Like many other household conveniences, a good supply of hot water is only truly appreciated when it stops. And if it stops when you're in the shower, this realization can arrive quite abruptly. Fortunately, it doesn't happen that often. The systems that provide hot water are generally reliable and operate for years without a hitch. But when the hitch comes, some background can help. Even if you can't make the repairs yourself, you'll have a good idea what to tell the doctor when he arrives.

1. Hot Water Maker
2. Hot Water Heater Troubleshooting
3. How Does A Combination Hot Water Cylinder Work On Iphone

Most homes have a tank-type water heater. If you find a large, cylindrical tank standing on end with pipes attached to it, you have a tank-type system. If you don't find a tank, but you have a hot-water heating system that heats your home, it's likely that the hot water reaching your taps is heated bythe boiler. In other cases, hot water may be supplied by a stand-alone instantaneous water heater that's mounted near the fixture it serves.

Tank-Type Water Heaters

As with a standard vented system, a combination storage system relies on gravity to supply hot water to the taps and shower(s). As the cold water cylinder is located directly above the hot water cylinder, this means that the generated 'head' of water pressure is relatively low. Vented hot water cylinder system. Water in the cylinder is topped up from the header tank in the loft which in turn is kept topped from the mains. Water in the cylinder is heated either by an electric immersion heater (direct) and/or by the central heating boiler (in-direct). Hot water in the cylinder is used to supply the hot taps.

The standard water heater comes in two flavors: electric and fuel-fired. In the latter, the fuel most commonly used is gas, either natural or propane, but oil-fired heaters are popular in many areas. Fuel-fired units have a vent pipe at the top to carry away exhaust gases. Electric models, on the other hand, simply have a power cable that connects the heater to your electric service panel.

The job of the tank-type heater is not only to heat the water, but to store it until it's ready to use. Therefore, in addition to the tank's heating system, every tank is equipped with insulation to help keep the water warm between heating cycles.

On top of every tank you'll find the water supply and delivery pipes. The supply pipe routes cold water to the bottom of the tank through the dip tube. The hot-water delivery pipe takes water from the top. For safety, all water heaters are equipped with a T&P valve (temperature-and-pressure relief valve). This valve opens if either the temperature or pressure of the water exceeds a safe limit. The valve is connected to a pipe that runs down the outside of the tank, ending about 6 in. from the floor. It's a good idea to keep a bucket under the end of the pipe to catch water if the valve opens. The T&P valve should not be connected to a drain. If the valve did open, a sign that a problem exists, you might never know that it had opened.

Most tanks are made of steel, which is glass-lined on the inside to help prevent corrosion. In fact, corrosion is the primary reason that tanks fail. Once rust produces a hole, there are temporary fixes, but the tank should be replaced. All tanks also have an anode rod to control corrosion. The magnesium anode rod protects the tank by corroding in place of the steel. Because the rod is designed to corrode, it will eventually wear away. After this happens, corrosion of the steel accelerates. It's a good idea to check the anode rod once a year, and replace it if necessary. At the bottom of every tank is a drain cock to empty the heater, and a valve on the supply pipe allows you to shut down the hot-water plumbing without affecting the cold-water supply to the house.

Electric Water Heaters

The typical electric unit is wired to a 220-volt circuit. To heat the water, the current passes through electrical-resistance heating elements—usually two, one at the middle of the tank and one at the bottom.

Power is delivered to each element through a thermostat—a switch that senses the water temperature. When the temperature drops, the switch closes to allow current flow, and it opens when the temperature reaches its preset limit. Thermostats have a dial for setting the maximum water temperature—generally between 130 degrees and 140 degreesF, or as low as about 120 degreesF for increased energy savings and scald protection.

When a hot-water tap is opened, cold water enters the tank through the dip tube and the drop in temperature triggers the thermostat and element at the bottom. As the water at the top of the tank is replaced by cool water, the temperature at the top thermostat drops and its element kicks in. When the tap is turned off, the heating elements continue to carry current until the thermostats are satisfied.

