I have a test for the thermal performance of a building with a defined uncertainty margin (15%). I want to use it to measure the effects of refurbishments designed to improve thermal performance, but the effect of the refurbishments can be quite small (5-50%). In order to have confidence in the effect of a particular type of refurbishment, we measure across a sample of buildings. I'd like to calculate the minimum required sample size to have a particular confidence (say 95%) in the measured effect of refurbishments for a range of anticipated improvements (e.g. increasing in 5% increments from 5%).

Do I have enough information to reliably calculate a suitable sample size? And if so, what is the process to do so?

Thanks!

Richard