How and Why to Build a Wine Cellar, Fourth Edition

Live in France here. Wine is more resilient than people give it credit for. Think about all the bottles sat on store shelves at 20 degrees for years on end. I’ve visited many a wine domain in summer and their cellars are not at 13 degrees - their cellars were built at a time when 40 degree weeks were unheard of. I recently insulated my basement cellar following the guidance in this book (https://www.amazon.com/How-Build-Wine-Cellar-Fourth/dp/1891267000/ref=mp_s_a_1_1) and I have managed to pull the max temps down by 3 degrees, however it does hold the heat in. Your idea of a vent sounds good. What is the temp difference between cellar and the outside ? How many degrees does it air out after a night of cooling ?