I suspect the problem with four slice toasters is that there are only so many amps available with with a 120 volt single phase outlet. Two slice toasters can deliver more heat to the process. A four slice toaster may have to reduce heat for each slice in order not to trip the typical 15 am residential circuit breaker when all four slots are active.
However I have not undertaken to investigate and record the amp/wattage ratings for two slice vs four slice toasters. Perhaps someone can do this?
However I have not undertaken to investigate and record the amp/wattage ratings for two slice vs four slice toasters. Perhaps someone can do this?