Staying out of hot water with your water heater:

A Manufacturer’s Perspective on High Efficiency Water Heaters

Building America Stakeholder’s Meeting

March 17, 2011 Charles W. Adams

Types of High Efficiency Water Heaters

Condensing Gas – Tank-type – 0.77+ EF (energy factor)

– 90%+ TE (thermal efficiency)

– 100,000 Btu generates about 1 gallon of condensate

– Can be direct vent or direct exhaust

Types of High Efficiency Water Heaters

Condensing Gas – Tankless – 0.90+ EF – 90%+ TE – 100,000 Btu

generates about 1 gallon of condensate

– Can be direct vent, or outdoor (or direct exhaust – uncommon)

Types of High Efficiency Water Heaters

Condensing Gas – Hybrid – combination of a

tankless-type “heat engine”and a small(er) tank

– 0.77+ EF – 90%+ TE – 100,000 Btu generates

about 1 gallon of condensate

– Can be direct vent or direct exhaust

Types of High Efficiency Water Heaters

Electric Heat Pump – 2.0+ EF – 2.3+ COP – Pulls heat from ambient air

around unit to heat water – Most have electric

resistance back-up element

Types of High Efficiency Water Heaters

Solar Hot Water System – Consists of panels, tank

(with back-up energy source), pump station, and controller

– 2.0 - 4.0+ SEF (solar energy factor)

– Tank is essentially a modified water heater

Can be electric or gas Must be capable of supplying 100% of hot water needs

Types of High Efficiency Water Heaters

ENERGY STAR® non-condensing gas – 0.67+ EF – Two types

Power vent – Both direct vent and direct

exhaust – Dedicated vent

Atmospheric – Standard venting

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Regulatory Issues

Water heaters are covered by two different sets of Federal regulations – The National Appliance Energy Conservation Act (NAECA)

covers gas tank-type heaters at/under 75k Btu/hr input & gas tankless heaters under 200k Btu/hr (and electric heaters under 120 gallon and 12 kW)

– The Energy Policy Act (EPACT) covers gas and electric heaters above the NAECA limits

Originally intended (and defined) as NAECA = residential and EPACT = commercial (in 1987). That is no longer valid in the marketplace – there are residential tank-type heaters with inputs over 75,000 Btu/hr, andresidential tankless heaters with inputs over 199,999 Btu/hr

Installation issues that can negate efficiency, cause operational problems

Recirc loops can prevent condensing gas heaters fromactually condensing – Flue gas starts condensing at about 135 F

Condensate disposal is required – Gas condensate is mildly acidic, so drain materials can be a

concern – Some codes require neutralizers on gas condensate lines

HPWH’s have to “breathe”, so tight installations can be a problem – 1000 ft3 recommended

Venting location for direct vent units is important toprevent recirculation of flue gas into the air intake (or icing build-up on building)

Some Important “Awareness” Issues

Combi units – – As building envelopes become more efficient, the heating load

becomes less than the hot water load, so higher input high efficiency water heaters have the capability of providing both space and potable water heating.

Additional water usage by tankless at start-up – “Initiation cycle” takes 10 – 20 seconds, during which water is

flowing and not being heated to useful temperature

Heat pumps cool the indoor space around the heater – “Free cooling” in Summer, adds to heating load in Winter – There are solutions

Ducting, isolation, etc.

Contact information

Charles W. (Charlie) Adams

A.O. Smith Corporation

Corporate Technology Center 11270 West Park Place

Milwaukee, WI 53224 414.359.4274

cadams@aosmith.com