Conventional Storage Water Heaters
Conventional storage water heaters remain the most popular type of water heating system for the home. Here you'll find basic information about how storage water heaters work; what criteria to use when selecting the right model; and some installation, maintenance, and safety tips.
How They Work
A single-family storage water heater offers a ready reservoir—from 20 to 80 gallons—of hot water. It operates by releasing hot water from the top of the tank when you turn on the hot water tap. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full.

 

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Heating and Cooling Tips
Set your thermostat as low as is comfortable in the winter and as high as is comfortable in the summer. Clean or replace filters on furnaces once a month or as needed.

~ Clean warm-air registers, baseboard heaters, and radiators as needed; make sure they're not blocked by furniture, carpeting, or drapes.

~ Bleed trapped air from hot-water radiators once or twice a season; if in doubt about how to perform this task, call a professional.

~ Place heat-resistant radiator reflectors between exterior walls and the radiators.

~ Turn off kitchen, bath, and other exhaust fans within 20 minutes after you are done cooking or bathing; when replacing exhaust fans, consider installing high-efficiency, low-noise models.

~ During the heating season, keep the draperies and shades on your southfacing windows open during the day to allow the sunlight to enter your home and closed at night to reduce the chill you may feel from cold windows.

~ During the cooling season, keep the window coverings closed during the day to prevent solar gain.

$ Long-Term Savings Tip: Select energy-efficient products when you buy new heating and cooling equipment. Your contractor should be able to give you energy fact sheets for different types, models, and designs to help you compare energy usage. For furnaces, look for high Annual Fuel Utilization Efficiency (AFUE) ratings. The national minimum is 78% AFUE, but there are ENERGY STAR models on the market that exceed 90% AFUE.

$ Long-Term Savings Tip: For air conditioners, look for a high Seasonal Energy Efficiency Ratio (SEER). The current minimum is 13 SEER for central air conditioners. ENERGY STAR models are 13 SEER or more. The American Council for an Energy-Efficient Economy provides tips for buying energy-efficient furnaces, boilers, AC units, and heat pumps

 

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Heating, Ventilation and Air Conditioning
How much energy can I save by using fans instead of my air conditioner?

The basic notion is that moving air (from ceiling, whole-house, or portable fans) makes you feel cooler, so you can turn up the air conditioner thermostat or turn it off altogether. Whole-house fans are a potential substitute for air conditioning, since they move large amounts of air through the house and require open windows. Savings from using a whole-house fan can be large (it uses 20% or less of the energy of a central air conditioner on a per-hour basis, although they usually need to be used for fewer hours). Also a whole-house fan provides good comfort levels when it's not too humid or too hot outside (night time). Studies by the Florida Solar Energy Center (FSEC) show that ceiling fans can save energy *if the occupants turn up the A/C thermostat*. Unfortunately, most people don't adjust the thermostat. Often people leave them on even when no one is home, which can result in negative savings.
Research from FSEC indicates that whole-house fan savings are quite variable, ranging from about 10% to 65%. This range is due to the effect of climate; a milder climate will see savings toward the upper end of that range. FSEC found that if the air conditioning thermostat is set 2o F higher when using ceiling fans, the savings will be 14%. (With a higher thermostat setting, savings are higher.) If the thermostat setting is not changed, electricity consumption will actually increase by 15%. FSEC's survey of actual behavior showed no measurable savings from cooling fans (i.e. in energy terms, the ceiling fan and the A/C were a wash). There is at least one efficient ceiling fan that uses less energy and has an occupancy sensor (on some models).

 

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Maintaining Your Air Conditioner
An air conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance while energy use steadily increases.
Air Conditioner Filters
The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Keeping the filter clean can lower your air conditioner's energy consumption by 5%–15%.
For central air conditioners, filters are generally located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself. Room air conditioners have a filter mounted in the grill that faces into the room.
Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.
Air Conditioner Coils
The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil, reducing its ability to absorb heat. To avoid this problem, check your evaporator coil every year and clean it as necessary.
Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins.
You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.
Coil Fins
The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.
Condensate Drains
Occasionally pass a stiff wire through the unit's drain channels. Clogged drain channels prevent a unit from reducing humidity, and the resulting excess moisture may discolor walls or carpet.

