RESIDENTIAL WATER HEATING

For 20 years Liquid Solar has been designing & installing innovative/efficient residential water heating systems.

CHOOSING AN EFFICIENT WATER HEATER

Often, when plumbers are replacing existing water heaters on older homes they will recommend the least efficient, lowest cost water heaters.   Many builders and architects will do the same thing on new homes.

Below are some recommendations for higher quality and very efficient alternatives.

Note: summaries of pro/cons for our recommended water heaters can be found at bottom of page.

1. NEW CONSTRUCTION/NEW BUILDINGS

When designing a new home there are generally fewer constraints and thus more options. Some general recommendations:

  • The amazing efficiency of a heat pump water heater is hard to beat. Especially if the house is all-electric. Often makes sense even if house has natural gas or propane.

  • If house has solar PV or is all-electric, Marathon electric water heaters are long-lasting well insulated tanks that are an alternative to heat pump water heaters.

  •  If natural gas/propane is preferred, then a gas tankless water heater is the most efficient. If a high efficiency gas boiler for hydronic heating is being installed, a tank water heater (often called a water-maker or indirect tank) tied to boiler is a decent choice.

  • An electric tankless water heater is a good choice if mechanical area space is limited; if usage and occupancy is intermittent; or the load/demand is small (e.g. an ADU).

  • If home will have intermittent periods of high demand but maximum efficiency is desired, then a combination system with a heat pump water heater and a booster (e.g. tankless electric or gas) for periods of high demand works well.

  • A solar hot water system can be great if demand is high, or if a heat pump water heaters or solar electric do not make sense.

2. EXISTING HOMES/BUILDINGS

On existing homes there are a lot factors at play in determining good efficient options, including (but not limited to): cost, local availability, performance, space/sizing, reliability, and fuel type.

Click on the table below to identify your existing water heater (fuel & tank type); then it easier to determine the best efficiency upgrade.

Note that it is best to replace an old water heater before it fails so that more options can be considered!

WATER HEATER COMPARISON CHART - CLICK IMAGE TO ENLARGE

EFFICIENT RESIDENTIAL WATER HEATERS

Heat Pump Water Heater

The most efficient water heater.

  • Pros

    • Uses 75% less energy than an electric water heater and 85% less than a gas water heater

    • Reliable, proven technology

    • Available in 50, 65 and 80 gallon sizes

    • Very D-I-Y friendly

    • May qualify for federal tax credits. City of Bozeman offers $500 tax credit.

    • Stiebel brand (our preferred) only requires 15 amp breaker; others 30 amps.

    Cons

    • Not a good choice in small closet or small space (need at least 50-100 square feet; unless ducted).

    • Not recommended for high hot water demand (although increasing storage volume/# tanks may work).

    • Older model were noisy; new ones much better (the new Rheem is only as 48 decibels).

    • Some plumbers will claim “they don’t work” (wrong) and will not want to install.

    • They are taller than a standard electric water heater of the same tank volume.

    • Installed cost: $2,500 to $4,000+ (not including tax credits). DIY source from Lowes for $1,500+

    • Preferred brand: Steibel-Eltron Accelera series; Bradford White  Aerotherm series are our current preferred. But all brands are constantly improving.

    • Other brands like AO Smith, LG, Rheem seem good too.

Electric Tank + Solar PV

If adding solar PV to an existing home that already has a electric water heater

  • Pros

    • Basic electric water heaters are low cost and >95% efficient.

    • Add enough solar PV to cover usage of water heater and eliminate water heating costs.

    Cons

    • Uses 3-4 times as much energy as a heat pump water heater.

    • Standard 50-gallon electric tank is $500 (not including install) (30 amp breaker)

    • A MUCH better electric tank is the Marathon (by Rheem): they are non- metallic (will never corrode) and very well insulated: $1500 for a 50g and they have a “stubby” (low and wide) shown in pic above.

On-Demand (Tankless) Gas

The most efficient gas water heater if the high efficiency versions is chosen.

  • Pros

    • High hot water production if sized properly.

    • Efficient: 80% to 95% (depending on model chosen).

    • No standby energy loss from a tank.

    • Compact

    • Reliable and proven.

    • Many plumbers will install.

    Cons

    • Requires venting and gas lines (unlike electric)

    • If hard water requires annual maintenance or hard water treatment system.

    • Rinnai and Navian are two of the best brands. Rheem is good too.

    • The lowest cost ($800 online) are “non-condensing” and 80% efficient.

    • Condensing models cost >$1200 and are 95% efficient.

    • An installed high efficiency tankless may be $3k to $4k.

On-Demand (Tankless) Electric Water Heaters

The most compact water heaters. Recommended for new construction and retrofits. Rock solid.

  • Pros 

    • Very efficient (no storage of hot water)

    • Very compact

    • Can satisfy very high hot water demand situations if sized properly

    • Durable and long lasting if properly maintained (hard water is the concern)

    • D-I-Y friendly

    • Low unit cost (but need to consider electrical costs)

    Cons

    • Not good where water is very hard (or requires water softeners)

    • Some plumbers will claim “they don’t last” (we tend to disagree”)

    • Larger ones have high amperage requirements

    • Unit cost $450 to $800 (size dependent); Installed 2x that but depends on wiring costs.

    • Steibel-Eltron Tempra series (many sizes); also Bosch, Eco-Smart and Rheem.

    • Available on-line only or we can supply.

Wall Mounted Compact Tank Style Water Heaters (electric)

Very common in Europe where they will put several in a house and close to each point-of-use. But can be used as whole-house water heater where demand is low, or as a backup where water is pre-heated by solar or by an A2W heat pump. 

  • Pros 

    • Space efficient; 20 or 30 gallon tanks.

    • Wall-mounted; high on wall so they do not occupy floor space; connections are on bottom of water heater.

    • Only requires 15 amp breaker.

    • Easy to adjust dial for water temp from 80F (vacation mode) to 160F (so smaller tank has more capacity).

    Cons

    • Slow recovery rate once hot water is used up  (but still fine for small homes).

    • Most plumbers don’t know about them and not available locally.

    • Unit cost: $600

    • The only company that brings these in from Europe is Stiebel-Eltron 

    • PSH20 Plus is 20 gallons and the PSH30 Plus is 30 gallons.  

    • We can supply. Or online.

Solar Hot Water (a.k.a solar thermal or solar heating)

Versatile, work-horse of water heating that we love in the right situation.

  • Pros

    • High hot water production.

    • Can meet up to 70% of annual hot water demand.

    • Not net metered or tied to utility grid; not subject to utility monitoring! 

    • Reliable and long-lasting if well designed and installed.  

    • Great for off-grid homes.

    Cons

    • Requires some type of backup water heaters for cloudy days.

    • Installers hard to find (but can be D-I-Y friendly).

    • Installed: $6,000 to $10,000 + ; DIY: $2,500 to $5,000 +

    • We are dealers for Sun Earth and we believe they make the solar collectors, racking, and an excellent app-based solar control

    • We source Stiebel Eltron tanks as we have found they are long lasting, affordable, and well insulated