What size water heater do I need for a dishwasher?

Quick Answer

The size of the water heater needed for a dishwasher depends on several factors, including:

– Number of cycles per day – Dishwashers typically use 3-7 gallons per cycle. If you run 1 cycle per day, a 30-40 gallon heater may be enough. For 2-3 cycles, 50-80 gallons is better.

– Tank versus tankless – Tankless heaters provide a continuous flow of hot water, while tank heaters store and heat a set amount. Tankless can support multiple uses at once.

– Number of dishes – Larger families washing more dishes per cycle may need a bigger tank or higher GPM tankless heater.

– Other hot water uses – Showers, sinks, washing machine. Total household demand must be considered.

– Efficiency – Higher efficiency heaters use less energy to heat the same amount of water.

As a general guideline:

– For 1 dishwasher cycle per day, a 30-40 gallon tank or 6-7 GPM tankless heater is a good start.

– For 2-3 dishwasher cycles daily, consider 50-80 gallon tank or 8-11 GPM tankless.

But an on-site water audit looking at specific home usage is recommended for an accurate size.

How Dishwashers Use Hot Water

Dishwashers require significant amounts of hot water to effectively clean dishes. Here are some key details on how dishwashers use hot water:

– Modern dishwashers contain electric heating elements that heat wash and rinse water to very high temperatures of 140-155°F. This heated water is what cleans the dishes.

– Most dishwashers have a connection to your hot water supply. They mix this hot water with cold household water to achieve the proper temperatures.

– Each cycle uses between 3-7 gallons of hot water on average. Some larger capacity dishwashers may use up to 10-12 gallons per cycle.

– Most of the hot water is used during the final rinse cycle. This very hot 155°F water is what sanitizes and dries the dishes.

– The wash cycle temperature is lower, around 140°F, but still requires hot water for cleaning action.

– High efficiency dishwashers use rinse water heat to pre-heat the next cycle. This reduces hot water demand slightly.

So when sizing your water heater, the key factors are the number of cycles per day and gallons per cycle of your dishwasher. This sets the daily hot water draw that must be met.

Impact of Cycles Per Day

The number of cycles your dishwasher runs daily has a major impact on hot water needs:

Cycles Per Day	Typical Hot Water Use
1 cycle	3-7 gallons
2 cycles	6-14 gallons
3 cycles	9-21 gallons

As you can see, daily demand ranges widely based on dishwasher use frequency. A dishwasher used only once per day may add only 3-7 gallons of daily demand. But a large family running their dishwasher 2-3 times per day can add 12-20+ gallons of hot water demand.

This has a major impact on the size requirements of your water heater. A single cycle household may be fine with a 30-40 gallon tank. But multiple cycles demand a larger 50-80+ gallon tank for adequate capacity.

The number of cycles also impacts tankless water heater sizing. A single cycle household may need only a 6-7 GPM heater. But 2-3 cycles will require a higher flow rate of 8-11+ GPM for adequate hot water.

Understanding your unique cycles per day is crucial when selecting the optimal water heater size.

Consider Total Household Water Use

When sizing a water heater, it’s important to look at the entire home’s hot water requirements – not just the dishwasher. Key factors to consider:

– Showers – The #1 user of hot water in most homes. Showers range from 2-8 gallons per minute on average.

– Sinks – Bathroom and kitchen sinks combined may use 5-15 gallons per day.

– Clothes washer – Many clothes washers use 10-25 gallons of hot water per load.

– Bathtubs – A standard bathtub holds 30-60 gallons of water. Most homes don’t fill daily but consider occasional use.

– Other appliances – Garbage disposals, instant hot taps, hot water cleaning uses should also be included.

To determine total daily hot water use:

1. Add up water volumes and flow rates for each appliance and fixture.

2. Factor in number of uses per day.

3. This provides your expected daily hot water demand.

Size your water heater to meet or exceed this total demand. An undersized heater will lead to periodic shortages and frustration. Better to have a heater with some extra capacity and ensure ample hot water.

Tank Water Heater Sizing

For tank water heaters, the key sizing factors are:

– Tank capacity in gallons

– Heating element wattage

– Energy factor

**Tank Capacity**

As a general rule of thumb:

– 30-40 gallon tank – 1-2 people with moderate hot water use

– 40-50 gallon – 2-3 people with moderate to heavy use

– 50+ gallon tank – Larger households with high demand

Match tank size to meet or exceed your total daily hot water usage.

