Hot water supply improvement guide:

This article explains how to improve the hot water pressure or temperature in a building.

We list and decribe detailed procedures for diagnosing and fixing the various causes of running out of hot water, hot water that is too weak in flow (bad pressure), hot water that is not hot enough (temperature too low), and other water heating problems such as water heater efficiency, noises, odors, or contamination.

Topics discussed include comparison of alternative water heating methods, costs, capacities, recovery rates, & safety; Mixing valves - anti-scald valves on heating boilers, tankless coils, & water heaters, how they work; Smart use of shower controls to save hot water heating costs; How an anti-scald valve can increase the total amount of hot water obtained from a tankless-coil hot water system.

How do we Improve the Domestic Hot Water Pressure or Temperature?

This article summarizes all of the ways you may want to improve hot water systems at a building, including hot water quantity (stop running out), hot water pressure (flow is too weak), hot water heater efficiency (stop wasting money), and other building hot water supply problems and aggravations.

We start with a description of how to get more hot water when using a tankless coil on a heating boiler to get domestic hot water for washing and bathing.

In a list of articles at this website we then provide links to detailed diagnostic procedures for each type of hot water supply issue.

Before you start fixing or buying stuff to fix a hot water problem hot water problems, you might want to check there to be sure you're fixing the right problem.

Diagnostic guides for all kinds of hot water troubles are summarized at WATER HEATER PROBLEM DIAGNOSIS.

The topics discussed in this article address improving hot water flow and improving hot water total quantity.

There are several different hot water problems - distinguishing among them tells us what sort of corrective action will be needed.

1. Poor hot water flow, or bad hot water pressure, which is usually a piping or clogging problem or an overall building water pressure problem
2. Poor hot water quantity: not enough hot water, or running out of hot water very quickly. Insufficient hot water quantity may be due to the way hot water is being made (a water heater that is too small, a tankless coil on a new small heating boiler, or an instantaneous water heater that is being asked to supply hot water too rapidly.
3. Hot water temperature that is not hot enough: water temperature is just too cool. Insufficient hot water temperature may be due simply to the setting of a temperature control on a water heater or mixing valve, or it may be due to flowing water too fast through a tankless coil. Hot water that is not hot enough can be caused by quite a list of problems, some of which are easy to correct.

How to Increase Hot Water Quantity & Flow When a Tankless Coil is Installed - how to avoid running out of hot water

A tankless coil used to produce hot water is shown in the sketch at the top of this page and again in the photograph at left. The black rectangle is the mounting plate that bolts the tankless coil to the heating boiler - in this case it happens to be a steam boiler.

On this tankless coil cold water enters at the lower of the two pipes connected to the coil. You'll also see that the cold water line continues to enter the bottom of the anti-scald valve.

The hot water leaves this tankless coil from the upper pipe connected to the coil, where it flows down to enter the mixing valve (tempering valve) at the left side of that valve (see the black temperature setting knob on top of the valve?). We discuss anti-scald valve or tempering valves in detail just below.

Tempered hot water (mixed hot and cold) leaves at the right side of the mixing valve and heads for the plumbing fixtures in the building.

On many heating boilers the tankless coil mounting plate is round, not rectangular, and it may be located on the top of the heating boiler as well as on the front, back, or either side of the heater.

Use a flow limiter to increase the length of time that you can run the hot water and to increase hot water temperature

Tankless coils do not provide infinite hot water. Cool water entering the coil draws heat out of the boiler water and into the house water.

The oil or gas burner that reheats the heating boiler cannot pump heat into the boiler as fast as the tankless coil is removing heat. That's because water is entering the coil at 40 to 55 deg F in most cases, and it's trying to leave at the boiler temperature that may be close to 200 degF.

So if you run water too fast through the tankless coil it'll draw heat out of the boiler quickly and you'll have great hot water pressure, but not for very long. Then you'll just have tepid or cold water pressure. Some tankless coils have a flow limiting valve mounted right at the coil to prevent water from flowing through the coil too fast.

