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Like much of the Northeast, my area (Upstate New York) has a mix of single-, one-and-a-half-, and two-story houses; ranch, Cape Cod, and Colonial are the predominant styles. In houses with partial or full second stories, a common complaint is that the upper floor is too hot, sometimes running 5 to 10°F warmer than the floor below.
The best long-term solutions for hot second floors vary from house to house. In some, fixing air leaks and missing insulation will be the top priority. Others may require increasing the delivery of cool air to the problem rooms. And, in many, it takes both building enclosure work and HVAC improvements to ensure good results.
Implementing the right solution takes time. First, existing conditions need to be evaluated, ideally with the help of a trained building analyst using a blower door, thermal imaging camera, and other diagnostic tools. Based on this analysis, we need to choose a combination of improvements that meet our budget and goals. Then, we need to select and schedule contractors. Applying for incentives and financing can further extend the process.
It may be too late to feel the benefits of a comprehensive upgrade this summer, but some low-cost and no-cost steps can improve comfort immediately. Below, I’ll outline these “first aid” measures. While not substitutes for permanent improvements, they can save energy and make hot second floors more bearable for the few weeks or months of hot weather that might remain.
Why are second floors so hot?
Several factors converge to make upper floors hotter than the rooms below:
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5 Comments
Back in the day they used to sleep in the porch on the hottest days, need an enclosed porch. When harvest season came in August the farm ladies would fire up the wood stove to make fresh bread for the harvest crew, how times have changed. We got electricity here on our farm in the 1940's, still rarely use any AC.
Doug
Ceiling fans can help with temp stratification even in unoccupied upper-floor rooms, especially if the duct system was designed for heating and has floor-mounted or low-wall registers. The mean radiant temp will be lower because the ceiling won't be as hot late into the evening provided there is some call for cooling throughout the day. I otherwise agree with not using fans in unoccupied rooms.
Interesting! I did not realize that, but it makes a lot of sense.
Air Transfer Duct Between Floors for Optimal Temperature Distribution:
In my 1.5-story home with a conditioned basement and open stair connection, I considered installing a powered air transfer duct from the cold room (partially subgrade, north-end location) to the attic bedrooms. Although the tight/small house plan made me give up on this idea, I recognize now that it would have come in handy on the wirst days by combating stratification.
Leveraging the Heat Pump Water Heater (HPWH):
Due to space constraints, I placed the HPWH in the basement instead of the attic where it would have been best performing. However, I ducted the cool, dry byproduct air to the south-facing kitchen on the floor above, which has proven effective for most of the year (approximately 9 months).
Varying return air heights::
When designing, I prioritize minimizing stratification by strategically locating return air grills. In attic rooms, I locate them high on the wall, while in lower rooms, they're placed low. My simple brain’s perspective suggests this approach creates a passive system, maintaining a desirable temperature differential between floors (a few degrees) by adjusting the return air source. I welcome feedback from engineers or experts in the field.
Real-World Results from Installing a Fan:
I renovated an apartment with a loft above and addressed the 10-degree temperature difference between the loft and living room by installing the largest fan I could between the floors. The fan's impact was significant, reducing the temperature swing to within 2 degrees. Notably, I only ever needed to run the fan on its lowest speed setting.
My belief is that a larger fan blade increases surface area, momentum, and efficiency, resulting in lower wattage per CFM moved. To maximize effectiveness, I carefully planned the fan's installation, selecting the largest fan that could fit between the roof slope and loft wall. I also used an extension rod to position the fan strategically at the choke point, optimizing its geometry to minimize effort while maximizing airflow.
In contrast, my neighbor, who had an identical apartment layout without a fan, only used their loft for 6 months of the year due to heat, highlighting the benefits of this simple yet effective solution.
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