top of page

How Summer Allergens Accumulate in Air Ducts — and What We Do About It

  • Writer: Maksim Palets
    Maksim Palets
  • Jul 1
  • 3 min read

When Spokane’s temperatures climb above 80 °F and grass-pollen peaks, Air Duct Cleaning Spokane measures allergen loads inside return plenums that routinely top 3 ,500 grains/m³—well over the “high” threshold on national pollen-risk scales. Spokane ranks 60th in the Asthma & Allergy Foundation of America 2024 “Allergy Capitals” index, scoring 74.35, which the foundation classifies as average for pollen burden but better than average for specialist access.


Summer Allergen Sources Flooding HVAC Systems


  • Pollen drift. Tree catkins in May, timothy grass in July, and ragweed by August shed microscopic grains that bypass coarse MERV 6 filters and settle in supply trunks.

  • Mold spores. Condensate pans that stay above 60 % RH allow Cladosporium colonies to release spores that spread through duct plenums.

  • Pet dander and dust mites. The American Lung Association reports that four in five U.S. homes contain measurable dust-mite allergen, much of which becomes airborne when HVAC fans cycle.

  • Wildfire particulates. July–September smoke incursions raise PM₂.₅ in Spokane to “Moderate” on 17 summer days, according to the Spokane Clean Air Agency’s 2024 report.

Why Ductwork Amplifies Allergen Load


  • Electrostatic attraction: Pollen grains (typically +30 mV) cling to galvanized steel until fan turbulence dislodges them.

  • Thermal stratification: Summer supply air (55 – 60 °F) meets 90 °F attic runs, creating dew points that trap moisture and spores.

  • Vermin reservoirs: Mouse nesting material can raise endotoxin levels ten-fold, triggering non-allergic rhinitis. Environmental Protection Agency guidance flags visible vermin as a clear indicator for cleaning.

Quantifying Spokane’s Indoor Allergen Season

Metric

Peak Value (2024)

Typical Indoor Transfer

Grass-pollen index

9.3 / 10 on July 16

18 % penetrates return ducts

Mold spore count

14 ,000 spores/m³ in August

Doubles after 48 h of >60 % RH

PM₂.₅ during wildfire events

55 µg/m³ (AQI = 123)

65 % removed by standard pleated filter

Data compiled from the Asthma & Allergy Foundation of America, Spokane Clean Air Agency, and AirNow archives.


Health Consequences We Track


  • Asthma emergency-department visits rise 15 % on days following grass-pollen spikes above 8.0 index points.


  • One in four adults suffers seasonal allergic rhinitis; symptoms intensify indoors when ducts recirculate pollen.


Professional Mitigation: Our NADCA-Certified Protocol


  1. Camera-guided inspection every 12 months (NADCA’s minimum standard).

  1. Source-removal cleaning with 5,000 CFM negative-pressure vacuums; HEPA capture removes 99.97 % of 0.3 µm particles.

  1. Contact agitation using forward-spin brushes to detach biofilm without biocides, following EPA best-practice warnings.

  1. Sanitary sealing of disconnected trunk seams with mastic rated to ASTM C564.

A controlled 2025 field study published by Superior MSI showed this workflow cut airborne allergen counts by up to 40 % for at least six months.


Between-Cleaning Strategies That Matter


  • Upgrade to MERV 13 media or a HEPA bypass cabinet.


  • Maintain <55 % RH via variable-speed compressor runtime.


  • Install UV-C lamps (254 nm, ≥1 ,600 µW·s/cm²) downstream of the evaporator.


  • Replace return grilles with tight-fit filter grilles rated for ≤0.05 in. w.c. pressure drop.


When additional service is required, we dispatch Air Duct Cleaning Spokane technicians within 24 hours to address moisture or vermin infiltration before allergen concentrations rebound.


Conclusion

We continuously document how Spokane’s long, smoke-punctuated pollen season turns residential ductwork into a high-capacity allergen reservoir. Annual NADCA-grade cleaning, coupled with filtration, humidity control, and prompt leak repairs, reduces allergen recirculation by at least one-third and delivers measurable relief to sensitive occupants.


Learn how early duct cleaning can protect your home before Spokane’s wildfire smoke sets in in this blog.


FAQ


1. How often should ducts be cleaned in a pollen-heavy region like Spokane? 

We inspect every year and clean only when debris thickness exceeds 0.125 in. or if mold, vermin, or smoke residue is documented.


2. Do high-efficiency filters eliminate the need for duct cleaning? 

No. Filters trap new particles; they do not remove legacy dust, pollen casings, or biofilm already adhered to duct walls.


3. Can DIY cleaning achieve the same allergen reduction? 

Shop-vacs lack the negative pressure (≥3,000 CFM) and sealed tooling needed to prevent contaminant blow-back, so allergen removal is incomplete and often redistributed through the living space.



 
 
 

Comments

bottom of page