**Heating Elements**

Most tank water heaters have dual heating elements that turn on as needed:

– Lower wattage (1000-1500W) heats during low demand

– Higher wattage (3000-4500W) activates for heavy use

Larger tanks over 50 gallons have higher wattage elements (4500-5500W) for quick recovery during high demand periods.

**Energy Factor**

A higher energy factor means greater efficiency and lower operating costs. Look for models rated .60 or higher.

Sample Tank Water Heater Sizes

Household	Tank Size	Gallons Used
1-2 people, moderate use	30-40 gallon	15-25/day
3 people, heavy use	50 gallon	45-60/day
4+ people, high demand	80+ gallon	65-90/day

These are just general estimates – an on-site usage analysis is best for accurate sizing.

Tankless Water Heater Sizing

For tankless water heaters, the key factors are:

– Flow rate in GPM

– Activation flow rate

– Temperature rise capacity

**Flow Rate**

Flow rate measures the maximum hot water output in gallons per minute (GPM).

Flow rate must meet or exceed the combined hot water demands. For example, if you require 3 GPM for a shower, 2 GPM for a sink, and 0.5 GPM for a dishwasher simultaneously, you need a heater sized for at least 5.5 GPM.

**Activation Flow Rate**

This is the minimum flow rate at which the heater activates and begins heating water. Activation rates vary from 0.5 GPM for small models up to 1.5 GPM for larger units.

Choose a unit where the activation rate is below your typical individual uses like a shower or sink. This ensures the heater turns on when you need it.

**Temperature Rise**

This measures how much the heater can increase incoming cold water temperature. Look for a rise of at least 80°F, up to 100°F for larger homes and demand.

Sample Tankless Sizing

Household	Flow Rate	Temperature Rise
1-2 people	6-7 GPM	80°F
3-4 people	8-10 GPM	90°F
Large household	11+ GPM	100°F

Higher flow rates allow for more hot water uses simultaneously. Larger temperature rise meets demand with cooler incoming water.

Electric vs Gas Water Heaters

Water heaters are available in electric and gas (natural gas or propane) fuel types. The fuel type can impact hot water performance.

**Electric**

– Widely available, only need an electrical hookup

– Recovery rate: medium

– Installation cost: low

**Gas**

– Requires gas line hookup

– Recovery rate: high

– Operating cost: lower than electric

– Installation cost: medium

For quick hot water recovery during high demand, gas has the advantage. But electric models work well for households with moderate usage.

Make sure to size the heater based on your fuel type. Natural gas may allow for a smaller unit compared to electric since it has faster heating.

Increase Efficiency With Insulation

Insulating your hot water lines helps reduce heat loss as water travels from the heater to fixtures. This allows more hot water to reach sinks, showers, appliances compared to uninsulated lines.

Key benefits:

– Reduces wait time for hot water

– Helps maintain temperature at fixtures

– Lowers energy usage from reduced heat loss

Use insulation rated for hot water plumbing when wrapping lines. Foam, fiberglass, or molded plastic sleeves are common options.

Also insulate vertical runs from water heater to start of pipe branches. This keeps the main trunk hot. Insulate any pipes running through unheated areas like crawl spaces or garages.

Properly sized insulation helps your water heater provide more usable hot water.

Install a Hot Water Recirculating Pump

A recirculating pump creates a loop between the water heater and fixtures. This keeps hot water moving through the pipes so it’s instantly available when you turn on a hot water tap.

Benefits:

– Eliminates wasted water waiting for hot water

– Reduces energy losses from water cooling in pipes

– Provides instant hot water at faucets

Pumps connect to the hot and cold lines near the heater. A sensor or timer activates circulation based on usage patterns. Pumps use only about 15-25 watts – similar to a single light bulb.

For maximum energy savings, use an on-demand pump with activation buttons at priority fixtures like the kitchen sink. This avoids unnecessary circulation when hot water isn’t needed.

Takeaway Points

– Size your water heater based on total daily hot water demand

– Account for all fixtures & appliances requiring hot water

– For tank heaters, choose a capacity at least 10-20% above daily use

– Tankless heaters must meet combined flow rates at peak times

– Insulate pipes and install a recirculating pump to optimize efficiency

– Perform an at-home usage analysis for accurate sizing as needed

Conclusion

Sizing a water heater for an efficient dishwasher requires looking at the entire household’s hot water requirements. Key factors are daily dishwasher cycles, capacity of tank heaters, and flow rates of tankless models.

Start by estimating total use from all fixtures and appliances needing hot water. This sets the minimum size – then add extra capacity if possible. Insulate hot water lines and install a recirculating pump to optimize the system. Accurately sizing your water heater ensures an ample supply of hot water for great dishwasher performance.