That sounds like plenty of distance. People regularly save seed in home gardens with only a few feet of separation between varieties, and there is generally only a 5-10% chance of cross pollination from insects. With that much distance it is unlikely you will have crosses. If you are saving seed and absolutely need to ensure purity, you can always get some blossom bags, and put them on your healthiest plants for saving seed.

I never thought of this! I'm doing the square foot gardening method and am growing different heirlooms and hybrids only 1 ft from each other. I hope they don't cross pollinate :/

Good FAQ here on how to prevent cross-pollination. Since tomatoes are primarily self-pollinating the crossing is minimal.

So it is only an issue if you insist on 100% seed purity. If you do then you will have to bag some of the trusses on the heirloom to prevent crossing.

Since most of us routinely grow a mix of hybrids and heirlooms we don't worry about it and save seeds anyway. That's unless trading seeds. Then purity is more important.

Dave

Here is a link that might be useful: FAQ - Preventing cross pollination