You are here: Home Making it Easier to Build Green! Case Studies Undersized heating system at North Passive House

Undersized heating system at North Passive House

Case Study by Nathaniel Kinne
Enter a keyword to search for code innovations.

Browse all case studies

Undersized heating system at North Passive House
Heating, Ventilation & AC
Heating and Cooling
Passive House Design, Heat Recovery Ventilation
Tom Hill, City of Olympia
North Family
The Artisans Group
The Artisans Group
Level 5 Built Green Certified Passive House


Because of a super-insulated, high performance "Passive House" design, a central heating system was not required to meet heat load requirements.  The building official allowed a smaller-than-standard heading system, a Navien combi-heater: a high efficiency, tankless, natural gas powered water heater that delivers heated hydronic fluid to a fluid-to-air heat exchanger installed in ductwork for the home's ventilation system.  Energy efficiency, building science and technology make a house that is extremely airtight and insulated.

Approval Process

The project’s uniqueness challenged the building official to find a way to permit a smaller-than-standard heating system while still adhering to all building code regulations and generally assumed rules.

The building official used the authority found in WA State Administrative Code Section 103 – Alternate Materials. The heating system was permitted with a caveat that the home’s heat load be monitored over the pilot year, and, in the case of sub-standard heating, a prescriptive heating system be installed. The structure also had to meet all Washington State Energy Code Heat Load requirements.

Code RequirementCompliance Path
Washington State Mechanical Code WAC 51-11-0503 To comply with WA Admin Code Section 103 – Alternate Materials, project had to meet all Washington State Energy Code Heat Load requirements, and home’s heat load had to be monitored over the pilot year

Project Description

The Building Official, Tom Hill, permitted the use of this heating system based on the information provided by the Artisans Group and the Passive House Planning Package. This energy model calculates the house’s heating load before it is built, and it is with these numbers that the heating system was shown to be entirely capable. However, because this project was the first iteration of a Passive House Design in Thurston County, the permitting officials only agreed to sign off on the project if space was left for a much larger heating system that could be installed during the first trial year of occupation if the smaller heat system failed.

The heating system is a Navien combi-heater. This is a high efficiency, tankless, natural gas powered water heater that has two hot water delivery circuits. The primary circuit delivers heated hydronic fluid to a fluid-to-air heat exchanger that is installed in the ducting for the home's Heat Recovery Ventilation system. The other circuit in the water heater delivers domestic hot water. The calculated heat load for this home is 5,890 btu, max load per hour. Please see the attached load report from the PHPP. Washington State University Extension Energy Program monitors the house’s energy usage. Through meticulous energy modeling, this home will save about 90% on heating costs compared to a typical home.

Project Specs:

  • Wall Insulation: R 50
  • Roof Insulation: R 81
  • Floor Insulation: R 63
  • Windows: Thermotech, U value .16, (R 6+)
  • Air tighness: Extreme (.38ACH @ 50 pascals)
  • Energy Recovery Ventilator (fresh air system)
  • Heat Source: Space heat and Domestic Hot water both run off a 98% efficient tankless water heater
  • Lighting: LED
  • Appliances: Energy Star


Resources and References:

The Artisans Group Page
A look at the North House
Passive House Institute of the US


Project Contacts
Builder: Randy Foster, Principal Artisans Group (360) 570-0626 Owner: Tom Hill, Building Official City of Olympia (360) 753-8486 Owner: DT and Kimberly North
Document Actions
  • Print this Print this