Passive house living
This post is about our experience of living in our certified Passivhaus over the first two-and-a-half years. We look at what it has been like, how the house has performed, and our energy costs. We also briefly look at the ‘extras’ of building and living in a Passivhaus and certification. We have updated aspects of this since its original posting because of the substantial increase in energy prices.
Living in a Passivhaus is simply remarkable. If you are thinking of self-building, consider building a passive house, or retrofitting an existing house to the Passivhaus EnerPHit standard, for the outstanding levels of comfort it provides, not just the energy savings.
In the Oakwrights’ video on the right we discuss our experience of living in a Passivhaus with Tim Crump, the founder of Oakwrights.
Building and living in an oak-frame Passivhaus
You can also see an update on our experience in 2022 during the July heatwave and December cold snap when our outdoor temperatures reached +34.06°C and -9.77°C, respectively.
And as well as reading this post, click on the button below to hear a more detailed discussion between us and Tim Crump in an Oakwrights podcast about building and living in our oak-frame passive house.
Thermal comfort and high indoor air quality
Our house always has a comfortable temperature: slightly warmer in summer and slightly cooler in winter. And it always feels fresh: the ventilation system, and airtightness and thermal efficiency, is like having an open window constantly providing fresh air but with no draught or perceptible air movement. (And you can open windows if you want a breeze.) In our experience, Passivhaus living means:
the house has a pervading peacefulness: a relaxing quietness and stillness;
temperatures between rooms in the house vary by no more than about 1-2°C;
there is no perceptible ‘thermal stratification’: it doesn’t feel hotter nearer the ceiling and colder nearer the floor; and although there is no heating under the kitchen floor tiles, in bare feet these always feel the same temperature as the wooden floors elsewhere, as does all the other tiled flooring even without the heating on;
there is no ‘cold radiant’ by the triple-glazed windows even when it’s very cold outside: you can sit right by the windows and admire the snow outside in complete comfort;
because of the airtightness, opening an outside door or window in winter does not create a draught or coldness elsewhere, and the temperature near the opened door/window returns to normal within moments of it being closed;
when coming in from the cold you are met by a gentle warmth seemingly coming from all surfaces, and, similarly, a gentle coolness when it’s hot outside; and
sleeping on hot, humid nights is no different to cooler ones, whereas in previous houses we’ve needed one or two fans all night. (And we use the same lightweight duvet year-round, have got rid of our electric blanket and heavy dressing gowns, and only need thick jumpers for going outside or visiting friends’ houses).
The diagram below shows the Indoor and outdoor temperatures in our house between 10 September 2020 and 9 September 2021. They were measured using high-accuracy data loggers which recorded every 30 minutes.
Indoor and outdoor temperatures between 10 September 2020 and 9 September 2021 (measured at half-hourly intervals)
You can see from the overall pattern and the average temperatures over the year, and during the coldest and the warmest months, that the indoor temperature stayed remarkably constant despite wide fluctuations outside. We only need to wear slightly warmer daytime clothing in the winter months (such as a lightweight cardigan and full-sleeved shirt) and in the summer just a tee-shirt or similar.
You can see more recent annual indoor/outdoor temperature data in this post, and details of the house’s performance during the July 2022 heatwave and the December 2022 cold snap in this post. (Outdoor temperatures at Woodlands during these two 2022 extremes reached +34.06°C and -9.77°C, respectively.)
Keeping warm
A Passivhaus is intended to have some, very limited, heating system, as described in this video. This can be almost any heating method as long as the airtightness seals aren’t breached and the heat output is appropriate. And this video shows an experiment heating a large passive house with just a hairdryer – note that it’s in America so the temperatures referred to are in Fahrenheit.
We have a ground source heat pump providing both domestic hot water and space heating although the latter rarely comes on (find out more about our Passivhaus heating system in this post).
The floor plans on the right show where our underfloor heating pipes are laid. They cover only some 25% of the treated floor area. (The ‘treated floor area’ is the usable internal floor space within the thermal envelope and excludes internal walls, doors, stairs and other ‘unusable’ spaces.)
A ground source heat pump is a very efficient way to provide heating, especially in a passive house because of the very high levels of insulation and airtightness.
And, in our experience, just having underfloor heating pipes in the hall and adjacent boot room and in each of the three bedrooms’ ensuite bathrooms is quite sufficient to boost the temperature of the whole house to a comfortable level if it’s particularly cold outside or in winter when there has been persistent cloud hiding the sun for several consecutive days.
