Hi - I see no knowledgeable MA peeps have jumped on this thread so I will take a stab at it. Here in OK, we can contact our County Assessor (or even view their website) to ask about this or see how it has been assessed. Our neighbors have a much larger house with an indoor pool. When I look at their assessment, I can compare my outdoor pool and their indoor pool, both of similar size, and see they have been listed as the same impact on the property details. However, they also have a 1900 sf "pool enclosure" listed on their report. Depending on if that area is heated or tied into the CH&A system, it can be counted as taxable square footage. Many people in smaller homes convert their garages to another bedroom, but even finished out, unless it is heated it does not count as livable square footage. Here, AC is not required.

So, I'd contact the county assessor in your area. Hope this helps!