Water Conservation, Low Flow Fixtures, and Tankless Water Heaters

Low Flow Fixtures

Now days all faucet fixtures for residential plumbing are low flow devices.

While they do aid in water conservation efforts, they can be a bit inconvenient. They don’t save you water if you are filling a pot, getting a glass of water or where a measured volume of water is to be had. They can be a nuisance when you have to wait and wait for the sink to fill with water, or if you are trying to get hot water to the faucet.

Low flow fixtures cause the hot water to flow through the pipes more slowly, and so it takes longer to get your hot water. This can be especially trying when you have long pipe runs, or when your pipe is under a concrete slab and not insulated.

Slow hot water can lead to water wastage. It can take so long to get hot water at a fixture that many hot water users let the hot water run while they do something else before returning to see if it is hot yet. By the time they come back and check they are running hot water down the drain.

At this point energy is being wasted as well as water and the energy to heat the water being run down the drain is substantial… much more expensive than the water being heated.

Tankless Water Heaters

Tankless water heaters are not water conservation friendly to begin with. It takes a tankless unit longer to deliver hot water than a storage water heater since it has to heat the water first which can take 10 to 20 seconds longer than a storage water heater would deliver it.

To obtain the hot water temperature you desire you typically mix hot and cold water to get the desired temperature. This works fine with a storage water heater but can be a problem with tankless units when lower flows are used.

To turn on the tankless heater you must draw ½ to ¾ gallons per minute, depending on the water heater model you have. The outlet temperature with a tankless unit does not change as long as you don’t exceed the maximum flow, so the minimum flow of say ½ gallon per minute is at the full outlet temperature.

If you need to mix half cold and half hot to get the desired temperature you are then forced to use 1 gallon per minute which can often be a much larger flow than you need or want. This of course results in wasted water being run down the drain.

Hot Water Demand Systems

Hot water demand systems can overcome the inconvenience of slow hot water caused by low flow fixtures. Hot water demand systems pump the water to your fixture fast without running water down the drain. Your hot water is faster and you save time water and money.

A hot water demand system typically locates a small pump under the sink furthest from the water heater. When hot water is desired the user pushes the start button which activates the pump and speeds hot water to the fixture. The cooled off hot water from the last hot water use is returned to the water heater through the cold water piping so no dedicated return line is needed.

Demand systems are especially nice when used with tankless water heaters since you save both energy, with the tankless heater and water, with the demand system while having the convenience of fast hot water.

Solar with Tankless - Water Heater Guide - Water Conservation

Hot Water Recirculation System? Replace it with a Demand System!

Many residential single family and multi-family homes built in the past have full time hot water recirculation pumps and systems installed. This no doubt saves a whole lot of water, but it also wastes a tremendous amount of energy.

Hot water recirculation

Recirculating systems were typically used in larger homes, say 3,000 square feet and up. Long pipes mean long waits, and if you could afford a big house you didn’t want to have to wait forever for the hot water to arrive.

Full time recirculation systems slowly circulate the hot water through the hot water piping keeping the water in the pipes hot for instant use. Turn on a faucet and within a second or two you have hot water. It’s a great convenience, but there is a penalty to pay.

Wasting energy

Your hot water plumbing becomes a giant heat exchanger causing your water heater to fire more often and longer. Not only does this waste a huge amount of energy, but it substantially increases the wear and tear on your water heater.

Even if you heavily insulate the pipes and put the recirc pump on a clock timer, you still end up spending a lot of money for that wasted energy. It’s not helping your carbon footprint either.

Hot water demand systems

A demand hot water system on the other hand will still save you thousands of gallons of water each year, and it won’t waste any energy. Demand pumping systems typically use about $1.00 per year in electricity to run the pump. This is because the pump only runs for a few seconds and only when you really want hot water.

With a demand system, you simply push a button when you want hot water, and that starts the pump. The pump sends the water to the fixture at a faster rate than if the faucet was just run. When the hot water reaches the fixture, the pump shuts off, and when you turn on the faucet you have instant hot water. No water was run down the drain.

Installation is easy. Simply remove the old pump and replace it with the demand pump. Buttons can be hard-wired from the points of use, or wireless switches can be used.

You will still save water, and you will save energy and extend the life of your water heater. Best of all you will feel good every time you use your hot water knowing that you are doing your part to reduce global warming!

Slow Hot Water

I got this email regarding slow hot water and thought I would use it and my answer as my blog for today, so here it is.
Hello,My Dad wants to install new copper piping throughout his 2200 square-foot 2-story house. He is very concerned about 'slow hot water' and has decided he needs 1-1/2" insulation on the copper pipes instead of the standard 1/2" insulation.