A ground source heat pump is especially efficient because it takes free heat from the ground (which is at a remarkably stable temperature year-round) and ‘concentrates’ it to make it hotter.
The pictures on the right show, top left, that the temperature of the fluid circulating in the ground heat collector pipe entering the heat pump was 11.1ºC and, top right, the water leaving the heat pump to the underfloor heating pipes was 33.7ºC. (These were measured by fixing a thermocouple to the relevant pipes.)
The bottom two pictures show the temperature of the floor tiles in the hall and in the master bedroom ensuite bathroom (20.2ºC and 23.4ºC, respectively) when the heating was on, measured using an infrared surface temperature detector.
These temperature readings were all taken within a few minutes of each other.
In our experience, underfloor heating in a Passivhaus is an excellent choice. There are no radiators visible, which increases wall space and improves appearance, and turns the whole floor into a large radiator. Underfloor heating is ideal for a ‘low temperature’ heating system, such as a heat pump, and does not create the convection currents associated with a conventional ‘high temperature’ radiator system.
Keeping cool
As our climate progressively heats up the issue for highly insulated properties is less keeping warm in winter and more keeping cool in summer. We have not found this to be a problem. A combination of using a button on a remote control to put out blinds to restrict direct summer sunlight coming into the house and keeping windows closed when it’s hot outside, with ‘Mediterranean purging’ (opening a couple of downstairs and upstairs windows at night to flush out excess heat), keeps the indoor temperature comfortable. This is also helped by our ‘cooler battery’, described in more detail in another post.
The picture below shows the effect of the cooler battery, which itself can be seen inset bottom centre. The top left image shows that the outdoor temperature was 26°C but the air coming out of the ventilation duct in one of the rooms was just 16°C. Both of these were measured using a thermocouple; outdoors this was in still air and shade, but at the ventilation duct it was in the path of the airflow, which might have reduced its temperature reading slightly. The bottom two images show the temperatures on the outside of the air duct before and after air flowed through the cooler battery. This was measured by tucking the thermocouple under the duct’s insulation. This wouldn’t have measured the exact temperature of the air flowing within the duct but does indicate that the cooler battery extracted some 6°C from the air coming into the house (probably more, as indicated in the upper two images). All of these temperature readings were taken within a few minutes of each other.
This is not air conditioning in the conventional sense for two reasons. The first is that a passive house’s mechanical ventilation heat recovery system is a fresh air supply system, not an air recirculation one. The second is that an air conditioning system uses a refrigeration cycle and transfers heat extracted from the indoor air to the hot air outside the building, which is not an efficient way of transferring heat. In contrast, the cooler battery extracts heat by passing the incoming air over a number of fins like a car radiator with cold liquid passing inside them and transfers this excess heat to the much colder ground outside where it is stored and can be used later by the heat pump to generate domestic hot water.
Before and after views of the oak frame cleaning. Marks made in the frame milling process can be seen on the left and the pristine frame on the right
You can also see an update on our experience in 2022 during the July heatwave and December cold snap when the outdoor temperatures reached +34.06°C and -9.77°C, respectively.
Relative humidity and condensation
In common with others living in passive houses, we have had no problems with high humidity or condensation nor, in our case, with any sensation of the air being ‘dry’.
The amount of water vapour in the air depends on its temperature: warm air holds more water vapour than cold. Expressed as a percentage, the ‘relative humidity’ of air is a measure of the amount of water vapour in it at a particular temperature compared with the maximum amount of water that it can hold at that temperature and pressure. At a relative humidity of 100%, the air cannot hold any more water and if its temperature drops (say, because the air comes into contact with a cold surface like a cold window pane) water vapour will condense on it. Because surface temperatures are more or less the same everywhere in a passive house, at a comfortable level and one that’s above the ‘dew point‘ (the temperature at which water will condense from the air onto surfaces), surface condensation is not a problem.
A relative humidity in the range 40-70% is considered to have little effect on thermal comfort (above this range it becomes more difficult to control body heat by ‘insensible’ perspiration), and a range of 40-60% indoors has been identified as optimal in terms of reducing the risk of respiratory infections and allergies with the survival of airborne bacteria and viruses minimised in the range 40-70%.)
The diagram below shows the indoor relative humidity levels in our house over the same 12-month period as the temperatures shown above. This shows that for the majority of the time, relative humidity was in ‘optimal’ 40-60% range and not near the upper limit of 70% when thermal comfort would have been affected.
