Does this save much energy?

By the way, I’m not concerned much about the money aspects, it’s the environmental costs. And I do wait until it is full to run it.

Yes, it saves a fair mount. The drying takes place with a heating element (not unlike the element in your electric stove or your space heater) although at a lower temperature, of course.

And firing up a heating element is energy intensive.

Whether it is worth it or not – that’s a value judgment.

link

Just basic electric knowledge says it does save quite a bit. Environmental cost greatly depends on where that power comes from. Only way to know is to learn what kind of electric generation feeds your distributor. If you are in the US it’s likely mostly from coal.

@ARE_you_kidding_me has a point about power sources.
Finding out how the grid is powered in your area can be a bear. Do a bunch of searches, and call every power company you can. Somebody might tell you. When I bought a new car last year, I went with a high MPG rated regular gasoline engine because the power grid here is all about oil, so really no positive impact if I had a hybrid or a Tesla, as most of my driving is local. But geez, I had a helluva time getting straight answers from the providers.

Good for you! I always had to chuckle a little when people would brag about the environmental impact of their chevy Volt knowing the grid here is predominately coal.

@canidmajor – where I live (Atlanta) we get our power from an EMC (membership cooperative) who buys power from a different cooperative (Oglethorpe Power).

Oglethorpe has several nuclear plants, several coal fired plants, and two or three hydro power plants. Oh, they have some sort of emergency deal with the TVA if there are supply issues.

So any given day, my electricity could come from any of those sources, and I wouldn’t have any way to know which one.

If you care about your dishes, @janbb, turning off the heat dry is a lot better for them, IMO.

A lot of the water that would just naturally drip off and run down the drain is vaporized, leaving the minerals in the water to coat your dishes.
The AC not having to fight all that steam vented into the room has to be a savings, too.

In my experience there is no advantage to the heated dryer, so the energy savings is worthwhile regardless of how much or how little.

Opening the dishwasher and letting the dishes air dry work just as well.

If the dishes are still hot, they are mostly dry in a few minutes. If the dishes are cold it takes just a little longer.

My dishwasher has a “plate warmer” setting, for when I hold formal dinner parties….

never used it

Yes, it does save energy, how much I don;t know, but heating the heating element obviously uses extra electricity.
I open the door and then shake the top rack to clear off extra water that collects on top of coffee cups, glasses with depressed bottoms etc. Then leave the door open for about 45 minutes and they should be mostly dry.

@Coloma That’s what I do too.

Are the glasses spotty?

No – but that does lead to a second question. Is a rinse agent really necessary?

I don’t use a rinse agent.

The little “packs” we use have rinse agent in them now. No need for it anymore

I didn’t even know there was such a thing as ‘heat dry’. My dishwasher doesn’t have it and I haven’t missed it. I don’t use my dishwasher very often and when I do I let things dry by opening the door. I always use rinse aid but the little bottle I have has lasted five years and looks like lasting another five. The dishwasher tablets I use say nothing about rinse aid so perhaps it is superfluous.

@flutherother Well, heat dry would be the same as a drying cycle but interesting that yours doesn’t have it at all.

I wash my dishes by hand and stack them in the dishrack. My husband says, “Let God dry them.” Very little needs an extra touch of a dishtowel when it’s time to put them away. Just about the only things I regularly dry with a cloth are crystal and silver, and I don’t use much of either.

Stacking the dishes instead of hand-drying them saves my energy.

I used to use a rinse agent, and it ran out.
I no longer use a rinse agent.
There is no discernible difference.

It’s highly possible that all these answers, both heat dry and rinse agent, are somewhat skewed by the hardness of the water.
Even with a water softener, before I got city water the only way I could get my dishes reliably clean was to wash on the high temp cycle. That’s no longer necessary.

