Chest freezer seals are far better than upright freezer seals because:
* The length of the seal is smaller compared to volume,
* The height of the seal is not constrained by the closing magnets (as mechanical latches are not legal on consumer freezers),
* The temperature differential at the top of the freezer is smallest.
The specific heat capacity of air at constant pressure is ~1 kJ/kg K and 1 m^3 air has a mass of ~1.2 kg, so 1 kJ/kg K * 1.2 kg = 1.1 kJ/K. Even a freezer that exchanges 2 m^3 of air for outside air at say a 70K differential (the difference between -40C and a 30C room) for each opening only has to remove 1.1kJ/K * 2 * 70K = 154kJ, or 0.05 kWh, which is the standard unit of electricity.
An unit of residential electricity in the most expensive US State (Hawaii) is 41.2c / kWh, so opening our enormous freezer in the worst possible conditions and completely exchanging the air using the most expensive electricity costs us 2¢. It's a complete non-factor.
Source for prices: https://www.energybot.com/electricity-rates-by-state.html
closewith (https://news.ycombinator.com/item?id=32890571) is saying that:
> Chest freezers have better insulation and door seals
I'm not claiming anything either way, just pointing out that the seals are for sealing heat, not (primarily) air.
In ether case modern doors build out an insulating section around the seal, and the seal itself creates a second seal against that so it's air gapped inside the freezer as well. The seal itself of course is a hollow tube which is somewhat of an air gap with the outside too. They're pretty good, I would be surprised for their small surface area if they caused a huge conductive loss.