How Long Does It Take For A Hot Water Heater To Fill Up?

Charlie Hardcastle

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Has this ever happened to you: You’ve been enjoying a nice, warm shower when it suddenly turns cold.

This may have happened because there is no hot water in your heater, and in this case you may be wondering how long it is going to take for the water heater to fill up.

Well, that’s what we’re going to answer in this article!

How long the water heater takes to fill up again will depend on how big the tank is.

It will take about 20-30 minutes for a 40-gallon water tank to fill up. Meanwhile, an 80-gallon tank takes about 30-40 minutes to fill up. 

But how does a water heater fill up, and why may a water heater not fill up at all? We’ll attempt to answer those questions below, as well as how much energy a water heater uses. 

Troubleshooting A Water Heater: How Exactly Does A Water Heater Work?

How a water heater fills up is a fairly simple cycle. As your faucet, shower, or sink draws out hot water, the amount of water in your heater will drop.

The heater will then refill the tank with cold water automatically. 

A water heater that is taking a while to fill up, or stops filling completely may be down to a number of issues. There may be airlock, the pipes may be clogged, or there might be a leak.

But how do you tell if your water heater tank has stopped working?

There are a couple of signs, such as water has gathered around your tank, the water pressure is low, the hot water supply is limited, or the tank is making a grinding or whining sound. 

If no air comes out when the pressure valve is turned on, then the water heater is full already. There are also systems with a feature that tells you the exact water level. 

How Long Does It Take For Your Hot Water To Return To Your Heater?

So when your hot water stops, you may be wondering how long it is going to take for it to return. A few factors can affect the recovery time, such as tank size.

The bigger your water tank is, the longer you have to wait for your hot water to return. 

The first hour rating will also determine how long it takes for hot water to return. This is the amount of water that your water heater can turn into hot water in an hour. The lower the rating, the longer it takes to heat water. 

The difference in temperature can also be a factor. When we talk about the difference in temperature, we’re talking about the difference between the water that has recently entered the heater and the ideal temperature for you.

The smaller the temperature difference, the sooner the hot water will return.

What type of heater you have also plays a part, as different versions of heaters are powered by different fuel, and this can affect the time it takes for hot water to return.

For example, gas water heaters use a gas burner found at the bottom of the tank. Gas is more efficient because it heats up quicker and has the quickest recovery time. 

Electric water heaters, meanwhile, take twice as long as a gas heater to warm water up.

There is an upside to this however, as it consumes less energy, and when the water temperature decreases, the thermostat simply ignites the heating system.

Tankless water heaters cut out waiting time completely, as they provide limitless hot water instantly, making it the most advantageous option.

However, it is powered by electricity, which can be a problem if there is a power cut as you will be without hot water.

Heat pump water heaters are an upgrade to electric heaters. Although they are an improvement, they actually have a longer recovery time.

How Long Does It Take For A Hot Water Heater To Fill Up?

To reduce the recovery time by an hour to 80 minutes, you have to set them to the advanced setting, which can make your electricity bills more expensive.

Meanwhile, solar water heaters are one of the most modern forms of water heaters. They are more cost-effective, but the recovery time is still longer. A 40-gallon tank can fill up about an hour.

But if you live in a place that doesn’t get much sunlight this will not be an efficient option because it needs sunlight to create heat.

What Do You Do If Your Warm Water Doesn’t Stay Warm For That Long?

Mostly, this is due to an issue with the dip tube. The dip tube is a plastic inlet that takes the water coming into the heater to the bottom of the tank so the water can be heated.

Corrosive elements can damage the heater, and cause the cold water and the hot water to mix. 

Warm water will go to the top of the tank, until the discharge tube draws it off so hot water can be supplied to the house.

When the dip tube is damaged, the cold water instead rises to the top, and this results in colder water. 

What Do You Do If Hot Water Runs Out Quickly?

If the hot water is running out quicker than usual, take a look at your heater. Hot water running out quickly may be caused by a few things. 

Build Up Of Minerals and Sediment

Incoming water usually has some minerals in it, such as calcium and magnesium.

These precipitate and then sink to the bottom of the tank. When these minerals build up they can deplace the water, which reduces how much water is available for you.

Sediments can build up to the point they reach 15 gallons! If you have a 40-gallon water tank, in this case, only 25 gallons of hot water will be available to you.

You can tell that there is sediment build-up if you hear a hissing noise in the pressure relief valve, or if the hot water has bits of sediment in it.

But if you place a few buckets under the drain valve until the visible particles diminish then this should fix the issue.

The Gas Valve Is Broken

If an old gas valve isn’t regularly maintained then this can cause damage. You can tell if a gas valve is broken if it has a rotten egg scent, and this is because of gas leaks, and you should contact a professional right away if you notice this.

If you try to solve this problem yourself, it could lead to an explosion.

Lower Heating Elements Are Faulty

A water heater has two heating elements, these are the lower and top. Once the cold water is in the tank, the lower heating element does a lot of the work.

Meanwhile, the top heating element primarily maintains the temperature. 

Your water temperature will noticeably decrease if the lower heating element is faulty. A short-circuited wire and a build-up of sediments are the usual culprits. 

Issue With The Thermostat

The thermostat is what ignites the water heater’s heating system following the temperature dripping. If the thermostat malfunctions, the heating system cannot produce enough heat.

If this is the case, you can turn up the temperature, but if this doesn’t work, you can clean the thermostat and reset it. 

Water Heater Needs To Be Replaced

It could just be time to replace the water heater. You can tell if you need to replace your water heater according to a few factors. 

  • The water heater is over 10 years old: The older a water heater is, the less efficient it will be. 
  • The water is discolored or rusty: The heater produces rusty water, even when the pipes are not rusting.
  • Strange noises coming from the heater: Even when there is no sediment in the water, you can hear rumbling or banging sounds.
  • The heater is leaking: Consistent leaks may be caused by cracks in the water heater (see also ‘Why A Water Heater Leaks From The Overflow Pipe‘).

How Much Energy Does A Water Heater Use?

It’s a common belief that water heaters are the biggest drain of energy, and that’s not entirely untrue.

Water heaters are responsible for 14% of your electricity usage, and this makes sense when we consider how much you use your water heater for things like taking a shower, doing laundry, washing dishes, or cooking.

The amount of energy you use will depend on the wattage of your heater, what type of heater you have, its size, temperature settings, how much water is used and even how old your heater is. 

But there is a way to save on your energy costs, such as purchasing a solar-powered heater if you live in a sunny area, or purchasing an energy-efficient heater.

If your water heater is old, an insulation jacket can help save on energy, so does covering your hot water pipes with pipe sleeves, and decreasing your temperature to 120 degrees Fahrenheit or lower.

Turning off your water heater, especially when you’re going to be away from home for a while, is also helpful.

Even if you’re not going to be using your water heater, heat will still escape when the heater is turned on, albeit a small amount. But this can still make a difference to how much energy you use.

In fact, turning off your water heater can help you save up to 10% on your energy costs! 

Final Thoughts

The amount of time it takes for a water heater to fill up will depend on a few factors, but the most notable factor is how big the tank is. 

You can tell a water heater has reached capacity when no air is released after switching the pressure valve on.

If the heater takes a while to fill up, or stops filling up completely, then the factors we mentioned earlier are probably to blame. 

There are some issues with your water heater you might be able to fix yourself, but if in doubt always contact a professional.

If you suspect a gas leak especially, do not attempt to solve the problem yourself and contact a professional right away. 

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