I never use the heat dry because I put plastic and silicone in my dishwasher. I was interested in buying a Bosch or Miele possibly, because they don’t use an electric hot element for drying. Although, the truth is everything is dry except the bottom of mugs and bowls as mentioned above by other jellies. I unload the bottom rack first, because when I move the top rack it might spill water into the bottom. Sometimes after unloading the bottom, I turn over any dishes that are holding water and let them air dry another 20–30 minutes and then finish unloading.

I never used rinsing agents before, but in my last house if the rinsing agent was empty the dishwasher kept telling you. I found it annoying. I put rinsing agent in it and dialed it down to the lowest amount to be released.

I think it does impact energy savings. My electric bill is usually the lowest of my neighbors pretty much everywhere I have lived, and a significant amount. I don’t use the dryer on my dishwasher. I close off rooms in the winter if it’s reasonable. My air conditioner is kept around 76–77, but that is comfortable for me. I used to keep it 78 when I was younger.

I presume, like mine, your dishwasher vents into the house. If that is the case, in winter the energy saving is virtually nil. Every “wasted” BTU is going into your house adding moisture and replacing heat that your furnace would ordinarily provide.
In summer, when your A/C is on, it saves a lot. Every BTU that goes into the house is not only unwanted, it must be removed by your A/C unit. As a first order approximation in summer you can figure the drying cycle is using twice the rated energy, one part for the dishwasher dryer and one part for the A/C unit.
Figure in winter it is free – and your humidifier does not have to run so often.

_ Every “wasted” BTU is going into your house adding moisture and replacing heat that your furnace would ordinarily provide._

True only if the dishwasher affects the thermostat, which is unlikely.

@jaytkay The thermostat is reading the air temperature, so more hot air affects when the AC or heat clicks on.

@JLeslie is correct. The T-stat reads the temperature, period. It does not know if the heat comes from the heater or the dishwasher or the oven. When the temperature gets below the set point, the heater turn on. Any heat added by the dishwasher etc. delays when the heater kicks on.
Right now natural gas is a little cheaper than electricity and oil is a little more so the cost differences are minimal.

Any heat added by the dishwasher etc. delays when the heater kicks on.

No, only heat which reaches the thermostat and is sufficient affect its operation.

Feel free to post calculations proving your point. Don’t forget to included variables for dishwasher volume, house volume, distance between dishwasher and thermostat, relative humidity, wall insulation, and proximity of the dishwasher to outside walls radiating heat to the outside.

I don’t sense any heat coming into the room from the dishwasher – unlike an oven.

But, you don’t sense any heat coming into the room when you’re hot using heated dry, correct? @janbb
I don’t use my heated dry, either, but it stands to reason the dishwasher would have to expel the hot, moist air in order to make the dishes dry?

When you open the door after a wash, hot wet air rushes out at you. That would have to go somewhere to complete a heated dry.

So, if you took a long hot shower while baking bread with the dishwasher running a heated dry, that wouldn’t effect your thermostat, @jaytkay? Because the thermostat’s not in the kitchen or bath?

Maybe you need a new thermostat.

Heat diffuses into the wider open space. Just like when you open the fridge door, or open the house door to the outside, you worry about letting the hot air in, or the cold air in, whichever you are trying to keep out to sustain a temperature.

I didn’t know where the hot air goes during a dishwasher cycle, I had never thought about before. If I open the dishwasher right after it’s done, dry cycle or not, hot air comes rushing out. If it’s been 12 hours, no heat comes out. I don’t know if the heat just slowly escapes? I don’t think it’s vented to the outside. If it escapes into the house air it is adding heat to the room, the air, the temp moves throughout the space. Heat rises, when vents come on the air moves even more than it’s natural tendency. We walk through the house we push the air around.

When I worked in Boca Raton the building had no heater. It was freezing some mornings. Not actually freezing, but very very cold. We heated the building by doing nothing but our normal putting in the lights and employees entering the building. Their body heat, and the old fashioned light bulbs, helped to heat up the space. Then customers came in, even hotter. Then the day usually heated up a little also. Sometimes we had to run air conditioning in the building when houses in the area would have their heat on.

