After that quantity of water has been used then the recovery rate is all you get. The tankless or demand type of water heater must be sized according to how many gallons per minute with at least 120 degrees F output temperature. The flow rate is important too. For example: If you want the water heater to keep up with two showers being used at the same time occasionally you must calculate how much water per minute each shower uses (1.8 gallons per minute is typical). Measure the water coming out of your shower or tub spout if you must (get a 5 gallon pail and measure the time it takes to fill it up). In the case of our two shower example being taken as the most water being used then you will need a tankless heater that can deliver at least 3.6 gal./min.

Which fuel? In Louisville use gas if you have it. It is typically the least expensive fuel cost compared to electric or oil. Electric hot water costs 1.47 times natural gas (2008)
Sealed combustion chambers with power venting water heaters are typically much more efficient than atmospheric types (flue pipe goes into the chimney) (they are also safer in some circumstances). Sealed combustion means that outside air is brought in directly to the water heater and exhaust gases are vented directly outside. The combustion chamber is separated from the house air.

Power-vented equipment (but without closed combustion chamber) can use house air for combustion (single pipe flue), but flue gases are vented to the outside with the aid of a fan. In air-tight houses, drawing combustion air from the house and passively venting flue gases up the chimney can sometimes result in back-drafting of dangerous combustion gases into the house.

WATER HEATER EFFICIENCY
The energy efficiency of a storage water heater is indicated by its energy factor (EF), an overall efficiency based on the use of 64 gallons of hot water per day. The first national appliance efficiency standards for water heaters took effect in 1990. New standards, which took effect in January 2004, increased the minimum efficiency levels of water heaters. The most efficient gas-fired storage type water heaters have energy factors ranging from 0.60 to 0.65, corresponding to estimated gas use below 250 therms/year. Condensing water heaters have energy factors as high as 0.86.

Electric Water Heaters
The most efficient electric storage water heaters have energy factors ranging between 0.93 and 0.95, resulting in estimated annual energy use below 4,725 kWh/year. There is little difference between the most efficient electric resistance storage water heaters and the minimum efficiency standard. Fortunately, heat pump water heaters using less than half as much electricity as conventional electric resistance water heaters are becoming commercially available. If you use electricity for water heating, consider installing a heat pump water heater. Otherwise, look for the most efficient electric resistance unit in your size range.

TANKLESS WATER HEATERS
With demand water heaters (i.e. tankless), the manufacturers provide different specifications: the energy input (Btu/hour for gas, kilowatts [kW] for electric); the temperature rise achievable at the rated flow; the flow rate at the listed temperature rise; and so on. In comparing different models, be aware that you aren’t always looking at direct comparisons, especially with temperature rise and flow rate. For example, while one model might list the flow rate at a 100°F temperature rise, another might list the flow rate at 90°. Until there are industry-standard ratings for temperature rise and flow rates, it will be difficult to compare the performance of products from different companies without some math skills and the ability to get real data from the manufacturer. Some companies are beginning to publish energy factor ratings for these products and this information should make for easier comparisons.

COMPARING THE TRUE COSTS OF WATER HEATERS
When comparing the cost of various water heating options, keep in mind that there are two types of cost you need to look at: purchase cost and operating cost. Life-cycle costs, which take into account both the initial costs and operating costs of different water heaters, provide a much more accurate representation of the true costs of the water heater than the purchase price alone. Life-cycle costs for the most common types of water heaters under typical operating conditions are shown in the table here. When both purchase and operating costs are taken into account, one of the least expensive systems to buy (conventional electric storage) is one of the most costly to operate over a 13-year period. An electric heat pump water heater, though expensive to purchase, has a much lower cost over the long term. A solar water heating system, which costs the most to buy, has the lowest yearly operating cost among electric systems.

Contact the Water Heater Installation experts! Parker Plumbing