I feel like it's probably pointless. The dishwasher will be full of water before the hot water starts coming out the pipe. Depending on how far the dishwasher is from the water heater I guess.
In most kitchens I've seen, the dishwasher is pretty close to the sink. In fact the sink and the dishwasher often share a shut-off valve. So if you run the water at the sink until it's hot, then start the dishwasher, it will get hot water.
Problem is, that most dishwashers have a prewash and a main wash. By the time the prewash is finished and the main wash starts, the water in the supply line will have cooled off quite a bit.
Is that the point of the air gap? I can't even get a straight answer from plumbers on what it's for. I don't see how that could possibly help with a clogged drain, just seems like a secondary point for the drain water to come out.
I'm fairly sure the point of air gaps on drainage is to prevent sewerage water from backing up in to appliances if the sewerage line is blocked. It will instead spill on the floor where it will be more easily noticed and cleaned.
Pumped out water has to go somewhere . With the airgap, it will either back out your garbage disposal or pour out your airgap into the sink basin, depending on the location of the blockage.
The airgap causes the pump to be physically incapable of backfeeding the drinking water supply with dishwasher waste
Thus the video's advice (also in my dishwasher's manual) is to run the water from a nearby sink until it's hot before starting the dishwasher. Because it helps significantly to get hot water at the input when US dishwashers are limited to 1200W of heating.
When I do the dishes I hand wash those that can't be put in the dishwasher before I start the dishwasher. This ensures that the water that goes into the dishwasher is already hot.
I don't think the dishwasher will be "full of water" as it doesn't actually fill up - rather, it only uses 2 gallons maximum per cycle, about the amount that would be the bottom of basin of the washer.
That's what I meant. The water drawn from the dishwasher is small enough to not even purge the cold water from the line in many houses. So you would just be wasting heat by filling the pipe with hot water while only taking the cold water from it.
This seems like something that only makes sense when water is scarce but electricity is cheap. You’d be constantly losing heat to the poorly insulated pipes.