Indoor relative humidity (%) 10 September 2020 to 9 September 2021 (measured at half-hourly intervals by the indoor data logger)
Our high indoor air quality – even temperature, ‘healthy’ humidity and high comfort – results in there being no condensation on surfaces other than an occasional, short-lived mild misting of a bathroom mirror when showering. In all other places we have lived, condensation on indoor window panes, and mould growth in the kitchen and bathroom, have been significant issues; such condensation does not occur in our passive house.
But there is an interesting phenomenon in highly insulated buildings: on cold mornings we get condensation on the outside of some windows. Better thought of as dew, this is because triple glazing is so effective at stopping indoor heat from warming the outer pane which is thus as cold as other outdoor surfaces with dew on them.
It is noteworthy that this external dew is not present at the periphery showing that there is some heat loss through the window frame but much less through the glass itself. The thermal bridging of window frames is discussed in another post.
This picture shows the phenomenon on our north-facing kitchen window one early autumn morning.
Other descriptions of Passivhaus living
You can also find other several homeowner descriptions of British Passivhaus living on the internet (for example, some passive houses built by Green Building Store, and in Exeter), and you can read about others in chapter 13 of The Passivhaus Handbook. You can also see videos of a passive house owner in Wales describing their experience.
Passivhaus operating costs
Space heating
Note (February 2023): This section was originally written at the beginning of October 2021. Whilst energy costs have increased substantially since then the proportionate differences between our previous house and our passive house described below are probably much the same even though the actual figures would now be much higher. The heat pump electricity consumption and thus estimated annual heating costs have been updated from an earlier publication of this post (adding an additional year’s worth of data) and the calculation here is based on the median consumption (see below).
In our previous house, built in the 1970s, we had night storage heaters, a wood burning stove, and an always-on, oil-fired Aga (for both cooking and domestic hot water). Our annual energy cost (electricity, wood and oil) in 2014 was about £3,400.
Comparethemarket.com has estimated that between 2015 and 2019 domestic energy bills increased by about 40%. Ignoring energy price fluctuations in 2020 and the 12% increase in the energy price cap from October 2021, if we were still living in our last house [at the beginning of October 2021] we would probably have been paying about £4,760 per year for energy, possibly more.
The only energy we now buy is electricity and the annual cost in 2021 cost was £1,766 per year, which is some 37% of what our previous energy bill would probably have been, accounting for fuel price inflation, as described, yet our current house is bigger: approximately 200m² vs. 140m². These comparisons cover all energy use: heating, lighting, cooking, etcetera. (Our lighting is cheaper because we use LEDs.)
Both our space heating and domestic hot water are provided by a heat pump. And whilst we know its electricity consumption, because it has a separate meter, it’s difficult to determine precisely how much is used for space heating and how much for domestic hot water. However, we can try to estimate this.
The chart, below right, shows our heat pump’s electricity consumption (in kWh) from October 2019 to December 2022.
The median electricity consumption in the period was 111.77 kWh, shown on bar chart by blue dashed line. (The median is the mid-point of a range of values set out in numerical order. Using this rather than the average avoids the effect of very high or very low values skewing the average and is usually a more accurate representation).
The total of all positive differences between median and actual usage in these months, that is, the total ‘excess’ usage, was 1275.77kWh, or 79.73kWh per month for 16 of the November, December, January, February, March and Aprils shown on the bar chart where the median was exceeded.
Heat pump electricity consumption (kWh) for domestic hot water and space heating 29 October 2019 – 30 December 2022
Assumptions
We might assume that electricity usage for domestic hot water and cooking was roughly the same each month. We might also assume that in the summer less electricity was used for lighting, but some was used for running the cooler battery (which only circulates fluid to the heat pump ground array and so requires much less power than space heating), and that these equilibrate over the year and can thus be ignored. Therefore, we might consider that the above-median electricity usage in the colder months is reflects the difference between the average usage for the whole period and the ‘excess’ usage in these months and represents the use of the underfloor heating system – our only ‘active’ space heating.
Estimated heating costs
Excluding the standing charge, our electricity in December 2022 cost £0.33877/kWh.
On this basis, and averaging across some three years, our winter/spring cost of heating, at December 2022 prices, is approximately 79.73 x 6 x £0.33877 = £162.06 annually (above-median average monthly cost x months with above median electricity use x electricity charge).