 

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Selecting a New Water Heater
You have a lot to consider when selecting a new water heater for your home. You should choose a water heating system that will not only provide enough hot water but also that will do so energy efficiently, saving you money. This includes considering the different types of water heaters available and determining the right size and fuel source for your home.
Types of Water Heaters
It's a good idea to know the different types of water heaters available before you purchase one:
· Conventional storage water heaters
Offer a ready reservoir (storage tank) of hot water (most common)
· Demand (tankless or instantaneous) water heaters
Heat water directly without the use of a storage tank (becoming more popular)
· Heat pump water heaters
Move heat from one place to another instead of generating heat directly for providing hot water
· Solar water heaters
Use the sun's heat to provide hot water
· Tankless coil and indirect water heaters
Use a home's heating system (boiler) to heat water.
Selection Criteria
When selecting the best type and model of water heater for your home, you also need to consider the following:
· Fuel type, availability and cost
The fuel type or energy source you use for water heating will not only affect the water heater's annual operation costs but also its size and energy efficiency.
· Size
To provide your household with enough hot water and to maximize efficiency, you need a properly sized water heater.
· Energy efficiency
To maximize your energy and cost savings, you want to know how energy efficient a water heater is before you purchase it.
· Costs
Before you purchase a water heater, it's also a good idea to estimate its annual operating costs and compare those costs with other less or more energy-efficient models.

Reading List
· Krigger, J.; Dorsi, C. (2004). Residential Energy: Cost Savings and Comfort for Existing Buildings. Helena, MT: Saturn Resource Management.
· Water Heating (PDF 836 KB). (August 2001). DOE/GO-102001-0785. U.S. Department of Energy.
· Home Energy Briefs: #5 Water Heating (PDF 161 KB). (2004). Rocky Mountain Institute. 6 pp.
· Wiehagen, J.; Sikora, J. L. (March 2003). Performance Comparison of Residential Hot Water Systems (PDF 1.01 MB). NREL Report No. SR-550-32922. Golden, CO: National Renewable Energy Laboratory. 61 pp.

 

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Sizing a Demand (Tankless or Instantaneous) Water Heater
Demand (tankless or instantaneous) water heaters are rated by the maximum temperature rise possible at a given flow rate. Therefore, to size a demand water heater, you need to determine the flow rate and the temperature rise you'll need for its application (whole house or a remote application, such as just a bathroom) in your home.

First, list the number of hot water devices you expect to use at any one time. Then, add up their flow rates (gallons per minute). This is the desired flow rate you'll want for the demand water heater. For example, let's say you expect to simultaneously run a hot water faucet with a flow rate of 0.75 gallons (2.84 liters) per minute and a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute. The flow rate through the demand water heater would need to be at least 3.25 gallons (12.3 liters) per minute. To reduce flow rates, install low-flow water fixtures.

To determine temperature rise, subtract the incoming water temperature from the desired output temperature. Unless you know otherwise, assume that the incoming water temperature is 50ºF (10ºC). For most uses, you'll want your water heated to 120ºF (49ºC). In this example, you'd need a demand water heater that produces a temperature rise of 70ºF (39ºC) for most uses. For dishwashers without internal heaters and other such applications, you might want your water heated at 140ºF (60ºC). In that case, you'll need a temperature rise of 90ºF.

Most demand water heaters are rated for a variety of inlet temperatures. Typically, a 70ºF (39ºC) water temperature rise is possible at a flow rate of 5 gallons per minute through gas-fired demand water heaters and 2 gallons per minute through electric ones. Faster flow rates or cooler inlet temperatures can sometimes reduce the water temperature at the most distant faucet. Some types of tankless water heaters are thermostatically controlled; they can vary their output temperature according to the water flow rate and inlet temperature.

 

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