Fuel-Fired Water Heaters

Instead of electrical-resistance elements, gas-fired heaters have a burner that's fed gas through a control valve and a thermostat switch. In an oil-fired heater, the burner is similar to that found on an oil-fired furnace. In either case, the burner is usually situated to throw a flame under the tank. The exhaust gases are vented either through a hollow core at the center of the tank or around the tank sides. Because fuel-fired heaters heat the tank, which in turn heats the water, there will be more wear and tear on the tank than with electric heat. A fuel-fired heater, therefore, may have a shorter life expectancy than an electric heater.

Heater Effectiveness

Because water heaters both heat and store water, the rate at which the water is heated and the capacity of the tank affect the supply of hot water at your fixtures.

The speed at which a unit heats water is called its recovery rate. This figure indicates the amount of water in gallons that can be heated to 100 degreesF in 1 hour. Once you draw water faster than it's heated, the temperature drops.

However, because the tank stores hot water, its capacity also affects the ongoing availability at the tap. Choosing a water heater that has an appropriate capacity and recovery rate depends on how much water your home demands and how your unit heats the water. Typically, heaters with low recovery rates have a high tank capacity. Although it takes longer to heat the water, there's more of it for intermittent use. Electric heaters fall into this category. On the other hand, a fuel-fired heater with a high recovery rate needn't have a large tank, because it can heat the water faster. In general, electric models have the lowest recovery rate, and oil-fired units have the highest.

Tankless Heaters

If your home doesn't have a hot-water tank, you probably have a hot-water or steam home-heating system that also heats water for your taps. To accomplish the job, your boiler has a tankless water heater. In this system, a coil of pipe is connected at one end to the cold water supply, and at the other to your hot-water delivery piping. As the boiler heats the water that warms your home, that water heats the coil, creating hot water at your taps.

Because tankless heaters only heat water as it's used, there's no cost for maintaining heat in a large volume of water during periods of low usage. However, they do have a few drawbacks. First, the hot water generated is far hotter than necessary, so a cold-water mixing valve should be installed to reduce the chance of scalding. Second, the boiler must fire to generate hot water—which is efficient during the winter months, but decidedly more wasteful when the weather is warm. Like tank-type heaters, tankless heaters are designed to achieve a specific heating rate. Once the rate is exceeded by demand, the temperature of the water drops. In some cases, storage tanks are connected to the heating coil to increase hot-water availability.

In addition to boiler-mounted tankless heaters, stand-alone units are available. Gas-fired instantaneous water heaters utilize a coil and heat exchanger to heat water as it's required. Like boiler-mounted units, instantaneous water heaters don't use energy to maintain the heat in a volume of water, but only fire as hot water is required. A downside is that stand-alone units typically have a lower flow rate than boiler-mounted systems and may fall short during periods of high demand.

A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.

Water is a convenient heat storage medium because it has a high specific heat capacity. This means, compared to other substances, it can store more heat per unit of weight. Water is non-toxic and low cost.

An efficiently insulated tank can retain stored heat for days, reducing fuel costs.^[1] Hot water tanks may have a built-in gas or oil burner system, electric immersion heaters. Some types use an external heat exchanger such as a central heating system, or heated water from another energy source. The most typical, in the domestic context, is a fossil-fuel burner, electric immersion elements, or a district heating scheme.^[2]

Water heaters for washing, bathing, or laundry have thermostat controls to regulate the temperature, in the range of 40 to 60 °C (104 to 140 °F), and are connected to the domestic cold water supply.

Where the local water supply has a high content of dissolved minerals such as limestone, heating the water causes the minerals to precipitate in the tank (scaling). A tank may develop leaks due to corrosion after only a few years, a problem exacerbated by dissolved oxygen in the water which accelerates corrosion of both tank and fittings.

Insulation[edit]

Typically hot water storage tanks are wrapped in heat insulation to reduce energy consumption, speed up the heating process, and maintain the desired operating temperature. Thicker thermal insulation reduces standby heat loss. Water heaters are available with various insulation ratings but it is possible to add layers of extra insulation on the outside of a water heater to reduce heat loss. In extreme conditions, the heater itself might be wholly enclosed in a specially constructed insulated space.

The most commonly available type of water heater insulation is fiberglass, fixed in place with tape or straps or the outer jacket of the water heater. Insulation must not block air flow or combustion gas outflow, where a burner is used.