Space heating a roughly 200m² house for £162 per year sounds inexpensive but it is noteworthy that the total energy consumption of our house predicted by the Passive House Planning Package at the final design stage was 98kWh per m² but our actual consumption is about 62kWh per m². Our overall energy costs are lower than predicted so this seemingly rather low estimated heating cost may not be too far off the mark. It is also comparable with the estimated cost of £90/year to heat a 200m2 passive house with a heat pump as described in a pre-energy-price-hike Homebuilding & Renovating article. This HB&R estimate was based on the heating allowed under the Passivhaus standard rather than actual measurements.
To this cost, we should add part of the electricity running cost of our mechanical ventilation heat recovery (MVHR) system because, in the colder months, it recovers heat from the outgoing air and warms the incoming air. This is discussed in greater detail in the next section.
However, the key point here is that our overall energy consumption, in a larger house, is substantially smaller than in our previous 1970s one (£1,766 vs. £4,760, accounting for fuel price inflation before the October 2021 increase) and our levels of comfort are much higher. For us, self-building a Passivhaus has definitely been worthwhile.
Other operating costs
The only operating costs of a Passivhaus that wouldn’t normally apply in a non-Passivhaus are those of the MVHR system. Ours has a maximum rating of 180 Watts. Whilst rarely run at its maximum, if it were to be throughout the year then the electricity cost, with our current tariff, would be about £530 (at our December 2022 cost of £0.33877/kWh).
But it’s important to remember the ‘HR’ part of ‘MVHR’: heat recovery. The MVHR system not only ensures high quality air and helps to prevent condensation (including protecting the building’s fabric from condensation damage), it also helps to retain a lot of heat in the house. Our Zehnder MVHR unit, which is Passivhaus Institut accredited, is rated as recovering at least 90% of the heat from the outgoing air. Generating this amount of recovered heat anew from a boiler or other heating system (which is effectively what one does in a non-Passivhaus) to make up for heat lost through draughts etcetera would certainly cost substantially more that the heat recovery component of the MVHR’s electricity costs.
The other MVHR cost is changing its filters each year. These cost about £30 + VAT for a pair (they can be gently cleaned after six months but replaced annually.)
The picture on the right shows, top left, a 6-month old MVHR inlet filter (and we live in the country, not a town) and bottom left, similarly, the filter protecting the MVHR unit from dust in the air extracted from the house. The amount of dust and debris in the air that the filters capture is shown by the contrast with an unused filter on the right and, clearly, the inlet filter makes a contribution to our high indoor air quality.
Other costs, such as annual servicing for the heat pump and the sewage treatment plant are not Passivhaus-specific and would apply to any similar property.
Running a Passivhaus
This is simple. The MVHR system automatically switches to ‘summer bypass’ mode when the weather is warmer so incoming air is not warmed by outgoing air. Similarly, when, rarely, the house gets cooler in the winter, the underfloor heating comes on automatically. And in the summer, if the indoor temperature exceeds a pre-set level the cooler battery automatically switches on to cool the incoming air.
Pressing a button boosts the MVHR if there are a lot of people in the house and another sets it to ‘unoccupied’ mode if we are away.
When it is sunny in the warmer months, pressing a button on a remote control opens both the horizontal blinds on the south-facing balconies and another opens the roof window blinds to help stop overheating. The shading effect of the balconies on the downstairs rooms, and of the balcony blinds on the upstairs ones, can be seen in the picture on the right.
And during particularly hot weather, keeping the windows shut during the day (the MVHR continues to provide the whole house with filtered, fresh air) helps to restrict heat coming in, and opening a couple of downstairs and upstairs windows in the evening helps get rid of any excess heat. This is called Mediterranean purging.
Passivhaus living problems
In our experience, there are, perhaps, two problems with Passivhaus living. The first is that it’s difficult to know what to wear if going outside without first sticking your nose out of a door or window; you feel so comfortable inside that it’s easy to think that it’s the same temperature outside too. The other problem, which is related, is that you’ll need to get rid of your winter-weight bedding and electric blanket, and those heavy jumpers (unless you are visiting someone in a non-Passivhaus) because you won’t need them again. And we’ve also given away our redundant portable heaters and fans that got so much use in our last house.
We haven’t found coping with these problems too burdensome.
Does building a Passivhaus cost more?
