this year?
Understood. Two of the three stops are energy and code questions rather than air quality ones, and those tend to have budget behind them.
Does Alps Controls do the testing?
No. We're a controls parts distributor - we supply the sensing, filtration and detection parts, and we can tell you what to look at and where the trade-offs are. The work stays with you or your service provider.
The one source that sees the whole air path
A walkthrough spanning sensing, filtration and detection spans three product categories usually bought from three different places. In the Alps Controls online marketplace you can find all three, from a line card that offers 200+ manufacturers.
Credible on the trade-offs
A filter manufacturer has no reason to tell you a MERV upgrade might cut your airflow. A parts distributor who also supplies the pressure gauge does. Being able to name the trade-off is the difference between selling a product and advising on a system.
Many of our specialists came out of contracting - they've replaced the filter, pulled the sensor and chased the nuisance alarm, so the walkthrough is a peer conversation rather than a sales call.
Figures and intervals referenced on this page vary by manufacturer, model and application. Confirm the values that apply to the equipment actually installed. Requirements relating to refrigerant detection should be confirmed against the applicable standards and local code for the specific installation.