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This article explains how to improve the hot water pressure, quantity, flow, and water temperature safety in a building. We explain how to increase the hot water quantity and flow obtained from a tankless coil as well as other methods of making domestic hot water.

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.

• If you have no hot water at all, but cold water comes out of the hot water faucets, make sure that your water heater has fuel (oil or gas) or power (electric, solar). Also check for a defective high temperature limit switch (there is a reset switch on the thermostat) or for a defective upper thermostat (you'll have tepid hot water but no HOT water). See NO HEAT - NO HOT WATER: HEATER DIAGNOSIS for details about troubleshooting when you have no hot water at all.
• If your problem is gradual or long-standing poor hot water quantity, pressure, or flow, start your diagnosis HOT WATER IMPROVEMENTS or see HOT WATER QUANTITY IMPROVEMENT.
• If hot water pressure has suddenly been lost but you still have some, poor hot water flow, see HOT WATER PRESSURE LOSS
• If you want to speed the delivery of hot water to plumbing fixtures or if the recovery rate of your water heater is too slow, if the water heater is electric check for a defective upper or lower heating element. See HOT WATER DELIVERY SPEED UP for details.
• If your concern with total water pressure and flow, both hot and cold, see WATER PRESSURE LOSS DIAGNOSIS & REPAIR, and if you simply run out of water, both hot and cold, see WATER QUANTITY IMPROVEMENT.
• If your hot water heating costs are too high check for:
  • The hot water thermostat is set unnecessarily high - see the thermostat on the control or aquastat for your oil or gas fired water heater or tankless coil boiler; or see Electric Water Heater Thermostats
  • The hot water heater tank has a sediment or scale problem - see SCALE REMOVAL, WATER HEATERS
  • Check for long hot water piping runs, especiallyi if the piping is also not insulated and/or runs through cold areas, or if hot water supply piping was routed through exterior building walls (exposed to low temperatures)
  • Check for building occupants who waste hot water - long showers, baths, leaving the kitchen sink hot water running continuously; also check for leaky hot water faucets in the building or for wrong piping connections (we found a running toilet that had been connected to hot water instead of cold water piping)
  • Check for a water heater that is too small for the building it serves - causing it to run continuously
  • Check for a water heater thermostatic control that is out of calibration - keeping water hotter than its setting

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

How do we Improve the Hot Water Volume & Quantity?

As we discussed beginning in the previous section of this article, there are several different hot water problems:

1. Poor hot water flow, or bad hot water pressure, which is usually a piping or clogging problem, mineral clogging at a water tank or tankless coil, 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. Poor hot water quantity can also be caused by mineral deposits and clogging in a hot water tank.
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. See Temperature of Hot Water is Too Low for steps to correct water that just won't get hot at all or won't get hot enough.

These Articles Describe the Diagnosis & Repair Steps to Increase Hot Water Quantity

The articles listed below offer more details about steps one can take to increase hot water quantity, pressure, and flow in a building. Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. 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 diagnosis, repair, and improvement articles.

• ALTERNATIVE HOT WATER SOURCES - besides electric, gas, oil, solar, indirect, & range boilers, are alternatives
• 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.
• Anti-Scald Valves & Hot Water Quantity - improve safety and meter hot water more slowly - makes it last longer
• CLOGGED PIPING & Hot Water Flow - diagnose and correct poor hot water pressure and flow due to pipe clogging
• ELECTRIC WATER HEATERS - suggestions for inspection, diagnosis, repair
• 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
• GAS FIRED WATER HEATERS - suggestions for inspection, diagnosis, repair
• High Efficiency Water Heaters - if replacing a water heater, 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
• HOT WATER PRESSURE LOSS - how to diagnose sudden loss of hot water pressure
• HOT WATER QUANTITY IMPROVEMENT - article on improving hot water pressure and flow - the quantity of hot water in buildings
• Hot water usage efficiency improvements:
  • Change home appliances and plumbing fixtures to install devices that consume less hot water. For example, replace showerheads that have a flow rate greater than 2.5 gallons per minute (the current National Energy Policy Act standard), but
    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
  • Take shorter showers,
  • When replacing a clothes washer, install models that use less water by installing a high efficiency washing machine with a "low water factor" and always wash full loads rather than smaller loads in your washing machine
• INDIRECT FIRED WATER HEATERS - allow a larger tank of hot water, heated efficiently by a separate heating boiler
• Insulate Hot Water Piping - worth doing where piping is accessible, especially on piping running through cool areas
• Insulate Hot Water Tank? - probably not worth doing except in special cases; important safety warnings
• Larger Diameter Water Supply Piping - worth doing if replacing clogged pipes or building new construction
• OIL FIRED WATER HEATERS - fast recovery water heaters, suggestions for inspection, diagnosis, repair
• 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
• 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.

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 Water Heaters such as direct-vent gas-fired water heaters
• Indirect-fired 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 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 Water Heaters using solar collectors, an indoor water tank, pump and controls, using minimal "on-grid" energy
• Tankless Coil for Hot Water 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

The characteristics of various water heaters such as life expectancy, cost, safety, and capacity are discussed at WATER HEATER PROPERTIES

Ways to improve total hot water quantity, pressure, temperature and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.

Questions & Answers regarding this article

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

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

HOT WATER IMPROVEMENTS
HOT WATER DELIVERY SPEED UP
HOT WATER PRESSURE EXPANSION RATE
HOT WATER PRESSURE LOSS

HOT WATER QUANTITY IMPROVEMENT
  Alternative Hot Water Sources & Methods
  Anti-Scald Valves & Hot Water Quantity
  CLOGGED PIPING & Hot Water Flow
  Extra Tanks to Increase Hot Water
  Insulate Hot Water Piping
  Insulate Hot Water Tank?
  Larger Diameter Water Supply Piping
  Water pipe clog diagnosis
  Water pipe clog repair guide

ALTERNATIVE HOT WATER SOURCES
  Electric Shower Heaters
  High Efficiency Water Heaters
  Indirect-fired Water Heaters
  Instantaneous Water Heaters
  Multiple water heaters in parallel
  Multiple water heaters in series
  Range Boiler Water Heaters
  Side Arm Coil Water Heaters
  Solar Water Heaters

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• 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.

• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• HOT WATER HEATERS - a detailed guide to all types of hot water sources, problems, inspection, repair
• Water Pressure Loss - Diagnosis how to determine why water pressure has been lost or why there is no water at all in a building
• Water pump and pressure tank repair diagnosis & cost an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
• Water pressure tank failures & water pump short cycling diagnosis and repair
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