How to Get More Hot Water Pressure or Temperature from a Water Heater or Tankless Coil

How to improve hot water pressure , flow rate, & how to improve hot water temperature - How to stop running out of hot water, How to make hot water hot enough; 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
ALTERNATIVE HOT WATER SOURCES & Methods - separate article
CLOGGED PIPING & Hot Water Flow - separate article
HOT WATER IMPROVEMENTS
HOT WATER DELIVERY SPEED UP - separate article
HOT WATER PRESSURE LOSS - separate article
HOT WATER QUANTITY IMPROVEMENT - separate article
INSULATE HOT WATER TANK? - separate article
Questions & Answers about improving hot water pressure or temperature in building water heater systems
References

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This article explains how to improve the hot water pressure or temperature in a building. We list decribe detailed procedures for diagnosing and fixing the various causes of either hot water that is too weak in flow (bad pressure) or hot water that is not hot enough.

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

Thanks to Carson Dunlop, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Before you start fixing or buying stuff to fix a hot water problem hot water problems and diagnostic guides for all kinds of hot water troubles are summarized at WATER HEATER PROBLEM DIAGNOSIS. You might want to check there to be sure you're fixing the right problem.

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. Please Contact Us if you think we should re-order or add to this list.

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.
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 - improve safety and meter hot water more slowly - makes it last longer, but restricting the hot water flow, while it improves temperature, will reduce the flow rate (or "pressure" as some put it).
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 DELIVERY SPEED UP - 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 LOSS - how to diagnose sudden loss of hot water pressure
HOT WATER QUANTITY IMPROVEMENT - article on improving hot water quantity, pressure and flow - the quantity of hot water in buildings
Hot water usage efficiency improvements, such as installing MIXING / ANTI-SCALD VALVES include steps that can 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 Piping - 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 Hot Water Tank? - probably not worth doing except in special cases; important safety warnings suggest you should probably not try this.
Larger Diameter Water Supply Piping - 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 Heaters an older form of indirect-fired hot water heating used with separate heating boilers
Side Arm Coil Water Heaters 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
Temperature of Hot Water is Too Low - where to look for problems when the "hot water" is not hot enough
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
WATER PRESSURE LOSS DIAGNOSIS & REPAIR - overall guide to improving building water pressure
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

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

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.

Check for and Correct Clogged Piping 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. This condition could be due to poor overall building water pressure or due to clogged pipes.

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 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 guide 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

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.Water Pressure Loss - Diagnosis how to determine why water pressure has been lost or why there is no water at all in a building
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