[reaperducer]

American dishwashers don't have their own heater?

Some do, some don't.

The ones that do vary in ability by overall dishwasher quality.

The ones that don't are hooked up to the kitchen's hot water line.

This is considered more energy efficient because a home's hot water heater (whether electric, gas, or another fuel) is better at heating the water in a bulk capacity than a tiny heater in the dishwasher.

The downside is that the cold water between the big water heater and the dishwasher has to be purged first for it to be really effective. If your hot water heater is in the other side of the wall, no problem. If it's six rooms away, problem.

[WheatMillington]

Hot water from the house supply isn't that hot though? My dishwasher gets MUCH hotter than the hot water supply... and I don't think the heater is "tiny" I think it's a rather substantial element. The dishwasher also doesn't need to heat up a "bulk" amount of water, just the amount of water used for washing the current load of dishes.

[reaperducer]

Hot water from the house supply isn't that hot though?

Depends on how you have it set. My current and previous hot water heaters had thermostats which permitted adjusting the temperature.

They also had warning labels on them about scalding water. If it's hot enough to scald, it's hot enough.

The dishwasher also doesn't need to heat up a "bulk" amount of water, just the amount of water used for washing the current load of dishes.

If you're washing dishes and someone is, or has recently, taken a shower; or someone is, or has recently, done laundry; or someone is, or has recently shaved or done any of the other dozen things that draw from the hot water heater, then the water is already hot and available and doesn't need to be heated all the way from cold by the dishwasher. A properly insulated hot water heater can retain heat for quite some time.

[nomel]

My cheap GE dishwasher uses a hot water line, but also has an internal heating element to "boost" it, and help dry. My electric bill definitely suffers if cold water is used.

[db48x]

Watch the video; it makes a huge difference even though the hot water input is not as hot as the water can get when the dishwasher runs its heating element.

Also the size of the heating element is irrelevant. What matters is the power dissipated. Most dishwashers in the US will use only about 900 watts of power even when plugged into a circuit that supports 1500 watts. In the EU they often hit 3000 watts. Even when just heating up a gallon or two of water that makes a huge difference.

[seanmcdirmid]

Modern dishwashers, especially in Europe, are using heat pumps as well. They don’t really benefit from the extra voltage and watts anymore.

[sgerenser]

I think you’re confused, heat pump dishwashers are extremely rare even in Europe, and basically unavailable in the U.S.

[seanmcdirmid]

That’s not true at all. Bosch is mostly heat pumps, and they are a top consumer brand in both the USA and Europe.

[sgerenser]

Bosch dishwashers are NOT heat pump dishwashers! They have a pump that also heats the water. They call it a “heat pump” but I find that terminology a bit strange, as its clearly not a heat pump (which is a term of art in appliances and HVAC). It’s just a resistive heater that is no more efficient than any other dishwasher heating element.

[tguvot]

it looks like "heat pump" in bosch dishwashers is a pump that has usual heating element inside it. https://www.bosch-home.com/us/en/product/12019637

[db48x]

Sure, but most people don’t have a modern dishwasher. It’s an appliance that lasts 20 to 30 years ergo most people have old dishwashers that were manufactured decades ago.

[seanmcdirmid]

Ya, but eventually the new tech will take over and we will be talking about very different things. Even if you just consider new builds, or hundreds of millions of Chinese buying their first dishwasher ever. Also, lots of utility districts offer incentives to upgrade to more efficient appliances.

[ninkendo]

Also, I’m way too lazy to look it up right now, but I’m quite certain I’ve heard of dishwashers that run the hot water for a little bit before letting it fill the basin. Like, I’m pretty sure this sort of thing is commonplace.

It’s not like the engineers for heaterless dishwashers are just too stupid to realize there’s an obvious workaround for having to purge the line before filling the basin. Especially when the performance is so much measurably better when you do it.

Like I said though, it’s a guess. It’s also possible efficiency certifications ding you for the excess water use.

[seanmcdirmid]

Most of the new ones (at least higher end ones?) have heat pumps that heat water and handle drying. They are efficient enough to work on 110V, and the trade off is longer cycle times. Bonus: no more plastic utensils melting because they fell to the bottom resistive heating elements.