In extremely humid locations, adding insulation to an already well-insulated tank may cause condensation leading to rust, mold, or other operational problems so some air flow must be maintained, usually by convection caused by waste heat, but in particularly humid conditions such ventilation may be fan-assisted.

Most modern water heaters have applied polyurethane foam (PUF) insulation.^{[citation needed]} Where access to the inner tank is a priority (in cases of particularly aggressive minerals or oxygen levels in the local water supply) the PUF can be applied in encapsulated form, allowing the removal of insulation layer for regular integrity checks and if required, repairs to the water tank.

Solar hot water storage tank[edit]

In a solar water heating system, a solar hot water storage tank stores heat from solar thermal collectors.^[3] The tank has a built-in heat-exchanger to heat domestic cold water. In relatively mild climates, such as the Mediterranean, the (heavily insulated but metal-wrapped) storage tanks are often roof-mounted. All such tanks share the same problems as artificially-heated tanks including limestone deposit and corrosion, and suffer similar reductions in overall efficiency unless scrupulously maintained.

Water tank leakage[edit]

Water heater tanks may be made of vitreous enamel-lined carbon steel, stainless steel, or copper.

While copper and stainless steel domestic hot water tanks are more commonplace in Europe, carbon steel tanks are more common in the United States, where typically the periodic check is neglected, the tank develops a leak whereupon the entire appliance is replaced.^[4] Even when neglected, carbon steel tanks tend to last for a few years more than their manufacturer's warranty, which is typically 3 to 12 years in the US.^{[citation needed]}

Hot Water Maker

Vitreous-lined tanks are much lower in initial cost, and often include one or more sacrificial anode rods designed to protect the tank from perforation caused by corrosion^[5] made necessary since chlorinated water is very corrosive to carbon steel. As it is very nearly impossible to apply any protective coating perfectly (without microscopic cracks or pinhole defects in the protective layer)^[6] manufacturers may recommend a periodic check of any sacrificial anode, replacing it when necessary.

Some manufacturers offer an extended warranty kit that includes a replacement anode rod. Because conventional hot water storage tanks can be expected to leak every 5 to 15 years, high-quality installations will include, and most US building/plumbing codes now require, a shallow metal or plastic pan to collect the seepage when it occurs.

Hot water storage tank with closed water circuit[edit]

This method stores heat in a tank by using external heat-exchangers (coils) that can be directly tapped or used to power other (external) heat-exchangers.

The chief benefit is that by avoiding drawing-off domestic hot water directly, the tank is not continually fed with cold water, which in 'hard' water areas reduces the deposit of limescale to whatever is dissolved in the original charge of water plus relatively trivial amounts added to replace losses due to seepage.

Hot Water Heater Troubleshooting

An added benefit is reduced oxygen levels in such a closed system, which allows for some relaxation in the requirements for materials used in the hot water storage tank and the closed water circuits, external heat exchangers, and associated pipework.

While an external heat exchanger system used for domestic hot water will have mineral deposits, descaling agents extend the life of such a system.

Stratified hot water storage tank with closed water circuit[edit]

For an illustration - see reference^[7]

Another method to store heat in a hot water storage tank has many names: Stratified hot water storage tank with closed water circuit, stratified thermal storage, thermocline tank and water stratified tank storage but in all cases the significant difference is that pains are taken to maintain the vertical stratification of the water column, in other words to keep the hot water at the top of the tank while the water at the bottom is at a distinctly lower temperature.

This is desirable in places with a wide climatic range where summer cooling is as important as heating in winter, and entails one or more of the following measures:

How Does A Combination Hot Water Cylinder Work On Iphone

• Different heating and cooling loops must send the heated or cooled water in with as low a velocity as possible. (This necessarily entails heating and cooling loops having velocity controlled pumps and tube ports with the maximum feasible diameter.)
• For cooling applications, cool water is sent out from the bottom and warm (return) water is fed in at the top.
• Heating applications get hot water out at the top and return cool water to the bottom.
• 'Stratification-enhancing' devices within the hot water storage tank (but if the water inlet velocity is as low as possible this might not be needed).
• A more advanced heat control system^[8] is required.

When a stratified hot water storage tank has closed water circuits, the water temperatures can be up to 90 to 95 °C at the top and 20 to 40 °C at the bottom. Calm, undisturbed water is a relatively poor heat conductor when compared to glass, bricks and soil.

