The video explains that dishwashers sold in 110V countries often has a hot water connection as it's too slow heating water off a 110V/10A circuit so it is more efficent to utilise the hot water pipes. However we live in NZ, a 230V country so we get dishwashers that can heat water from cold fine off a 230V/10A circuit so no need for a hot water connection.

Modern heat pump dishwashers will heat water on 110V just fine, but you are looking at 3 hour wash/dry times anyways. My Bosch isn’t connected to hot water and even has a sanitize mode.

Bosch dishwashers have something they call a “heat pump” that is a water pump that also heats the water with resistance heat. It’s not any more efficient than the normal heating coils in every other dishwasher, and it isn’t a “heat pump” that uses a refrigeration cycle (as one would use to e.g. heat their house).

Heat exchangers are used for drying, they don't have heating coils for drying.

We’re talking about heating the water, not drying. The discussion started with regards to energy used to heat water vs. using water from the hot water tap.

If you check the manual you might find that you can hook the single inlet pipe up to the hot water tap.

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.

Not just the shut off. My dishwasher's drain hose goes up into the sink's drain plumbing much higher than I would have thought.

This almost made a mess when the sink was clogged and the dishwasher tried to pump the water out but had nowhere to go.

You can install airgap for this. In usa building code mandates it on multiple states

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.

That’s exactly what it’s for. If you block the sink drain and fill it with water, you can have water flow down the dishwasher drain hose and into the sump in the dishwasher. If that happens during the rinse cycle you’re rinsing with grey water.

That is exactly why they are required in restaurants. You wouldn’t want the sewage to back up into a sink where food or dishes might be.

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

iirc its less about contaminating drinking water (there is a valve and pump to get through. rather tricky) and more about waste getting into dishwasher during cycle and you getting contaminated dishes.

my wife once decided to dump into garbage disposal a bunch of uncooked broccoli at once. it clogged garbage disposal and drain. when i tried to unclog it with plunger it backed into dishwasher (was hooked directly to garbage disposal bypassing airgap). took me hour to get everything out of dishwasher.

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.

You should actually watch the video so that you can see the graphs; it’s not pointless.

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.

I have all hot water pipes insulated in my house

And you're fully losing heat if you dump lukewarm water down the drain (instead of cycling it back to the heater) to eventually get hot water.

People who do it more or less don't care about the price of energy (except maybe in the abstract).

It's for comfort and convenience.

“16:12 The importance of purging cold water from the line”