Based on our experience, we think the likely areas where building a Passivhaus will cost more are:
additional design work, mainly in the use of the Passive House Planning Package to ensure compliance with the Passivhaus standard (with the added advantages of being able to model the impacts of a wide variety of design and construction options and to avoid over-engineering and, subject to being constructed as designed, getting a house that will perform as intended;
possibly, some aspects of the planning process: we chose to engage a planning consultant who, together with our Passivhaus consultant at Oakwrights, created the case for our building a larger house on our plot, principally because of the thickness of the insulation, (our planning application went through without difficulty), but this is not an inevitable additional cost and planners may be more sympathetic towards proposals for a highly energy efficient house;
higher levels of insulation than in a non-Passivhaus;
triple-glazed windows: these cost quite a lot more than double-glazed ones and need much more precise installation or your money will be wasted and the house will not perform properly;
airtightness tape, which is relatively expensive and needs to be applied fastidiously, but this is an extremely small proportion of the overall cost of a building; we also had two air tightness tests where a standard build might need one or none at all (these are relatively inexpensive);
a mechanical ventilation heat recovery system: this is a key component of any property that has a very high level of airtightness;
external shading may be needed: requirements will vary with building design and site, and sufficient summer shading may be achieved simply with larger roof overhangs. In our case we had two oak-framed balconies for shading (also providing useful additional outdoor space to the upstairs master bedroom and living room) with horizontal blinds on top of these; and
the Passivhaus certification process, which is optional: we chose to do this primarily as an external quality assurance that the house had been built as designed.
The Passivhaus certification process
Passivhaus certification is not obligatory and many Passivhaus buildings are completed without it. Additional costs and work are involved in certification but the main advantage, assuming you are successful, is a formal, external assurance that your building’s design and construction were both undertaken properly. You can expect a certified Passivhaus to do exactly what it says on the tin: designing a house with the Passive House Planning Package (and then building it properly, of course), plus the verification from the formal Passivhaus certification process, takes the guesswork out of a house design from unsubstantiated claims of energy and environmental performance, and provides certainty of quantified outcomes. It’s noteworthy, for example, that the world’s first passive house, built in 1991 in Darmstadt-Kranichstein, Germany, is still performing as it was when built.
You and your Passivhaus consultant/designer will need to work with one of the small numbers of Passivhaus Institut-accredited organisations to get certification. We used a company called Warm. We took a large number of photographs at all stages of the construction, including the key Passivhaus components, to show that the materials used, and their construction, met requirements. And our Passivhaus consultant had to provide a large amount of information, as well as his Passive House Planning Package calculations. Warm then checked the accuracy of the original data and confirmed, also using the photographs and records of component specifications, their purchase and the construction, that our house had been built as intended.
Incidentally, we are delighted that two aspects of this design and external assurance process weren’t quite right: our electricity meter readings and indoor temperature records show that we are using less energy, and overheating much less, than predicted. These are nice ‘overestimates’ to have to contend with.
Is the additional cost of building a Passivhaus worth it?
In our view, quite simply, yes!
A study published in 2014 found that in most instances, a Passivhaus will have a lower whole-life cost than an equivalent traditional new build despite higher initial building costs. This was attributed to lower running and maintenance costs. That said, we think it is important to also consider the non-financial benefits of a Passivhaus:
we consider that the main advantages of living in a Passivhaus are the incredibly high levels of indoor comfort and peacefulness – this is especially important as it seems that most of us spend some 90% of our time indoors and, as we get older, this is more likely to be in our own home; and
designing our house using the Passive House Planning Package meant that we could optimise the window positions and sizes and room heights with the result that the house is flooded with natural light and has fantastic views from almost everywhere, and it feels open and airy.
And perhaps the low heating costs of a Passivhaus are worth considering in a different way. Many people throughout their working lives put money into a pension scheme. On retirement, this is commonly used to invest a relatively large sum into an annuity that will pay a regular amount of money until a person’s death. We look at the modest additional costs of building a Passivhaus in a similar way, but the ‘annuity’ we have purchased guarantees very much lower energy bills for the whole time that we will live in the house.
Would we do anything differently next time?
We enjoyed the whole process – design and building – tremendously. It was both exciting and fun. Whilst aspects of finding a plot were a bit stressful, and some of the legal shenanigans associated with its purchase we could have done without, if we weren’t so happy with the house we’ve got and where it is, we’d do it all again.
If there were a next time, we’d have better soundproofing for the plant room because the ground source heat pump is audible during the brief periods it operates, and we’d specify the use of decoupling connectors for its pipework on the walls and, perhaps, sound insulation under the floor times to reduce sound transmission. We’d also have a slightly bigger space between one of the newel posts on the stairs and a beam above it – it was too tight to get our American-style fridge upstairs and we had to bring it in over a balcony! (This was something we missed at an early discussion stage with our oak frame designer.) Otherwise, we’d change nothing.