Using a flow limiting valve on a tankless coil lets you run the hot water longer before you run out by forcing you to run it more slowly.

Use of a flow limiting valve, because it slows the passage of cold water through the water heater, will also permit the water to arrive at the plumbing fixture at a higher temperature - the hot water will be hotter.

Intelligent use of shower controls to restrict hot water flow can save hot water costs and provide longer shower bathing time

Even when a flow limiter is not installed in hot water piping, a bather can save on hot water heating costs by smart use of shower controls.

Some bathers turn the hot water all the way to it's fastest flow position, followed by turning on lots of cold water in order to avoid being scalded. Instead of this fastest-flow best water pressure approach, turn the hot water to a less powerful stream, which will require also turning on less cold water to obtain a comfortable shower temperature.

This method of bathing does not really provide a greater quantity of hot water in a building, but by drawing hot water out of the water heater more slowly, one can either have longer time in the shower, or subsequent bathers can have adequate hot water at less total water heating cost.

Use an anti-scald valve to increase hot water quantity and protect from hot water burns

Why does an Anti-Scald Valve, mixing valve, or tempering valve on a tankless coil hot water system increases the total amount of hot water available?

The use of a mixing valve or anti-scald valve at a tankless coil permits us to set the Honeywell 6006 limit control switch or other boiler temperature or water heater temperature limit control to a higher number without having to worry about scalding occupants of the building.

Keeping the water at a higher temperature inside the heating boiler (with a tankless coil system) or in the water heater (with a separate domestic water heater or indirect-fired water heater system) means that there is more heat stored inside the heating boiler or water heater.

By adding cold water to the very hot water leaving the tankless coil or water heater, we draw hot water out of the water heater itself more slowly than we would without this addition.

Therefore we can expect to draw a larger quantity of (tempered) hot water from the tankless coil on such a system than otherwise. We will have more total domestic hot water for washing and bathing, and we have safer hot water (non-scalding) than if we omitted this pair of controls.

See MIXING / ANTI-SCALD VALVES for a detailed discussion of how to install, set, and use mixing valves, anti-scald valves, or tempering valves on water heating systems to avoid scalding burns and to improve hot water heater performance.

How Can an Anti-Scald Valve Improve the Hot Water Volume & Quantity?

Using an anti-scald valve or "mixing valve" or "tempering valve" on a hot water supply system can increase both the actual and the apparent total quantity of hot water available. That is, building occupants get a longer time in the shower, provided the hot water is used with some sense, as we explain here.

An example of an anti-scald valve installed right at the water heater is provided by Cash Acme Plumbing who provide a "tank booster" anti-scald system - shown here.

[Click to enlarge any image]

We will have more "heat" stored in the hot water tank (or more heat stored inside the heating boiler that in turn is going to heat a tankless coil and thus heat water passing through the coil) if we can keep the hot water tank (or boiler) at a higher temperature.

Watch out: when we heat the hot water tank or boiler to a higher temperature we also increase the chances of someone being scalded at the tap.

Therefore, to avoid scalding, we mix cold in with the outgoing hot water (the right way to do this).

Where a mixing valve is not installed (Watch out for scalding!) we can be smarter at the plumbing fixture itself by turning on less hot water flow and more cold water flow so that the water is not scalding.

This combination of keeping water in the hot water tank (or boiler) hotter, but causing the volume of hot water to flow more slowly at the individual plumbing fixture, mixing in enough cold to get adequate flow quantity and safe temperature, is a risky (scald risk) alternative to using a mixing valve.

We don't recommend this alternative, but we explain it here as you may encounter this approach, especially in an older building and one where there are no small children nor elderly occupants (who are at greater risk of being scalded).

In either case, by starting with a hotter water heater or boiler and by mixing in cold in the outgoing water (or by regulating water pressures at the fixture), we consume hot water in the water heater tank more slowly. That means longer time in the shower.

