Category Archives: project rationales

How close to net-zero are we?

To answer this question, let’s look at the data for the solar year 2020 when our electrical use included space conditioning.

Our annual use totaled 13,428 kWh that year, while our annual production amounted to 11,390 kWh. The solar array produced enough electricity to cover 85% of our annual consumption.

To reach net-zero, we would need to be at 100% or above. So we are around 15% short of net zero and had some more homework ahead of us.

The moving goal post…

When we embarked on the project in 2009, all-electric homes were not a thing yet, heat pumps were hard to find, and solar arrays were uncommon.

At the time my focus was on using a solar hot water system to heat the building and for domestic hot water, and a photovoltaic array to cover our electrical needs. But I always found myself on thin ice when attempting to cover space heating and domestic hot water with a solar hot water system alone. In other words, getting away without a natural gas connection seemed impossible, which made the net zero goal hard to reach.

I pivoted my focus into significantly reducing the overall energy load of our building. If I had to use natural gas as an energy source, I wanted to use as little as possible. That put us on the path of our deep energy retrofit.

And it paid off.

Interim results in 2012 showed that our improvements reduced our electrical consumption by an estimated 57% and preliminary results from 2016 showed that we reduced our heating needs by an estimated 80%.

A lot has happened since 2009. Green building technologies that once were only known from excotic places like Europe or Asia suddenly made an appearance in the U.S. market, such as heat pumps. And with that, my focus on solar hot water fell away, because heat pumps emerged as a more economic option that I still could use, even if the sun was not shining.

Reducing the general electrical load of a building also has become easier since 2009 with increasingly efficient energy star appliances, LED lighting, etc.

What is standing in the way of net zero?

Yet we are not net zero, to my chagrin. What is standing in the way are two key factors:

  1. That we still rely on natural gas for cooking, domestic hot water, and occasional heating. And we still have a gas dryer.
  2. That our solar array is not large enough to cover 100% of our energy needs should we go all electric.

The second point should be reasonably easy to solve. Because we have reduced the energy load of our building significantly, we have enough room to expand our solar array to cover 100% of our energy use. And we plan on doing so – eventually – once technology catches up.

Regarding the first point – our natural gas connection – it helps to know how much natural gas goes towards what source in our building.

Analyzing our utility bills over the past seven years revealed that about 1,000 therms (77%) went towards space heating, with only 300 therms (23%) going towards domestic hot water, ranges, and the dryer.

The 300 therms seemed to be easy to solve. We can replace our gas dryer with a condensing dryer. The gas ranges can be replaced with induction stoves. And the heat pump water heater technologies have improved to the point where we could say goodbye to a gas fired water heater too.

As for the 1,000 therms going into space heating, one could argue that we solved that problem already with the addition of our minisplits. We used them to heat our building during the solar year 2020, and it worked.

But there is a problem: we drank the kool aid.

We originally, and occasionally still rely on our hydronic heating system, powered by a high efficiency boiler. The steel baseboard radiators and radiant floors deliver a comfort during the heating season that is unmatched.

The good news is that we potentially could replace our boiler with an air-to-water heat pump that used CO2 (R744) as a refrigerant. These units are slowly making an appearance in the U.S. market and are able to deliver 130F water even at very low exterior temperatures. 130F would be a suitable temperature for our hydronic heating system and domestic hot water.

Not only that, but an air-to–water heat pump would be two to three times more efficient than our high efficiency boiler. In other words, it would only require half or one third of the energy input to produce the equivalent of 1,000 therms heating output.

I am hopeful to eventually replace our boiler with an air-to-water heat pump and solve the 1,000 therms that were needed for space heating.  We subsequently could cut our natural gas supply to the building, and yet still enjoy the comfort of our hydronic heating system.

That must be expensive!

In the big picture, what is the cost of doing nothing?

And on a project basis, if it is expensive depends on one’s mindset.

Most of our system decisions, such as the heating system, were not solely based on the economics of the day, or “what is the cheapest system I can get.” We were comfortable investing in systems with a longer payback period as long as they came with:

  1. a high level of energy efficiency,
  2. some level of resiliency and longevity,
  3. improved indoor comfort and health without an energy penalty, and
  4. systems that were somewhat future-proof so that they could adapt to technology upgrades.

This required a lot of research and careful planning at the onset of our project. And it required a lot of luck, as we were gazing into the future trying to predict the path green building technologies would take.

And in practical terms?

It appears that our utility room layout could accommodate the switch from boiler to air-to-water heat pump without revamping the whole hydronic heating or domestic hot water layout.

And because we were mindful when we installed an all new electrical metallic tubing (EMT) based electrical system, providing 240V for the induction stoves and potentially the condensing dryer should just be a matter of simple rewiring.

The one item that wasn’t even remotely on the radar in 2009, and that I still have to wrap my head around, is how best to integrate and accommodate EV charging stations.

In summary: We are not net-zero yet. We are fairly close, and we know the path that will take us there.

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How do I start…

… with energy improvements on my home?

This is probably the question I get most often.

Whether you are thinking about smaller improvements or bigger ones, like our deep energy retrofit, here are some guidelines on how to go about it.

The big picture

It is not just about energy improvements, but it is also about where you get the biggest bang for your buck. So let’s take a look at the big picture.

For more data go to:

The 2015 chart above from the U.S. Energy Information Administration shows that up to 54% of energy for a single family home can go towards space conditioning (i.e. space heating and cooling). Only 5% of energy goes towards lighting.

