What is air stratification?
Air stratification is when warmer, less dense, air rises and collects near the ceiling while cooler, more dense, air settles at floor level. In tall spaces with minimal air movement, this creates a noticeable temperature difference between the upper and lower levels. This can be roughly estimated at 0.5 degree F per vertical foot. A stratified building is commonly overheated to keep comfortable temperatures at floor level. Reducing or eliminating overheating through destratification is a significant opportunity to reduce heating costs.
Why is stratification worse in winter?
Cold air infiltration, tall ceilings and overhead heating systems often lead to a large temperature differences between ceiling and floor. In addition, the large temperature delta between the underside of the roof deck and the outdoor air temperature promotes increased heat transfer. Without internal air mixing, the heat stays trapped overhead and heat losses can be accelerated. People feel cold below, even while the HVAC keeps running.
Do destratification fans work during heating season?
Yes, destratification fans mix ceiling air down into the occupied space. This reduces stratification and evenly balances the vertical temperature profile, reducing heating costs, and increasing comfort.
How do destratification fans reduce heating costs?
When temperatures are more even from floor to ceiling, HVAC systems don’t need to run as long to satisfy the thermostat at floor level. The reduction in ceiling level temperature slows the heat transfer through the upper portion of the walls and the ceiling. In applicable buildings, destratification can reduce HVAC costs by up to 30%.
Where should destratification fans be installed?
Destratification fans should be evenly distributed across the full space and sized appropriately to mix air from ceiling to floor. In large buildings, multiple fans work in concert to maintain consistent floor-to-ceiling temperatures as a distributed network
Common winter trouble areas include:
- warehouse floors and aisles
- manufacturing bays
- gyms and athletic courts
- retail sales floors
- cafeterias, auditoriums, and other tall school spaces
- Entrance lobbies, atriums or vestibules
Are destratification fans different from HVLS fans?
Yes. HVLS fans move large volumes of air slowly over broad areas. Great for providing an evaporative cooling effect. Destratification fans are designed specifically to correct floor-to-ceiling temperature layering in tall spaces while minimizing perceptible drafts.
Will destratification fans create drafts in winter?
No. Destratification is based on gentle, low-disruption air mixing. The goal is temperature balance and fans are often placed over circulation paths to minimize any air movement disruptions.
Can destratification reduce condensation in winter?
Yes. More consistent temperatures and better air mixing can reduce condensation issues that increase during shoulder seasons, especially around cold surfaces or temperature-sensitive areas. Destratification fans can often be used to help warm concrete slabs beyond the dew point to mitigate slip hazards. They can also be used in grocery applications to minimize condensation forming on glass display doors.
What buildings benefit most in winter?
Fifteen feet or taller, open buildings with heavy heating loads, overhead HVAC supply, and located in a cold climate including:
- warehouses & distribution
- Light industrial & manufacturing
- gyms & athletic facilities
- grocery & retail
- schools & public spaces
These spaces are most prone to winter stratification.
What to do next
If you’re seeing cold floors, comfort complaints, and heat collecting at the ceiling, destratification is a direct fix.