In sum, with careful installation of appropriate safety controls such as an automatic mixing valve or automatic tempering valve (or by careful use of a manual mixing valve), we can heat water in the water heater storage tank or tankless coil to a higher temperature, mixing or tempering it as it leaves the water heater or at the point of use in the building to avoid scalding.

The result is more total hot water available from the same water heating equipment.

See details at MIX VALVE SCALD PROTECTION, Best Practices

Details about various ways to get more hot water or better hot water pressure and flow are

at HOT WATER IMPROVEMENT where we provide a detailed guide to improving hot water quantity and flow when a tankless coil is installed as well as using other methods of hot water heating.

Watch out: setting water heater temperature higher to attempt to obtain more total hot water at the plumbing fixtures without also installing and properly setting anti-scald devices can result in dangerous, even fatal hot water scalding burns.

• Contact Cash Acme Plumbing: Website: https://www.cashacme.com/contact/ Cash Acme is an RWC Brand. Reliance Worldwide Corporation (Canada) Inc. 74 Alex Avenue Vaughan, Ontario L4L 5X1,
  
  USA: www.cashacme.com Tel: 1-877-700-4242 E-mail: sales@cashacme.com
  
  Canada: www.cashacme.ca Tel: 1-888-820-0120 E-mail: canadasales@rwc.com www.rwc.com

 

Check for and Correct Clogged Piping, Faucets, or Clogged Tankless Coil to Improve Hot Water Pressure or Flow

Hot water pressure and hot water flow in a building may be poor even where a mixing valve has been installed. T

his condition could be due to poor overall building water pressure, due to clogged pipes or due to local clogging in piping or at individual fixtures such as a hot water control valve. .

If cold water pressure is good and hot water pressure is poor, the problem is not an overall building water pressure issue. There is a problem with the hot water system that needs to be found and corrected.

If hot water pressure is poor at just some or just one fixtures,

see HOT WATER PRESSURE LOSS - how to diagnose loss of hot water pressure - look for clogs in the system or at specific plumbing fixtures.

If hot water pressure is strong when the water is first turned on but flow quickly falls off to a weak hot water stream, it's likely that the hot water piping (or tankless coil) are clogged.

Often this repair involves using acid to try to remove minerals that are clogging hot water system piping or a tankless coil, or the tankless coil may need replacement.

Abandoning a tankless coil altogether: When we bought our house the tankless coil was almost totally clogged with minerals, and we figured that it wouldn't provide enough hot water anyway, so we abandoned it.

In the photo at left you can see the round black tankless coil face, with two holes - where we removed the cold-water-in and hot-water-out pipes and simply abandoned the tankless coil. A separate water heater was installed in our utility area. (We'd have preferred an indirect-fired water heater which is discussed later in this article but that's not what we got.)

See TANKLESS COILS for an explanation of how these water heaters work and why they clog up and how to stop clogging up the coil.

See WATER PIPE CLOG REPAIR for a discussion of loss of water pressure due to clogged piping or clogged tankless coils.

At LARGER DIAMETER WATER SUPPLY PIPING we discuss the benefits of using larger diameter water supply piping both to improve water pressure and flow and also to delay the clogging of pipes due to minerals or rust

These Articles Describe the Diagnosis & Repair Steps to Increase Hot Water Pressure or Temperature

Have you already checked our Hot Water Trouble Diagnostic Guide?

As Carson Dunlop Associates ' illustration (left) shows, one way to improve hot water flow in a building is by a larger diameter cold water pipe supplying the hot water heater.

Below we list hot water pressure or temperature diagnosis, repair, and improvement articles. For each item we describe how that topic pertains to hot water temperature and flow.

The list below is in alphabetic order, not in order of priority of things to try. Diagnosis and repair for hot water quantity are explained separately

at HOT WATER QUANTITY IMPROVEMENT.

• ALTERNATIVE HOT WATER SOURCES - besides electric, gas, oil, solar, indirect, & range boilers, are alternatives. Choosing a different way to make hot water can give you more quantity - something you will need inf you are going to increase the hot water flow rate or pressure in your building.
  
