This is exactly my thinking as I have a heat pump. Not so much of a problem in the Joburg summers with enough PV, but I am really considering a tempering valve and using that to feed the washing machine and dishwasher come winter.
My dishwasher (on ECO) uses ~1600W to heat the water twice during a cycle. With the heatpump at ~1200W when heating at the end (and I’m pretty sure more volume) I’m pretty sure it’ll help quite a bit come winter.
Yes mine uses 2kW. But for a really short period of time, so that in energy it works out maybe 1kWh of total consumption. So something like this won’t save me even one single kWh of energy 
Do these guys have another life?? vulgrim, SilverNodashi, Chris Holbson etc.
please not another skinder session about other forums/members
Maybe they are on this forum now??
He still occasionally calls me on the phone. The other guys… I have no idea
As I sent it that’s what came to mind. I went and looked at my dishwasher running when we were away. 8 minutes and then 12 minutes. Really not sure if it’s worth the effort and backpain under the cupboards.
on the topic of water/energy efficiency and/or appliance longevity
seems like on dishwashers often the short cycle is actually more economical than the “eco” setting (lower electricity consumption but at the cost of slightly more water). On my Bosch the quick programme (0.8kWh and 10L water) vs Eco (1.02kWh and 9.5L water) BUT since the quick programme only does the main wash at 45oC and rinse at 55oC it might not be adequate for the baked on cheese casserole dish and leave me having to manually dry the dishes. Also, the lower temp might have, I suspect, increased maintenance issues with soap residue build-up.
Adding “pre-heated” water might also not lead to nearly as much of a saving as one might expect on any but the newest/top-tier machines that make provision for it. Not very recent but still informative test cycle data on a Miele dishwasher (from a short report where some folks checked whether dishwashers pull a VW and adjust for testing scenarios).
The water during the machine’s “Eco” programme first sits for about 10-15 minutes before the cycle calls for water heating - i.e. there is a good chance that pre-heated water would have cooled down quite significantly and will still be reheated by the washer’s element (granted probably requiring less heating).
Unless the pre-heated source is very close to the washer and/or pipes very well insulated there is also the problem of whether any pre-heated water will reach the washer. I know most warm water outlets in my quite compact home take at least 3-4L water before warm water emerges. On a cycle with 10L TOTAL water consumption I will therefore likely only add 1-2L “preheated” water per fill.
If switching to pre-heated water - remember the inlet pipe you received with the machine is very likely only rated to 25oC.
So I guess the next big question: powder or tablets?
Edit: I have measured my dishwasher 2020 Bosch and yes, eco mode does mean less water and kWh. But the ~3 hours is too long for my family - usually because we’re rushing and somebody forgot to turn on the thing.
We often end up doing the 1 hr 65-degrees wash from batteries, which definitely irks the Optimiser in me (I’d rather do that during the middle of the day from solar, but life gets in the way).
We do powder, because it’s slightly cheaper in our experience. But you guys will probably enjoy Robert’s videos… he’s just finishing up another “No-effort November”. The videos are almost as entertaining as when your wife asks you “why are you watching a video about the popcorn button on the microwave!?”.
I love his videos! It was this video of his that made me switch to powder in the first place. My kids are well trained - they put a bit of extra powder on the door (mine is new so it doesn’t have a initial rinsing powder dispenser).
And yes, I absolutely went to check if my microwave has a popcorn button (it does) and to see if I have a bag of microwave popcorn to test it out with (I didn’t 
)
We also use powder, rinse aid and salt seperate and I would even venture to say that it wash cleaner that way.
When the dished does not wash clean, I know the salt is finished.
When the glass comes out a bit dull, I know the rinseaid needs a top up.
Loved the video on the dishwashers haha. My wife was less impressed when I started interfering with the dishwasher setup!
Tablets, but not all makes work well. Also, not long after the machine starts, you hear it drop the tablet.
Adding to that:
And//or the powder/tablets are the really cheap ones that were on special.
And/or the filters, being Bosch, needs a serious cleaning.
And/or the sprayers need a clean. Yup, you can remove them and clean them out … at least on our model.
The “water hardness” (?) is not set correctly on the machine.
It is faulty. PC board needs TLC, Eskom.
The last one, A child’s tooth, don’t ask ( she got good money for it, parents remember), was stuck inside and one day it “moved” resulting in a callout.
… every single one, jip, been there done that.
I do the same! We use this product:
If you fill the cap to just a little above the halfway line, it fills up the dispenser and leaves a little bit left that you sprinkle on the door. That makes the initial rinse a little more effective.
So did I, and ours have it too, the good kind that doesn’t ask for the size of the bag. Although I suspected it has the steam sensor thing for a while already, since it also has the Fresh Vegetables program (perfect for steaming broccoli).
We use no salt or rinse aid. Must say, I have never tried, so maybe I should, but our water should be soft enough that it isn’t necessary.
Yep. I have cycles available that are quicker and consume less power and water, but the manual tells me they are for recently used, lightly soiled dishes, or for glasses only, or for a pre-wash (which seems pointless).
Using the eco mode I can load the machine over a couple of days, even if some of the muck dries in the meantime, and run it when it’s full. On the quick mode it’s unlikely, in my household, that we’d have a full load.
So it’s horses for courses.
Another thing that the wife will NEVER allow. Has a high sense of “things need to be clean”.
I go by “let me try and see what works” - within reason. The worst outcome here will likely be having to wash the dishes again, but then I at least have a reference for the future use. 
From an ecological perspective of saving water these “eco” label machines can actually have the opposite effect because very few people RTFM, so they see “eco” and the ill-informed sales person sold them on the wonderful technology of sensors and what not, so they whack the machine into “auto” believing they are saving the planet while ending up using both more water and electricity. 
no horse in the race but he left out something important. Many tablets are very unlikely to dissolve within the first 10-15min of initial rinse with unheated water - so the advice of putting the tablet in the bottom from the start is unlikely to lead to not having “soap” by the time of the main wash. Scanning through some US patents having tablets dissolve in under 10 minutes at water temps >40oC seem the goldilocks aimed for.
Even adding normal granular detergent one might wonder how much it actually does since again initial water temperature might be too low.
I am also a 60min 65o culprit - I sometimes have some undissolved tablet granules on the door of the machine (only if packed like a hooligan might there be some residue on something on the bottom drawer). I chuck the tablet on the floor of the machine because I do not trust that slidy detergent lid to last very long.
Not dishwasher related but the other fountain of youth I employ for an appliance is to use the higher spin speeds of the washing machine very seldom. On newer machines it appears that replacing bearings will often require an entire new drum which will likely make repair uneconomical. So, I hope by keeping away from the top spinning speeds that the bearings will last longer.
The dishwasher is my domain. I know how to pack it. My wife is fine with this. She once sent me a little joke: “In every relationship there is a person who stacks the dishwasher like a Scandinavian architect and a person who stacks it like a raccoon on meth.”
My wife full well knows she is the raccoon in our relationship. 
Does anyone else pack the dishwasher absolutely full and only run it when there’s going to be domestic trouble if you don’t?
But this really cuts down on dishwasher energy usage!
