Chapter 9: Water Heating

To be used with the Guide to Building Energy Efficient Homes in Kentucky

Hot Water Use

90 gallons per day

50 gallons p

er

day

Energy Factor

Energy Factor (EF) = a measure of the overall efficiency of a water heater• Includes:

―Recovery efficiency―Standby losses―Cycling losses

Energy Conservation

Water conservation measures

=

Energy Conservation

New homes:• Keep hot water

pipe run as short as possible

• Use a manifold plumbing system

Energy Conservation

Energy Conservation

Water heater setting• Temperature = 120°F– Provides plenty of hot

water– Decreases risk of

scalding– Select dishwasher with

booster heaters

Energy Conservation

Energy Conservation

• Insulate the first four feet of all pipes• Use low-flow showerheads

Energy Conservation

• Install heat traps• Install low-flow aerators on sink and lavatory

faucets

Energy Conservation

1 quart

Every 3 months, drain ~ 1 quart

Gas Water Heaters

Energy Factors (EF) for ENERGY STAR® Gas Water Heaters

Type Energy Factor

Gas Storage (ending 8/31/2010) ≥ 0.62

Gas Storage (beginning 9/1/2010) ≥ 0.67

Whole-home Gas Tankless ≥ 0.82

Gas Condensing Storage ≥ 0.90

Gas Water Heaters

Gas water heater efficiency is affected by:• Burner design• Shape of the flue baffles• Amount of surface area between the flue gases

and the water• Presence of blowers for venting and delivery of

combustion air

Gas Water Heaters

Fuel-fired water heaters, in conditioned space:• Must be in a sealed mechanical room

―Fresh air inlets• To avoid the sealed mechanical room

―Use a fuel-fired water heater that includes provisions for outside combustion air• Direct-vent unit with a double flue pipe

Gas Water Heaters

Higher efficiency units have:• Blowers for venting and delivery of

combustion air• More sophisticated energy features

―Electronic ignition―Flue dampers―Condensing heat exchangers

• EF > 0.90

Electric Water Heaters

• Higher efficiency– EF > 0.97– Extra cost is low compared to the

savings

Electric Water Heaters

Electric hot water heaters are generally more expensive to operate than gas units.

However, as energy prices change:

Heat Recovery Units

Heat Recovery Unit = Desuperheater

• Recovers excess heat from air conditioner or heat pump to provide “free” hot water

Heat Recovery Units

In summer:– Desuperheater can

usually provide 100% of the hot water needs of a family and improve the efficiency of the air conditioner

In spring and fall:– Desuperheater is

ineffective

In winter:– Desuperheater is more

effective and saves money

Heat Recovery Units

Performance of a desuperheater is affected by:• Size and efficiency of the water heater and cooling

equipment– Cost $550 to $750– Annual savings = $50 to $180– Make sure that it does not void any mechanical

equipment warranties– Check the water supply to see if any buildup may occur

Solar Water Heaters

Images Courtesy: http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=12770

Solar Water Heaters

Cost effective option because:

• Current cost of energy• Tax incentives at state and federal levels• Can be oversized– Used to assist with heating a home

On Demand Water Heaters

On Demand Tankless Water Heater (gas)

On Demand Water Heaters

Save energy:• No storage

tank• Gas-fired units

usually heat water more efficiently than gas tank type water heaters

Summary