  The detailed characteristics of various water heaters themselves, such as life expectancy, cost, safety, and capacity are discussed
  
  at ALTERNATIVE WATER HEATER PROPERTIES
• ANODES & DIP TUBES on WATER HEATERS discusses hot water tank sacrificial anodes and dip tubes whose problems can produce both sulphur smells and even reduced hot water pressure and flow.
  
  Debris from a deteriorated anode or dip tube can clog hot water outlet at a water tank, reducing pressure and flow.
• ANTI_SCALD VALVES & HOT WATER QUANTITY - explains the relationship between devices to prevent scalding burns and the rate of hot water usage.
  
  These devices both improve safety and meter hot water more slowly - makes it last longer, but restricting the hot water flow rate. In short, while it improves hot water safety by preventing scalding burns, the anti-scald valve will also reduce the flow rate (or "pressure" as some put it), thus making hot water last longer.
• AQUASTAT HI LO DIFF SETTINGS - how to set the primary control on a hot water boiler
• CLOGGED PIPING & HOT WATER FLOW - diagnose and correct poor hot water pressure and flow due to pipe clogging. Clogged hot water pipes reduce flow rate through the system, not the total quantity of hot water available. It's easy to diagnose this problem because usually the cold water flow at a given faucet will be noticeably faster than the hot water flow rate.
  
  If both hot and cold flow rates are slow, it could be as simple as a clogged sink faucet strainer, or a bigger problem that we explain
  
  at WATER PRESSURE LOSS DIAGNOSIS & REPAIR.
• ELECTRIC WATER HEATERS - suggestions for inspection, diagnosis, repair. If one heating element on your electric water heater has burned out, expect more tepid hot water (the lower element is still working but the upper one is out), or less quantity of hot water (the upper element works and the lower one is dead).
• EXTRA TANKS to INCREASE HOT WATER - pre-heat your hot water absorbing ambient building heat or increase hot water quantity with cascaded, staged, multiple water heaters, possibly using more than one energy source.
  
  Adding extra tanks can improve both temperature (water is pre-heated) and quantity of hot water.
• GAS FIRED WATER HEATERS - suggestions for inspection, diagnosis, repair include problems that lead to low temperatures and slow recovery rates.
• HIGH EFFICIENCY WATER HEATERS - if replacing a water heater that is leaky, irrepably scale clogged, or just too small, consider a model that saves money in operating cost.
• HOT WATER CIRCULATOR PUMP SPEEDS DELIVERY - hot water pump and loop systems for instant hot water in large buildings.
  
  This won't give you a higher water temperature overall but it will reduce the time between turning on that hot water faucet and when hot water appears.
• HOT WATER PRESSURE IMPROVEMENT - how to diagnose & fix weak hot water flow or pressure
• HOT WATER PRESSURE LOSS - how to diagnose loss of hot water pressure - look for clogs in the system or at specific plumbing fixtures.
• HOT WATER QUANTITY IMPROVEMENT - stop running out of hot water: article on improving hot water quantity, the quantity of hot water in buildings
• MIXING / ANTI-SCALD VALVES includes steps that can extend the availability of hot water, improve water heating efficiency, make hot water safe from scalding, & significantly change the temperature of hot water being delivered at the fixtures
  
  Watch out: for increased hot water scalding burn risk hazards where low-flow shower heads are installed in homes without an anti-scald device.
  