(Illustrated by a still lake, where the surface water can be comfortably warm for swimming but deeper layers be so cold as to represent a danger to swimmers, the same effect as gives rise to notices in London's city docks warning 'Danger Cold Deep Water).

Accordingly, an arbitrary volume of hot water can be stored, as long as the stratification is kept intact. In this case there must not be vertical metal plates or tubes as they would conduct heat through the water layers, defeating the purpose of stratification. When effectively employed this technique can maintain water as high as 95 °C (i.e. just below boiling) yielding a higher energy density, and this energy can be stored a long time provided the hot water remains undiluted.

Depending on the purpose of the installations, water exchanges tapping different levels allow water temperatures appropriate to the required use to be selected.^[7]

In many solar heating systems the energy parameters can be read as a function of time, from the 'dwell' time necessary to transform daylight into heat, at its peak the maximum hot water temperature near the top of the tank.^[1]

Dual element electric[edit]

When flow starts from the uppermost outlet, cold water enters the tank at the bottom. This drop in temperature causes the thermostat to switch on the electric heating element at the bottom of the tank. When the water at the top of the tank is drawn off the hot water at the top is displaced by relatively cooler water, the top thermostat turns the top element on. When the flow stops, the elements stay on until their settings are met.^[9]

While it is common to have the top and bottom thermostats set differently in order to save energy, the fact that hot water rises means the thermostat controlling the upper element should feed the hottest supply, while the lower element the warmest.

If the thermostats in such a system are reversed - warm feed from the top, hot from the center - it may not only affect the energy efficiency of the system, feeding scalding water to a domestic hot water outlet may be dangerous, or if directed to warm-feed washers damage them beyond repair.

Safety issues[edit]

Hot water can cause painful, dangerous scalding injuries, especially in children and the elderly. Water at the outlet should not exceed 49 degrees Celsius. Some jurisdictions set a limit of 49 degrees on tank setpoint temperature. On the other hand, water stored below 60 degrees Celsius can permit the growth of bacteria, such as those that cause Legionnaire's disease, which is a particular danger to those with compromised immune systems. One technical solution would be use of mixing valves at outlets used for sinks, baths or showers, that would automatically mix cold water to maintain a maximum below 49 C. A proposal to add this to the building code of Canada was unsuccessful. ^[10]

See Also[edit]

References[edit]

1. ^ ^abinvest-tools.com: Graphs, Main page and description: Overview of the DHW system, The water tank (heat reservoir) Quote: '...With the tank there came a 10 cm 'soft foam' isolation that fulfills the minimum insulation requirements...So after several months, I added another round of 16 cm aluminum coated glass wool, and now the tank stores enough heat for about 7 or 8 days when it is full loaded (temperature range is 95°C down to 40°C)...'
2. ^'District Heating from Wind: Kirkwall'. University of Strathclyde Engineering. Retrieved 20 January 2016.
3. ^.Brian Norton (2011) Solar Water Heaters: A Review of Systems Research and Design Innovation, Green. 1, 189–207, ISSN (Online) 1869-8778
4. ^Schuyler, Randy. 'The Basics: What kills water heaters'. Water Heater Rescue. waterheaterrescue.com. Retrieved 2012-03-31.
5. ^Schuyler, Randy. 'The Basics: Anodes and Longevity'. Water Heater Rescue. waterheaterrescue.com. Retrieved 2012-03-31.
6. ^Schuyler, Randy. 'The Basics: Choosing a water heater'. Water Heater Rescue. waterheaterrescue.com. Retrieved 2012-03-31.
7. ^ ^abSolar heating system with stratified hot water storage tank with closed water circuit and the possibility of reading many current parameters: solar.webseiten.cc: Live-Daten Holzhausen
8. ^Technische Alternative: Freely programmable universal controller UVR1611, Manuals and firmware in English and German: downloads, Programing examples: UVR-Beispielsammlung, Practical examples on solar heating systems with hot water storage tanks with current measuring date: Livedaten
9. ^'How It Works: Water Heater'. Popular Mechanics. Retrieved 26 November 2014.
10. ^https://canadasafetycouncil.org/home-safety/heated-debate-about-hot-water