[QUOTE=Running with Scissors]
While that may be true in the UK, US dishwashers all take their water from the hot water pipe (I’ve installed quite a few in the past 10 years).
Actually, that’s the only advantage, as far as I can tell; in the US, heating by electricity is almost always significantly more expensive than using the home’s hot water source (assuming your water heater isn’t electric)/
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I suspected it may be UK-specific; I am sticking by it until a UK plumber drops by :).
AFAIK, most hot-water systems in the UK are “on-demand” - i.e. the gas only turns on to heat the water when hot water is required. While this can be quite efficient, in the case of filling a dishwasher this will obviously use more water, as it takes time for hot water to actually come through.
I also thought that heating water electrically was more energy-efficient than by gas, but I may well be wrong. This does not refute your point; presumably electricity in the US is significantly more expensive than gas. I don’t know the situation in the UK :).
[QUOTE=Dead Cat]
I also thought that heating water electrically was more energy-efficient than by gas, but I may well be wrong. This does not refute your point; presumably electricity in the US is significantly more expensive than gas. I don’t know the situation in the UK :).
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From the end-user’s perspective, it is - it’s almost 100% efficient. But when you take generating losses into account, gas is more efficient (at least where I live, where electricity is generated using gas-fired turbines).
[QUOTE=Dead Cat]
My understanding was that most modern dishwahers (and washing machines) are “cold fill”; that is, they only take water from the cold water supply and heat it with an electric element to the required temperature. This has some obvious advantages, one of which is eliminating the need to run any hot water beforehand.
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Mirroring what RwS said, the US dishwashers run on the “hot” line. I just replaced the faucet in my kitchen sink (cost me $25, btw!) and noticed the water line to the dishwasher runs straight into the hot pipe and has its own shut off valve.
[QUOTE=Dead Cat]
…in the case of filling a dishwasher this will obviously use more water, as it takes time for hot water to actually come through.
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The same would hold true for doing a load of dishes in the sink. You would have to wait for the hot water to arrive.
Anecdotally, when I was a kid and the family got a dishwasher we found that illness didn’t spread through the family nearly as much.
It stands to reason that dishes run through a dishwasher will be more sanitary because the water is hotter, it is kept hot rather than gradually cooling in the sink and the detergent is much harsher than standard dish detergent. Dish detergent is designed to be easy on the hands while this isn’t a factor in a dishwasher. Also, the dishes are exposed to hot water and detergent for a longer period of time than during a typical sink wash.
While the dishes may not be sterile, they are a whole lot more sanitary after coming out of the dishwasher.
[QUOTE=Rick]
The same would hold true for doing a load of dishes in the sink. You would have to wait for the hot water to arrive.
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Indeed; that was not the point I was trying to make. I was simply positing a possible explanation for UK dishwashers being designed as cold-fill and US ones hot-fill. With the on-demand hot-water system, it makes more sense to use a cold fill dishwasher.
[QUOTE=Dead Cat]
I suspected it may be UK-specific; I am sticking by it until a UK plumber drops by :).
AFAIK, most hot-water systems in the UK are “on-demand” - i.e. the gas only turns on to heat the water when hot water is required. While this can be quite efficient, in the case of filling a dishwasher this will obviously use more water, as it takes time for hot water to actually come through.
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On-demand water heaters are somewhat rare here, but are becoming more popular. However, in theory, the difference in amount of water wasted between an on-demand system and a tank (or coil)-based system should be relatively small (since on-demand systems are supposed to start heating almost instantly). The majority of cold water coming out of your hot water faucet is the water that’s been sitting in the pipes between the water heater and the fixture/appliance. Unless the house is equipped with a recirculating pump (most aren’t), it’s not really going to matter whether you have a tank or on-demand.
If I may inject a humble opinion here - I’ve always felt that dishwashers are wasteful but have never looked for hard evidence to back me up. I just feel more thrifty pre-soaking and then spending 5 minutes hand rinsing than having a major appliance humming along for 60 minutes or so. Fiddling with the positioning of each and every item within the dishwasher (so the water jets can hit everything) is a bit of an annoyance as well.
I let the dishes soak in hot soapy water for a half hour or so, and then everything easily rinses clean under cold water. I use the dishwasher racks for air drying. This method possibly does use an extra gallon or two of water compared to a dishwasher but I think I come out ahead on energy savings (by not running the DW motor for an hour).
[QUOTE=Running with Scissors]
On-demand water heaters are somewhat rare here, but are becoming more popular. However, in theory, the difference in amount of water wasted between an on-demand system and a tank (or coil)-based system should be relatively small (since on-demand systems are supposed to start heating almost instantly). The majority of cold water coming out of your hot water faucet is the water that’s been sitting in the pipes between the water heater and the fixture/appliance. Unless the house is equipped with a recirculating pump (most aren’t), it’s not really going to matter whether you have a tank or on-demand.
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True - the small difference is what I was getting at, but perhaps it is too insignificant to have much effect. In other words, given the same length of piping between a hot water tank and an on-demand boiler, more water will run through before it is up to temperature with the on-demand system, due to the time taken for the boiler to fire up and actually heat the water running through.
As you explained, cold fill would seem to waste less water whichever system is used, due the backlog of cold water in the hot water pipe.