Doing it in the winter it definitely will lose some heat and you'll have a poor yield on the tanks.
Big props to you for doing it. What sort of reductions in utilities and comfort improvements have you noted since doing the air sealing?
We had a 30 year old boiler that was failing so our utilities were really high regardless. We replaced the boiler in November, 2013 (original install was November 1983) and then had the never-ending-winter. So that was expensive too!
There was a definite improvement in comfort though. The upstairs felt a lot warmer overall and the bedrooms were a lot more comfortable overall.