(360) 789-9669 codeinnovations@ecobuilding.org

Sanden CO2 Refrigerant Heat Pump Water Heater at FutureFit Home

Portland, OR, USA

Building Type




Terry Whitehill | Bureau of Development Services

Tad Everhart | owner
Maho Ito | Other
Mike Elrod | subcontractor
Jonathan Cohen | subcontractor

Residential heat pump domestic water heating systems (HPDWH) use synthetic refrigerants with high global warming potential (GWP).  In the 1990s, Japanese engineers developed an alternative HPDWH technology known as “Eco-Cute” that uses CO2 for refrigerant, a naturally occurring gas with global warming potential (GWP) 2,000 times less than synthetic. Oregon’s plumbing code requires hot water heating systems to be tested and listed by an approved agency (such as Underwriters Laboratories UL).  Although it is not yet UL listed, the City of Portland allowed us to install the CO2 HPDHW system as an alternate material through its Alternative Technology Advisory Committee process.

There were two steps in the process.  First, The ATAC heard our testimony and reviewed our evidence and recommended our technology.  Second, the building official granted our appeal and permitted us to install a Sanden Eco-Cute. The entire approval process took just over two months.  We submitted our written application and the required $150 fee to the ATAC.  Within one month ATAC held a hearing on our application and allowed our in-person testimony.  Within two weeks, ATAC informed us that it would recommend we be allowed to install our system, and it gave us a written recommendation and posted it on its website.  We then submitted our written building code appeal and the required $100 fee, and within one week, the City of Portland informed us that our appeal was granted and posted the appeal summary on its website.

Code Requirement Compliance Path
2011 ORSC section M1302.1 Requires appliances to be listed and labeled by an approved agency (e.g. UL) City of Portland building code appeal based on ATAC’s recommendation (see below); administrative ruling by City staff, followed by written, online approval.
2011 ORSC section R104.11 allows alternative materials, design and methods of construction and equipment when the material or work offered is equivalent Written application to City’s ATAC, ATAC in -person hearing, and ATAC’s written recommendation to approve..
Square Footage: 2100ft2

Even after futurefitting our home (remodeling for the future) to the super-efficient Passive House Standard in 2009, we still needed a small amount of  space heating.   And futurefitting did not change our need for domestic hot water.  An “active” heating system like HPDHW fit well with our plan: efficient, affordable, and electric to make use of renewable energy and avoid combustion of fossil fuels.  When installed, it will satisfy both our space heating and hot water needs.

The specific Eco-Cute equipment we want to install is not UL listed but it is environmentally superior, so we made an application to the City of Portland Alternative Technology Advisory Committee (ATAC).  ATAC heard remote and in-person oral testimony and reviewed written materials we submitted.  ATAC recommended approval, and the Bureau of Development Services approved our code appeal based on the ATAC’s recommendation.

In 2009, there were heat pump “combi” space and water heating systems on the market, but they were costly.  Worse, they use synthetic refrigerants with high global warming potential (GWP).  Although no one intends the refrigerants escape into the atmosphere and cause warming, some will escape notwithstanding our best efforts. Typically, refrigerants leak into the atmosphere both very slowly during normal heat pump operation and quickly either upon an accidental release (during charging or equipment damage) or at the end of the equipment’s use if the refrigerant is not carefully captured and either reused or destroyed.  There are government refrigerant capture requirements, but I am not optimistic about refrigerant capture, especially in countries with less robust environmental safeguards, regulations, and enforcement.

In the 1990s, Japanese engineers perfected high-pressure CO2 refrigerant heat pump technology (known as “Eco-Cute”).  Available in Japan since 2001, this technology has spread to Australia and Europe, but to date, it has not been available for North American homes.  Now, thanks to the City of Portland’s accessible ATAC process that approved its use for mine and also for future projects, Sanden is importing its Eco-Cute system to Portland, Oregon.

Sanden’s Eco-Cute heat pump domestic water heater combines highest-in-class heating efficiency and adequate hot water capacity even in subfreezing weather. Sanden’s system includes an 84-gallon DHW tank with sufficient heat storage for both residential hot water and space heating for high-performance homes. It’s environmentally better because it uses CO2 refrigerant instead of synthetic refrigerants which contribute to global warming if/when released into atmosphere.  CO2 has a GWP of one, far below the GWP of conventional, synthetic refrigerants (1,000 or 2,000).

We believe this technology will also help us come within the primary energy consumption limit of the Passivhaus Institut’s Passive House Standard for new buildings and EnerPHit Standard for remodeled buildings.  Also, this all-in-one electric heating system’s electrical load matches residential-size roof-top solar PV output for not just annual Net Zero Energy homes but “real-time” NZE operation.

We are working closely with our electrical and plumbing subcontractors and the manufacturer’s representatives to design and install our system.

In 2009 when we sealed and super-insulated our home, we removed our gas furnace and installed a 2.5kw electric resistance heating system within our ventilation air supply ducts.   This space heater was inexpensive, easy to install, and avoided onsite fossil fuel combustion.  There were heat pumps like mini-splits available at the time, but we did not expect to use much space heating energy.

Over the last few years, we appear to consume almost 3,000 kwh of electricity per year for space heating.  That’s more than I expected.  And it is $300/year at current prices.  This is far less than most houses, but still, we’d like to reduce our consumption further.  In our climate, Sanden’s Eco-Cute system should produce about 2.5 to 3.5 units of heat for each unit of electricity in our winter conditions. That’s far greater efficiency than our electric resistance heater which produces one unit of heat for each unit of electricity. We estimate that this technology will reduce our electrical consumption for space heating by 60%.

And it will replace our natural gas DHW system.  We already support the transition to renewable energy by participating in our utility’s 100% wind electricity purchase program.  By switching to electrical water heating, we’ll speed the transition away from fossil fuel combustion.

We hope the total cost to install a Sanden Eco-Cute HPDHW system providing both water and space heating will cost approximately $5,000 after Oregon Residential Energy Tax Credits and incentives from the Energy Trust of Oregon.  For space heating alone, the financial payback period is long (25 years) if electricity prices stay low.  At current low natural gas prices, including fuel-switching for our DHW, the financial payback period is even longer.

However, if the financial payback analysis includes the cost of global warming (accelerated by conventional refrigerants leaking into the atmosphere), Sanden’s Eco-Cute’s benefits outweigh its costs.

Tad Everhart


Maho Ito
CO2 Product Line Manager


Mike Elrod


Jonathan Cohen