Phathawg is right, heat in the short term should not hurt the hard seeds, If there is any of the wind blown type seed, Heat will cause is to starts to loose viability over time. I collected seed for prairie restoration and most seed are 100% viable over a year left in the bags. The best way for long term storage is a refrigerator, that keeps it cool away from moisture, if there is moisture around seed may false sprout or mold can occur. I use an old not working refrigerator to keep it dry and the critters away. even what they do not eat, they tend to piss on the seed that causes mold and ruin the seed. I plant with in a year to 18 months, It just cost to much to feed rats, mice,& coons.