Yeah when I went on my honeymoon in Cal. we went up the coast for two weeks some days were hot but nights were cold, and it change considerablly ever 50 to 75 miles. So it would depend on you location. I would put heaters in and that would eliminate that concern all together. with the thermistate in them they would turn on when the temp dropped to low...... Maybe look at inline heaters, the Hydro Inline I been using for 3 years now and never had any problems with them. they would circulate the heat water thur the filter returns.