He is calling around the country looking for that 1-1/2" insulation - and to Canada! He's found a plumber willing to install it for a higher price.
Do you have any studies that compare 1/2" insulation on copper pipes versus 1-1/2" insulation, and what the cost/benefits would be? And also, I think your pump solution sounds great, so could you show a comparison between your pump solution with the standard 1/2" copper pipe insulation versus no pump and 1-1/2" copper pipe insulation?

He has a regular tank water heater. Does he need to swap out his water heater?Thank you for your help,
My slow hot water answer

Typically pipe insulation is used for energy conservation purposes although adding insulation will reduce the amount of time it takes to get your hot water slightly.

The speed of the hot water is most affected by the flow rate of the fixtures and the diameter of the piping.

The speed or velocity of the water is dependent on the flow in gallons per minute and the pipe diameter. The larger diameter the pipe the slower the velocity and the longer it takes to get hot water.

Generally speaking it takes about 45 feet of ¾” inch diameter pipe to hold a gallon of water and about 70 feet for ½” diameter pipe. With a flow rate of 1 gallon per minute, the water in the ¾” pipe will flow 45 feet in about 60 seconds, and for the ½” diameter pipe the water will flow 70 feet in that same 60 seconds.

Since the flow is restricted by the fixtures, it will take longer to get hot water with the larger diameter pipes.

To get hot water to the shower fast, turn on the water in the bathtub full blast, it has the highest flow rate of any bathroom fixtures!
The second most important factor is the amount of heat that is pulled out of the piping material as the water travels to the fixture. That is where the pipe insulation comes into play.

If you had perfect pipe insulation and no heat could leak from the pipes, you would always have instant hot water. But there is no such thing as perfect insulation, and the heat will leak out fairly rapidly no matter how much insulation you use.

Pipe insulation is normally only used when a continuous hot water circulating system is being incorporated. It doesn’t really save energy, since the hot water will cool off very rapidly even with heavy amounts of pipe insulation. The reason 1-1/2” insulation is so hard to find is that it is a waste of money.

I don’t know of any studies that involve 1-1/2” thick pipe insulation.

Slow hot water delivery time is also related to the water velocity in another way. When water velocities are slow, the hot water traveling through the pipe travels much like a bullet would through the pipe.

Higher velocities cause laminar flow where a smaller diameter flow of water travels through the center of the pipe and the water in contact with the pipe walls doesn’t flow, getting the hot water to its destination even more quickly.

Plumbing layout is very important.

If you are planning on using a pumping system then the plumbing layout should be looped from fixture to fixture instead of a layout with T connections and lots of branch runs. That way a single pump can supply fast hot water to all of the fixtures.

About the water heater

I presume you mean should he replace is tank water heater with a tankless water heater? If so then the answer is no. Tankless water heaters take longer to deliver hot water since they have to turn on and start heating the water while the tank type water heater has already hot water to start the journey.

Tankless water heaters typically take 10 to 20 seconds longer to deliver hot water than tank type heaters.

So in conclusion, unless you live in a very cold area using pipe insulation will have a very small affect on how slow or fast your hot water delivery is. Increasing the pipe insulation beyond ¾” thick will most likely have no measurable effect.

Smaller pipes will deliver the hot water faster than large diameter pipes for a given flow rate.

Pumps such as the Chilipepper pump at a faster rate than typical flow rates available from the hot water fixtures.

For true "instant hot water" use a full time hot water recirculation system and insulate the pipes with at least 3/4" thick insulation.

Slow Hot Water

Today I would like to explore the topic of "Slow Hot Water".

First lets get something straight... there is no such thing as "Instant hot water" if you are referring to heating it! Even though you occasionally hear the terms "Instant water heater", when referring to tankless water heaters, technically there is no such thing. It takes time to heat water. More on that later.(maybe even my next blog actually)

Lets define what we mean by "Slow Hot Water". For our purposes slow hot water will refer to the speed at which hot water is delivered to the fixture where you are trying to obtain it, from the time you turn on the faucet.

For some of you the there is no wait... if you have a hot water recirculating pump or system for instance. A recirc pump that keeps the hot water pipe full of hot water eliminating slow hot water from your vocabulary. It's nice but expensive.

Some people will have a short wait... say less than 30 seconds, although if you are waiting for hot water 30 seconds can seem like 30 minutes, all the while running precious drinking water down the drain. Some people will have a moderate wait... say more than 30 seconds and less than 1 minute. An many have a long wait...over 1 minute. Running water down the drain for one minute will result in a waste of between 1 and 3 gallons or more, depending on the fixture flow rate.