Everything counts.

Everything counts.

Nope.

Lighting a match adds heat to your house. It does not lower your heating bill.

@jaytkay: @LuckyGuy is an engineer so I’m sure his assessment is about as accurate as accurate can be.

10 tricks for reducing your heating bill

”2. Tap heat that’s there anyway. There are plenty of activities you do around the house that generate warmth, such as cooking a meal or taking a shower. When you shower, keep the bathroom door open so steam spreads to other rooms, and don’t turn a ventilation fan on; it will rapidly remove the warm air you’re hoping to keep around.”

Air-Drying

Select the air-dry cycle instead of the heat dry cycle for drying the dishes after the load is complete. If you don’t have this option on your dishwasher, when the load has finished washing, turn the dishwasher off and open the door a crack to let the dishes dry. This keeps available heat inside, but allows the dishes to air-dry. This saves about 15 percent of your total dishwasher’s energy use.

A 100 watt incandescent bulb produces 100 watts of heat (actually power). From an energy point of view, it puts out 100 Joules of energy every second.

What temperature rise this causes depends on a lot of factors, room size, air flow, etc.

specific heat capacity of dry air is 1.00 kJ/kgC
Density of air at 30C is 1.2 kg/m³

Take a small closed room, 4 m x 4 m x 3 m or 48 m³ with 1 100w bulb.
48 m³ x 1.2 kg/m³ = 58 kg of air

100J = 1000 J/kgC x ∆T x 58 kg
∆T = 0.0017 deg C, very small change in temp.

but this occurs every second, so in an hour, we would have a 6 degree C rise. or 11 deg F

So in a small enclosed room, one 100w bulb will cause the temp to go up 11 degrees F per hour. Actually a lot.

Add a few more bulbs and it goes up a lot more. But make the room larger or open a door, and it goes up a lot less.

Source: Yahoo answers
@LuckyGuy can double check the math

It used to be common practice to put a string of 100W bulbs around plumbing sheds and small pipe houses in freezing weather to maintain above freezing temp. Quick and dirty but works well.

@jaytkay Heat is heat. You are heating your house whether you do it electrically, burn oil, set fire to your furniture, or invite friends over. (The average person expels about 100Watt of heat).

You don’t usually notice it because you have a very efficient working heating system with a good thermostat. (Ignore set-back t-state for this discussion) . Your heating system is always trying to maintain room temperature to your set point, let’s call it 68F. If the temperature drops below the set point (say 67.5F) the heating system goes on until the temperature goes above the set point (say 68.5) and it then shuts off. You furnace kicks on and off many times per day. If you were to put an hour meter on it you would see that in 24 hours it might run a total of about 6 hours when the outside temperature is 32F. It will run about 12 hours when the temperature is near 0F. It will run 0 hours if the temperature is 68F. Can you see the trend? You can figure that number . The % on time is called the duty cycle If your furnace is on for 50% of the time that is called 50% duty cycle. If you have an electric system it might be on for 2 minutes and off for 2. An oil system might go on for 5 minutes and be off for 5 minutes. Every system has a different ideal running time – that is why most T-stats have an “Anticipator setting” usually hidden and set up by the installer)
A typical furnace has a heat output rating. Mine is 80,000 BTU per hour. If at 0 F your furnace is running at 50% duty cycle to maintain the constant 68F you can say your heat loss is equal to the heat the furnace puts out, or 12 hours x 80,000 = 960,000 BTU per day, or 40,000 BTU per hour with a temprature difference of 68F = 588 BTU/hour. / Deg F.
If there is a 10F difference between your home and the outside you can figure your heat loss will be 10F x 588 BTU/hr /def F = 5880 BTU per hour. Which coincidentally is very close to 1500 Watts, the power output of a typical plug in electric heater.
Now let’s run the experiment.
Let’s do it for a day when the temperature is about 10F colder outdoors than inside. Turn off everything and only use the electric heater. Put a timer on it so you can see how much it runs per day. It will need to run at 100% duty cycle to keep the temperature at 68F. The next day try it with the dryer running and venting into your house. The timer will indicate that your heater only ran 21 or 22 hours! In both cases your house temperature was 68 F all day . But one case the heat came from the dryer instead of from your heater.

