Slow Hot Water - Why Does It Take So Long?

Do you have to stand naked and shivering waiting for the slow hot water to reach the shower? Why does it take so darned long to get hot water from the water heater to the fixture?

Plagued by slow hot water?  - Why does it take so long to get hot water to the fixture?

There are a number of variables involved in getting the hot water from your water heater to your fixtures.  Obviously the distance from the water heater to the fixtures is a major factor in how long it takes to get hot water. Another important factor is what kind of pipe is used in your plumbing system?  Is it galvanized iron pipe, copper pipe, copper tubing, plastic pipe or maybe some kind of plastic tubing?

Since the material that the pipe is made out of can absorb heat from the water it is important as well.  Other factors include whether or not the pipes are insulated, the ambient temperature around the piping, and the speed of the water through the pipe.

Tankless water heaters contribute to slow hot water

One last thing to consider is what type of water heater you have.  If you have a storage type water heater where there is a big tank full of hot water just waiting to fill the pipes, you will get it much faster than if you have a tankless water heater.  The tankless heater has to first heat the water, before it can send it to you, increasing how long it takes.

Pipe diameter makes a difference

A gallon of water will fill 63 feet of 1/2 inch galvanized iron pipe, 36 feet of  3/4 inch galvanized pipe, or 20 feet of  1 inch galvanized pipe.  In the case of type K copper pipe, a gallon of water will fill 88 feet of 1//2 inch pipe, and 44 feet of 3/4 inch pipe. 

This means that if you run your faucet at 2 gallons per minute, and you have 1 inch galvanized pipe, the water will travel 41 feet per minute.  However, if you have 1/2 inch type K copper pipe, the water will travel 176 feet per minute, quite a difference.  So the smaller the diameter of the pipe, the faster the hot water will reach the fixture, given the same flow rate. 

The piping material contributes to slow hot water delivery

Since galvanized pipe has a much thicker wall than the copper pipe and is much heavier, it will absorb more heat energy from the hot water as the water flows through it. So if you have galvanized pipe it will take longer for you to get hot water than if you had copper pipe of the same length. 

Seasonal variations - ambient air temperature plays a role

In the winter it will take longer than in the summer, since the ambient temperature will be lower.  The colder the ambient temperature the more heat the pipe will suck out of the water and so the longer it will take.  Insulating the pipes does help a little.

Fixture flow rate is a big factor in the speed of the water through the pipes

 In the old days you could get shower heads that would permit flows of over 7 gallons per minute... but now days everything is low flow.  Most showers now are limited to 2 gallons per minute and many faucets are below 1 gallon per minute.  This adds significantly to the time it takes to get hot water.

Instant hot water systems use a pump to speed up the water

There are ways to speed up the delivery of hot water to your fixtures.  Use a pump.  A number of manufacturers offer various types of hot water pumping systems designed to provide speedy hot water to your fixtures. 

The oldest style system just uses a pump to circulate hot water in a loop, through the hot water piping and back to the water heater.  With that type of system you have nearly instant hot water.  However, the circulating hot water loses a lot of heat energy so it's expensive to run.  Another problem is that usually running a pipe from the last fixture back to the water heater is very expensive.

Hot water demand system

Another option is a demand type hot water system.  With a demand type system the cold water piping is used as the return line back to the water heater.  When you want hot water you "demand" it by pressing a button.  The pump turns on and circulates the water through the piping until hot water reaches the pump.  When the hot water reaches the pump it shuts off to prevent filling the cold water lines with hot water.  Now you have instant hot water when you turn on the tap or shower, and you did not wastefully run water down the drain while you waited.  With the right pump, the hot water can get to the fixture twice as fast as normal too.

If you have to wait for lengthy periods to get your hot water, then by using a hot water pumping system you will save time, water and energy.  Some such systems claim water saving of up to 10,000 gallons a year for a family of four.