Winter still has a strong grip on much of the country. As temperatures drop, facility managers are looking for ways they can keep their buildings at a comfortable temperature without spending lots of money on heating.
When it comes to HVLS fans, there are two schools of thought about using them in the winter: operating them in reverse to draw cold air up and spread warmer air around the room, or running them at a slower speed to recirculate heat.
Let’s examine both sides of the argument and the science behind them to see which method is best for your needs.
Reversing HVLS Fan Direction in Winter
When you think about the science behind cold and warm air, it’s easy to understand why it’s beneficial to run a fan in reverse. When air is warmed, it expands and becomes less dense than colder air, causing the warm air to rise up and “float” on the denser, colder air below it. Running a fan in reverse creates an upward draft that simultaneously pulls cold air up and forces warm air near the ceiling down into the rest of the space.
In fact, this theory is so widely accepted that in 2007, the U.S. Department of Energy passed a mandate requiring all ceiling fans manufactured in the United States to come with a reverse function. However, not everyone agrees that this is the best way to disperse heat with a fan.
Using a Gentle Breeze in the Winter
Some fan manufacturers discourage their customers from running their fans in reverse, on the basis that not only is a fan direction reversal unnecessary, it also causes uncomfortable drafts. Big Ass Fans is one such manufacturer: they conducted a study showing that running ceiling fans in reverse causes a draft.
The study concludes that a gentle forward breeze is better than reverse fan operation because it cuts down on drafts, saves energy, and still disperses heat effectively.
So which side is right? It depends on the type of space.
Why HVLS Fans in Reverse are Still Better
Big Ass Fans’ study seems to conclusively indicate that a gentle breeze is better than a full reversal during winter months. However, two key elements of their research must be noted:
- Room size. Big Ass Fans describes the place their study was conducted as a “residential lab sized to mimic a typical living space…controlled for temperature and humidity.”
- Type of fan. To conduct their research, Big Ass Fans used one of their 60-inch Haiku ceiling fan models.
This shows that the data collected in Big Ass Fans’ study skews towards residential applications, not larger commercial and industrial applications. These larger areas aren’t as susceptible to drafts, and a five-foot fan would be unable to destratify all the air in a large application.
The Bottom Line on a Gentle Breeze vs. Full Reversal
It’s true that in a residential setting, a gentle breeze may be more effective for dispersing heat without causing uncomfortable drafts, but to move heat around a space bigger than a living room– like a warehouse, distribution center or large restaurant– running your HVLS fan in reverse is undoubtedly the best option.