Many of our customers have described waits of over 5 minutes! Wow. That is slow hot water!

What are the causes of slow hot water?

The first thing one thinks of is the distance from the water heater to the fixture. That can give you a rough idea, but can be very inaccurate. There are a number of reasons that the straight-line distance from your water heater to your hot water fixture is inaccurate.

Plumbing Layouts

Your actual plumbing layout plays a major role of course in the speed at which you get your hot water. The actual pipe length will depend on whether your plumbing is located in an Attic, under a crawl space, in the walls, or under a slab.

Another factor is what type of piping material is used, soft copper, hard copper, galvanized pipe, or plastic pipe? Since some of the hot water cools off from contact with the pipe as it travels to the fixture, the pipe material and weight are important variables as well in how long it takes.

Your plumbing layout quite possibly does not follow a straight line route. Most copper and galvanized pipe residential plumbing systems follow the joists and beams and make sharp right angles to get from point A to point B.

With these things in mind lets take a look at the plumbing layout for a house with the piping primarily in the crawl space. The water heater is a gas model on a stand 24" off the floor of the garage. The pipe will begin as 3/4 inch diameter hard copper pipe, and transition to smaller branch lines of 1/2 inch dia.

The pipe would exit the top of the water heater, using right angle elbows it would extend up a foot or so, and run down the side of the heater and into the crawl space below the floor. By this time you have already used 6 to 8 feet of pipe and you haven't yet started the journey to the fixture. That journey can consist of a variety of changes in direction through the use of elbows and T fittings, and the pipe diameter can be reduced to the 1/2 inch dia. for branch runs from the major hot water feed to the individual fixtures.

The diameter of the pipe is chosen to provide the minimum flow rates for the various fixtures. The flow rate is different for different types of uses. For instance, a kitchen sink fixture requires a higher flow rate than a bathroom faucet, but not as much as a bathtub fixture.

By not using a plumbing layout with a straight run from the heater to the fixture, 15 or twenty extra feet can be added to the run if it traverses several rooms. So the pipe length may very well be substantially longer than is at first apparent. Every fitting also adds to the virtual length of the pipe. (Elbows and direction changes cause a larger pressure drop than straight pipe.)

Pipe Material and Pipe Insulation and Hot Water Tunneling

As the heated water flows through the pipe, it gives up some of its heat to the pipe material. As much as 50% of the wait time is caused by the hot water being cooled off by the cold pipe as it travels through the plumbing. To make things even more interesting, the actual speed of the water through the pipe affects how much heat gets transferred. When the water is traveling at higher velocities it gives up less than the expected amount of heat because most of the HOT water is traveling through a small channel through the not-flowing cooled off hot water in the pipe.

The hot water "tunnels" through the center. With slower flows the water moves more like a bullet nosed column of hot water pushing the cooled off hot water out ahead of it. Therefore, speeding up the hot water flow rate results in a even faster than expected arrival of hot water due to the tunneling effect.

Other interesting observations are that some plastic piping such as PEX can lose more heat than copper or galvanized pipe to the ambient air space around it; another unexpected result. Insulating the pipe reduces the heat loss from the pipe and as expected this time, can reduce the wait time for that slow hot water.

Pumping the same number of gallons per minute through a smaller diameter pipe causes an increase in the velocity of the water and a shorter wait time. However, since smaller pipes have larger pressure drops, an undersized pump motor could cause an actual increase in wait time if a pumping system is being used.

Saving Water with Low Flow Fixtures or Not!

Saving water is always a priority these days, but low flow fixtures can cause a huge waste of water. Many people have fixtures with flows of down to 1 gallon per minute. With flow rates that low, the water travels in the "bullet" mode and takes longer to reach the fixture, causing more water to be run down the drain.

Electric Tankless Water Heaters (and gas)

Tankless water heaters, especially the electric tankless units, take time to heat water. They are not instant. For the water to reach full temperature it must travel completely through the heat exchanger which takes time. An Australian government study stated that tankless water heaters typically took 10 to 20 seconds longer to get hot water to the fixtures than tank type storage water heaters.

Obviously adding 10 to 20 seconds to the wait time does not help the slow hot water problem.

So there you have it, a fairly comprehensive discussion of why the hot water is slow. You know what to do about it, get a Chilipepper pump of course. A must have accessory for any water heater storage or tankless, electric or gas, or even solar, oil burner, wood burner or other heater as well! Yes, even heat pump water heaters!

Until my next blog... Bill the Hot Water Guy