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Living in a Passivhaus

We’ve enjoyed comfortable interior temperatures and relative humidity, plenty of fresh air, and very low energy bills

Posted on Oct 14 2014 by Daniel Roy

[Editor's note: Daniel Roy is one of the owners of a recently completed Passivhaus in Falmouth, Massachusetts. Designed by architect Steve Baczek, the house was featured in a series of GBA videos. For more information on the home's energy specifications, see the attached Excel spreadsheet.]

We moved in to our new house on New Year's Day 2014. We have found that living in a Passivhaus is fantastic, and the house performs as expected.

During our first winter, we experienced one of the most severe tests we will ever face in our Passivhaus. The cold “polar vortex” winter of 2014 was one of the toughest winters in many years. In spite of this, the house remained very comfortable.

On sunny days, the minsiplit heat pump stayed off

To us, comfortable meant temperatures from about 65°F to 70°F, relative humidity of about 40%, and of course no drafts. We found ourselves rarely using the backup minisplit heat pump. If the sun was shining during the day, the sun and internal heat sources (people, dogs, appliances, etc.) in the house were sufficient for us to remain comfortable all day and night, and we didn't need to turn on the backup heat. Indeed, for our preference, we would have preferred a somewhat colder bedroom for nighttime sleeping.

If the day was cloudy, we turned on the heat pump, usually for an hour or two. We found that once the heat was inside the house, it wasn't going anywhere very quickly. We found ourselves using the heat pump maybe once a week. Admittedly, we had some extra heating assistance from our other heat source, our 8-year-old plasma TV, which cranks out a warming 500 watts when we watch it in the evening. We have since replaced the TV with an LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. unit that consumes only 120 watts.

Energy-stingy ways to stay cool

During the spring, we kept the windows closed most of the time to keep out the pollen and relied on the inlet air filtration of our ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.. Our ERVEnergy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV. is equipped with a pre-cooling ground loop, and that system was usually sufficient to keep the house comfortable.

This summer, we experienced what it was like living in a coastal humid climate. With outdoor relative humidities consistently at 80% or higher, we wanted to keep the house at about 55% RH. We did this by running the heat pump in either AC ("cool") or dehumidification ("dry") mode through most of July and August. Our ceiling fans are equipped with high-efficiency DC motors, and we ran these fans much of the time. These methods kept the house very comfortable (75° to 78°F). In spite of this, our monthly electric bills went up by only about 100 kWh (or $20, based on our electricity cost of 20 cents per kWh here on the Cape).

During the fall, we typically open two or three windows on both the first and second floors to allow for natural stack-effect cooling, provided the humidity is low.

Fresh ventilation air

We love the idea of living in a house that has no combustion and 24/7 ventilation. This keeps the air fresh and filtered (when we keep the windows closed).

Everything in the house is electric, including the heat-pump water heaterAn appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed. , the induction cooktop, the clothes dryer, and the backup heating and cooling systems. With the house so tight and insulated, we have found the interior to be very quiet. Only our dogs seem to be able to detect the faint barking sounds out there.

The wi-fi signal was blocked

One disadvantage of a tight house is that wi-fi signals are unable to penetrate the walls, just like the heat energy. Future Passivhaus buildings should have exterior Ethernet connections so that people on decks and patios can be online.

Another product which could use improvement is the condensing clothes dryer — a dryer does not exhaust to the outside. It is small and inefficient to run. With a Passivhaus, there is no simple non-mechanical way to use exterior exhausting products like conventional clothes dryers and range hoods. Even when we run our 120-cfm central vacuum cleaner, it is pulling a vacuum on the inside of the house. If we leave a window cracked, the vacuum airflow will pull it open. The reason is that there is no easy way to get the high air flows needed for these devices, unlike in a conventional house where the extra air is supplied by leakage through cracks and crevices in the house.

On track to be net-zero

We are on track to use about 7,200 kWh per year for our all-electric house. This is the same number of kWh we used in our previous conventional house, but at that house everything was gas (heat, hot water, clothes dryer, and cooking). The new photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system that we installed will generate about 10,000 kWh annually, enough to also power a future electric car and still have our new home be net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations.. I should get about 10,000 miles with the 2,500 excess kWh that my PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system provides.

Dan Roy is a Certified Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Consultant (CPHC) with PHIUS and a licensed professional engineer (mechanical) in Massachusetts. He worked many years in various engineering jobs, but this is his first Passive House design. Dan wanted to live in his first design so that he could experience it firsthand and share what it is like living in a Passive House.

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Image Credits:

  1. Image #1: Dan Roy
  2. Images #2 and #3: David Fell Photography

Oct 14, 2014 3:47 PM ET

Make Up Air for Range Hood and Dryers
by rjp :

Make-up air for range hoods and dryers is a big issue for all residential construction. Obviously the installed ERV is not capable of supplying adequate air volumes for range hoods and dryers. I wonder why passive home designs can't employ commercial style make up air for range hoods and dryers? Perhaps laundry rooms need to be sealed from the rest of the house to allow it's own makeup air. It would seem dryers could be designed with intake as well as exhaust air vents making that problem much easier to deal with.

Oct 14, 2014 4:41 PM ET

make up air
by stephen sheehy

For our new house, we're thinking about a heat pump dryer and a recirculating hood to avoid the make up air problem.
The development of a ventless wood stove is on the same schedule as fusion power, so I guess we'll need a source of make-up air for it.

Oct 14, 2014 5:19 PM ET

condensing dryer
by Jeff Stern

We've owned an Asko condensing dryer for more than a year. We were prepared for some compromise in drying performance, but we have been pleasantly surprised by it's performance. I would not hesitate to recommend it.

Although less convenient, locating the dryer outside of the thermal / air-tight envelope is another common strategy to allow use of a traditional venting type.

Oct 18, 2014 12:02 PM ET

Straube testing something nothing at all like David's
by aj builder, Upstate NY Zone 6a

Just looked at the Straube wall attachment details. 6 mil interior poly, wall had water leaks. End of story folks!!!!

Take a sandwich bag put a tiny hole in it, hit the surface with rain, then call me when the inside of the bag drys out. Never. End of story.

Martin, you and many of us... know interior 6 mil poly is asking for trouble, and it has been noted thousands of tract built homes will have a flashing leak or two or more... from day one or soon after...

Straube and company do a lot of research to aid tract builders. Great work. I love the work. But lets all talk about apples and apples... or oranges and oranges.

No one should ever build the wall that Straube posted where I live, ever.

Oct 18, 2014 12:07 PM ET

Follow the money
by aj builder, Upstate NY Zone 6a

Owens Corning, Georgia Pacific or little Cellulose manufacturers....

Done, I rest my case, rebuttals welcome.

Why aren't more homes sheathed in exterior drywall???? Gotta be something to do with the money trail in what we builders are marketed to use.... Martin? Dana?

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