  See MIXING / ANTI-SCALD VALVES
  
  More about hot water usage efficiency is
  
  at EFFICIENCY IMPROVEMENT, HOT WATER
• INDIRECT FIRED WATER HEATERS - allow a larger tank (more hot water) of hot water, heated efficiently by a separate heating boiler. The increased quantity will support piping changes or pressure settings that increase the hot water pressure or flow rate in your building without running out of hot water too quickly.
• INSULATE HOT WATER PIPES - worth doing where piping is accessible, especially on piping running through cool areas, will improve the temperature of hot water delivered to the fixtures, especially during the initial period of use.
• INSULATE the WATER HEATER TANK? - probably not worth doing except in special cases; important safety warnings suggest you should probably not try this.
• LARGER DIAMETER WATER PIPES - worth doing if replacing clogged pipes or building new construction. Increasing water supply piping in even a part of the plumbing system can significantly increase the water flow rate at the fixtures.
• OIL FIRED WATER HEATERS - fast recovery water heaters, suggestions for inspection, diagnosis, repair. Installing a heater that has a faster recovery rate won't increase the water temperature, pressure or flow rate however.
• MIXING / ANTI-SCALD VALVES - can not only avoid scalding hot water dangers, but can meter hot water usage to give a longer bathing shower time.
  
  The temperature of water delivered at a plumbing fixture is directly controlled by these devices.
• MULTIPLE WATER HEATERS in PARALLEL to increase total hot water quantity
• MULTIPLE WATER HEATERS in SERIES to stage hot water heating for varying levels of demand
• RANGE BOILER WATER HEATER an older form of indirect-fired hot water heating used with separate heating boilers
• SIDE ARM COIL WATER HEATER similar to instantaneous and tankless coil water heaters, often used with range boilers
• SOLAR HOT WATER HEATERS - lower energy cost, effective hot water source in sunny climates
• TANKLESS COIL HOT WATER INCREASE - various tricks can significantly improve the safety and water quantity available
• TANKLESS WATER HEATERS - no hot water tank tank, no standby losses, just hot instant hot water, at various flow rates
• WATER HEATER TEMPERATURE TOO COLD or TOO HOT - where to look for problems when the "hot water" is not hot enough
• WATER HEATER COMPARISONS, PROPERTIES The characteristics of various water heaters such as life expectancy, cost, safety, and capacity
• WATER HEATER SCALE DE-LIMING PROCEDURE explains how mineral scale build-up in a water heater (or in building water piping) can result in both poor hot water quantity and
• WATER HEATER SCALE PREVENTION explains how to prevent lime and scale formation in water heating equipment.
  
  Scale formation in the water heater may explain a reduction in hot water temperature, hot water quantity, or hot water heating appliance noises: popping, banging, crackling sounds.
• WATER HEATER SIZE SPECIFICATION - how do we determine the necessary water heating capacity for a building? How much hot water do different occupants and building types use?
• WATER PRESSURE LOSS DIAGNOSIS & REPAIR - overall guide to improving building water pressure
• HOT WATER QUANTITY IMPROVEMENT - discusses getting more total quantity of hot water for a building
• WATER SOFTENERS & CONDITIONERS - how to install and adjust a water softener to avoid hot water piping or tankless coil clogging due to hard water and minerals

A Comparison of Alternative Hot Water Heaters & Sources

The following articles discuss alternative ways to produce domestic hot water for washing and bathing.

• HIGH EFFICIENCY HOT WATER HEATERS such as direct-vent gas-fired water heaters
• INDIRECT-FIRED HOT WATER HEATERS which use a separate heating boiler to produce a larger quantity of hot water
• INSTANTANEOUS WATER HEATERS point of use systems that have little or no standby energy losses
• MULTIPLE WATER HEATERS in PARALLEL to increase total hot water quantity
• MULTIPLE WATER HEATERS IN SERIES to stage hot water heating for varying levels of demand
• RANGE BOILER WATER HEATER an older form of indirect-fired hot water heating used with separate heating boilers
• SIDE ARM COIL WATER HEATER similar to instantaneous and tankless coil water heaters, often used with range boilers
• SOLAR WATER HEATERS using solar collectors, an indoor water tank, pump and controls, using minimal "on-grid" energy
• TANKLESS COILS - using a coil in the heating boiler or in an indirect heated water tank to produce domestic hot water
• TANKLESS COIL HOT WATER INCREASE a heat exchanging coil immersed inside of a heating boiler heats provides (somewhat limited) hot water. various tricks can significantly improve the safety and water quantity available

Thanks to Carson Dunlop Associates, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article.

...

