House heating is usually not an issue. Room temperature is most often 72F (22.2c) and aquarium temps are usually 76F-78F (24.4c - 25.5c). 26.9c (80.4F) is not harmful except higher temps do tend to increase metabolism. There is some debate as to how this affects life span, with some claims that fish in higher temperature waters are more active with shorter life spans.
Although I have sometimes seen higher temps up to 80F in summer, all of my tanks typically see 76F-78F year round so I'm no expert on prolonged higher temps.
Is your tank near a heater or heat duct outlet?
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