Dishwashers and showers are traditionally fed by the same water heater.
The idea of running any two electricity/water-hungry appliances simultaneously is always received with skepticism.
However, in one of your multitasking escapades, you might be compelled to run a dishwasher and shower simultaneously.
But, Can You Run the Dishwasher and Shower at The Same Time?
Yes, it’s perfectly OK albeit in consideration of a few things. Running the two at the same time could help boost the efficiency of your water heater (if both your shower and dishwasher are serviced by a single water heater, that is).
Think about it – running your dishwasher and shower or any other hot water outlet at the same time means you are drawing your hot water once, not twice as you would if you ran the two outlets separately.
This way, the heater will only cycle once to fill with hot water, helping cut your utility costs.
Note that this doesn’t apply to on-demand or tankless water heaters (more on them later)
Some showers are designed to receive cold water and heat it themselves before it drizzles down your head. The same applies to some dishwashers.
If you see the Energy Star sticker on the machine, chances are it heats its own water with at least 40% energy efficiency.
Hobart AM 15 and some Frigidaire models don’t rely on your water heater. With one of these – and a shower that heats its own water – you have nothing to worry about if you are multitasking.
Dishwasher And Shower Simultaneously: Three Considerations
Let’s go back to the scenario where both your shower and dishwasher are connected to the same water heater – consider these factors:
1. Capacity & FHR of the Water Heater
Let’s assume your shower and dishwasher share the same water heater.
In this situation, unless you get the capacity right, you will run out of hot water midway.
For instance, it would be absurd to link all your hot water outlets to a 23-gallon heater in a home of 5 people.
Instead, go for the largest tank you could find for your household to keep your outlets supplied with sufficient hot water for a long time.
Here are estimates based on family size:
- 1– 2 people: 23 – 36 gal.
- 2 – 4 people: 36 – 46 gal.
- 3 – 5 people: 46 – 56 gal.
- >5 people: over 56 gal. (add 10 gal. per every extra individual)
2. Water Heater FHR Rating
Another factor to consider together with capacity is the FHR (first-hour rating) of your heater.
The FHR is basically the amount of hot water your tank can deliver in 1 hour after it has been fully heated.
If a member of your household likes to swim in the shower for hours, you must consider the FHR of your heater, or else your dishwasher might stop midway.
The FHR of your device is an indicator of efficiency (just how fast can your appliance add some degrees on your water) and can give you a hint of what your heater can sustain in the most demanding situations.
A water heater rated 90 gals. FHR will deliver 80 gallons of water in under an hour.
Start by estimating the amount of water you might need in one hour when the shower and dishwasher are running at their peak.
Use your estimation with the peak hourly usages below to figure out the right FHR for your needs:
- Showering/bathing (an individual) – 20 gal.
- Washing human hair (an individual) – 6 gal.
- Washing hands (an individual) – 2 gal.
- Dishwashing (by hand, an individual) – 6 gal.
- Shaving – 3 gal.
- Dishwasher – 14 gal.
- Washing machine – 30 gal.
3. The Water Pressure Must Be Stable
Another factor you should consider is the pressure of water in your plumbing system.
Some homes have their plumbing systems installed in such a way that drawing water from more than one point simultaneously can reduce the pressure.
If your home has such a system, then you probably shouldn’t shower and wash your dishes with the machine at the same time.
However, if your water pressure isn’t easily affected by the number of active outlets, go ahead and run your dishwasher as you shower.
Yes 100% If You Use a Tankless Water Heater
On-demand or tankless water heaters work a little differently than their regular tank counterparts.
Rather than heat your water in cycles like the traditional tank water heater, they use a set of ‘superburners’ to rapidly heat the water and avail it for immediate use.
They will deliver it directly and instantly to wherever you need it without keeping it in a tank. As you can tell, they are the most energy-efficient water heaters out there (averaging 20%).
However, the best thing about tankless water heaters in this case is that they rarely affect your household water pressure regardless of the number of hot water outlets you connect to it.
This means you can link your dishwasher and shower on it and run them simultaneously without the worry of pressure lapse.
Another great thing about this type of heater as far as multitasking is concerned is that it doesn’t heat your water in cycles.
Rather, water flows in, gets heated, and leaves to wherever it is needed all at once.
This means you don’t need to worry about the “capacity” of the “tank” (it doesn’t even have a tank: water enters and leaves immediately).
So, if you connect your dishwasher and shower on it and decide and run them at the same time, you will be guaranteed of uninterrupted hot water supply as long as you need it, even longer.
Dishwashers Don’t Use Hot Water?
Another reason why you shouldn’t worry much about running your shower and dishwasher simultaneously is that your dishwasher barely uses hot water – barely!
A lot of people don’t realize it but dishwashers don’t use hot water from the start to the end of the dishwashing process.
Instead, they only draw it at the very end of the process and during the rinse cycle.
Different manufacturers may design their appliances a little differently (consult the manual) but virtually all dishwashers operate this way.
Better yet, it’s not like the dishwasher will draw great amounts of water from your central hot water reservoir.
Too bad if you are still using old models (as you would expect, they are water-inefficient compared to modern models).
Tip: If your dishwasher is very old, say, 10 years, and you know it is inefficient – either or both water and electricity – you should always run it in tandem with your shower or any other appliance such as a washer. By maximizing the daily use of the dishwasher and other inefficient appliances you may have at home, you will save a lot of money on utility bills every year.
So, can you run the dishwasher and shower at the same time? Absolutely. It’s okay but you must consider a few factors.
Running the two at the same time means you are drawing hot water once, not twice as you would if you ran the two outlets separately.
This way, the heater will only cycle once to fill with hot water, helping cut your utility costs. Of course, the story is different if you are using tankless water heaters.