---

---

ADVERTISEMENT

---

---

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2019-07-03 by (mod) - very poor hot water pressure but good cold water pressure through the house

We need to start by identifying the type of hot water equipment in your building. That's because the point of the problem will be different on different types of equipment. For example if your hot water is made by a tankless coil a coil may be clogged by minerals from hard water.

But if your hot water is made by a separate water tank, calorifier, or geyser or hot water cylinder, those are all terms for the same thing depending on where you live, and the problem could be a clogged dip tube or valve at the water heater

On 2019-06-26 by Arnie

very poor hot water pressure but good cold water pressure through the house. Where should I start to look?

On 2019-01-22 - by (mod) -

Kevin

That's an interesting question and I'm very interesting hypothesis. I'll have to do some more reading myself about the location of the anti-scald or mixing valve.

But I agree that if a mixing valve is not working correctly it could be intermittently delivering the wrong temperature of hot water.

On 2019-01-22 by Kevin

I have a peerless wbv-03 boiler with a tankless coil. The hot water has never really been right but now it is worse. It seems to be during shower use is then I have the problem or notice it. The water starts out as cool then gets worm after a few seconds then goes to lukewarm after about a minute.

The sinks seem to do the same but after a long time since they are not using the water as fast. I have checked to coil and water seems to be going thru it freely. I have been looking at the installation manual at the piping schematic for the mixing valve.

The valve should be a minimum of 12 inches below the center of the coil and it is only 6 inches. Could this be affecting the hot water?

On 2018-06-02 - by (mod) -

Mike

My best suggestions for improving hot water pressure (flow rate at the taps) are in the article above. You will want to diagnose the problem as best you can before choosing a solution.

The notes above on this page are more-complete than an off-the-cuff reply.

Please take a look, then ask what questions occur to you.

Thanks

On 2018-06-02 by Mike

Low Hot Water Pressure

On 2016-12-24 by Lou Santoro

recently our manual domestic hotwater lines cold water feed was replaced with a cone shaped valve similar looking to car engines radiatorcone shaped themastat/ on top is a allen head adjustment set screw ? Is this a new cold water make up water control valvea/

On 2016-12-23 - by (mod) -

Anon: if water is plenty hot elsewhere I suspect the water is losing heat while passing through a long run of piping or through pipes in an un-heated area. The least-costly improvement is to insulate those hot water pipes.

On 2016-12-11 by Anonymous

How do I get hotter water in my kitchen sink in my apartment building?

On 2016-01-10 by ben

can i change my burner from 40000 to 50000 btu on a home water tank?

...

Continue reading  at HOT WATER QUANTITY IMPROVEMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• WATER HEATER COMPARISONS, PROPERTIES
• HOT WATER IMPROVEMENTS - home
  • ALTERNATIVE HOT WATER SOURCES
  • GAS HEATERS, HIGH EFFICIENCY
  • HOT WATER CIRCULATOR PUMP SPEEDS DELIVERY
  • HOT WATER EFFICIENCY IMPROVEMENT
  • HOT WATER PRESSURE IMPROVEMENT
  • HOT WATER PRESSURE LOSS
  • HOT WATER QUANTITY IMPROVEMENT
  • INSULATE HOT WATER TANK?
  • MULTIPLE GANGED TANKLESS WATER HEATERS
  • TANKLESS WATER HEATERS
  • TANKLESS COIL HOT WATER INCREASE
  • WATER CONSERVATION MEASURES
  • WATER HEATER COMPARISONS, PROPERTIES
  • WATER HEATER SIZE SPECIFICATION
  • WATER HEATER STANDBY LOSSES
  • WATER HEATER TEMPERATURE TOO COLD or TOO HOT
• WATER HEATER PROBLEM DIAGNOSIS
• WATER HEATER SCALE PREVENTION
• WATER HEATER TEMPERATURE ADJUSTMENT CONTROLS - home

Suggested citation for this web page

HOT WATER IMPROVEMENTS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to WATER HEATERS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Questions & answers or comments about improving hot water quantity or temperature in building plumbing systems

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---