In the winter, heat that stays in your home is never wasted. If oil heat is more expensive than electricity, leave the lights on! It is cheaper!
What wastes heat? Turning on the bathroom fan, leaving windows open, letting hot water flow down the drain, turning on outside lights, feeding your kids and then sending them outside to play… anything that releases BTU outdoors.

In warm climates you want to vent as much heat outside so your A/C unit does not have to work to cool it down.

@LuckyGuy You’re insisting that lighting a match will lower your heating bill.

It seems to be a religious question for a couple of people here. I’m done.

Physics. Lighting a match will raise the temperature in your home but you can’t measure the difference with conventional technology and it won’t lower your heating bill. Things that have some substance do count and if you’re clever you can make some simple tweaks to lower your heating costs. Dishwasher, dryer, oven and even hair dryer usage all add up enough to make some difference. You could use a simple lint filter and vent your dryer into the house instead of outside. If you’re going to run it anyway don’t waste the heat. It may be pennies but it’s usually dollars. Not very many but yeah everything does in theory count when you add up all of the smaller effects. Again, physics.

@jaytkay I can tell you exactly how much a match will lower your heating bill. One match (0.1 grams) releases about one BTU when burned to the end. One gallon of heating oil (100,000 BTU delivered) is about $2.50 per gallon now. If I burn one match my heating system, at 80,000 BTU per hour, will run about 0.045 seconds less and will save 0.0025 cents of oil.

An interesting fun fact. 20 pounds of paper has the same heat value as 1 gallon of heating oil. It is wort about 12.5 cents per pound if you burn it in an efficient stove.

@jaytkay You know I’m not religious. I believe in and use the Laws of Physics.

Please, please don’t give up. Try to run an experiment to convince yourself. Do you have an hour timer on your furnace? I do. Watching that would really convince you. For one heating season I recorded the number if minutes my furnace ran every day and the Heating Degree Days reported by the National Weather Service. I then cross plotted the data. The curve was fantastically straight and consistent. I learned exactly how much I save by closing off the back bedroom, how much the stove saves, etc.
Please try it.

I know where this is going to go. I’m an engineer also and we are a practical bunch. Sorry LuckyGuy that match won’t change the bill. We can calculate the theoretical dollar amount but we can’t measure the effect against the whole system without some serious and expensive instrumentation. it’s less than a penny theoretically speaking anyway, not enough to flip the lowest ADC bit and even register. Now if you take that match and light the drapes then we are talking. I get what you are saying though and agree the physics knows know opinion, agenda or political influence. It’s as honest as it gets and I’m a devout believer also.

@LuckyGuy OK, I won’t give up, because your calculation of heating oil/match is so nifty.

But going way back up to my original assertion, you can’t say that match’s energy is going to reach the thermostat.

As you describe, closing a door makes a measurable difference. The match is the flick of a butterfly’s wing in comparison. Maybe I lit the match near a drafty window on the opposite side of the house.

And taking the match analogy back to the dishwasher – whether its heat affects the thermostat depends on too many variables to proclaim, “the dishwasher affects the thermostat with 100% efficiency.” What if the thermostat doesn’t have a linear response? What if I run the dishwasher at night when my thermostat timer turns down the temperature several degrees.

Your plot with the Heating Degree Days is treating the house and all its contents as a single unified object, it isn’t relevant to the discussion, except to illustrate your extensive experimentation (which is nonetheless kind of fun and interesting).