If you decide to make your lighting more efficient, i.e. go with all Energy Star LED lighting, I applaud you. However, the total resulting energy savings may be around 1-2%. That’s something you may barely notice on your electrical bill.

If instead you would focus on improvements to your building envelope, i.e. your basement floor, foundation walls, crawlspace, exterior walls, wall penetrations, windows, exterior doors, attic, and roof, you could make a major dent in the 54% of energy that goes towards your space conditioning. This is where you can get a big bang for your buck. And not only that, you likely end up with a home that is a whole lot less drafty and a whole lot more comfortable and healthy to live in.

The bottom line is, don’t focus on the low hanging fruit. Look at the big picture and focus on the energy hogs, such as space conditioning.

Verify and quantify

You decided to not just chip away at your energy use but instead to make a dent, maybe even a really big dent.

Based on the data above, you know that you likely need to focus on your building envelope in order to reduce your space conditioning loads. But how good or bad is your building envelope, and what is the actual space conditioning load for your home?

It’s time to find out. Commission a home energy audit. A professional energy auditor will visit and inspect your home, analyze your utility bills, and may run several tests such as a duct, furnace, and blower door test.

For more information on home energy audits go to:

The energy audit report will point you to the areas where energy improvements can be most effective. The most significant recommendations will probably point you to building envelope improvements, such as insulating, air sealing, door or window replacement, etc.

With this data and recommendations in hand, you can begin to strategize.


You have a choice. Even basic insulation along with good air sealing (also called home weatherization) can save you an “average of 15% on heating and cooling costs (or an average of 11% on total energy costs)” according to Energy Star information.

For more information go to:

Depending on how handy you are, weatherization can become a DIY project or you can hire a weatherization specialist that does the air sealing and insulating for you. If you hire someone, make sure that you contractually set performance goals based on the home energy audit. This means how much more air tight the house should be after the improvements and what cold spots should be eliminated with insulation. And at the end, go and verify. In other words, have your energy auditor come back to test that the performance goals are met.

Energy model

You want to aim higher and save more? Good for you!

In this case I recommend commissioning an energy model, which your home energy auditor could provide. And if not, he or she can probably recommend someone. We commissioned an energy model in the planning phase of our project, which guided us through the decision making process.

An energy model takes a wide variety of building variables into account (type of windows, type of insulation, building exposure, air tightness, etc.) and predicts the energy load of your home. By adjusting the variables (i.e. thickness of insulation, type of windows, level of airtightness, etc.) you can see how the energy load of your home increases or decreases.

Say you want to decrease the energy load of your home by 50% or more, which puts you into the realm of deep energy retrofits. The energy model will help you to determine how to get there. It tells you what level of air tightness you need to achieve. It tells you what levels of insulation values you need, and where. It tells you what performance targets your windows and exterior doors should meet. And so on.

Decreasing your energy by 50% or more will involve major remodeling as you probably have to work on all exterior walls and the roof from the inside, the outside, or both.

Sounds daunting? Well, it can be. But there are silver linings here too.

Major remodeling allows you to get to all those quick fixes and deferred maintenance items that have been causing problems and eating money for years. And of course, you are left with major energy savings.

Take our deep energy retrofit. A preliminary analysis in 2016 showed a 80% reduction in our heating needs, and 57% reduction in our electrical use in 2012.

Be picky with your contractors

You will need help from various building trades with a deep energy retrofit. I highly recommend relying on contractors that specialize in energy improvements, or that are at least familiar with the topic. Working on energy improvements, such as in a deep energy retrofit, takes a very different mind set compared to regular construction, as the installation and construction processes often vary from the old norm. A recipe for disaster is a contractor that is set in the old ways, because that is how he/she has always done it.

Don’t tiptoe

Aiming high, such as with a deep energy retrofit, may seem expensive and overwhelming. You may think you should start in small increments instead.

Please think again.

Going about your improvements incrementally, each step in the process seems less overwhelming and less expensive. I’ll give you that. However you keep tiptoeing around big ticket items and associated savings (such as the above mentioned space conditioning). And you will likely end up undoing some of your own work along the process.

In the end, you may have spent cumulatively more on incremental improvements than on a deep energy retrofit with far less energy savings than you would have had if you didn’t tiptoe..

Learn how to operate your home

Owning a home, energy efficient or not, requires you to know how to operate it.

It is similar to owning a car: If you want to drive, you need to know how to start your car, how to steer it, how to accelerate and brake. You need to know what kind of gas you need, how to put gas in the tank, check tire pressure, check oil levels, etc.

The same is true for a home, in particular if you like to maximize your energy savings. You need to know when to change or clean which filters and when to schedule service appointments for what equipment. You will have to program and monitor your thermostat and other monitoring equipment. You should become familiar with the basics of indoor air quality (IAQ) and learn the basics about moisture management.

Owning a home is not a hands-off operation! There is no chauffeur. You need to drive if you intend to maximize your energy savings, assure the durability of your home and systems, and maintain a healthy and affordable living space.

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About gorillas and homeowners

The beauty of a project like ours is that you get to think a lot. There is a steady stream of problem solving, cascades of questions, a constant flow of ideas, and the occasional trickle of epiphanies.

One of those epiphanies emerged even before we conceived this pilot project: We can’t build our way out of a looming energy and carbon crisis with new, green and energy efficient buildings alone. They help, but the 900 pound gorilla in the room that throws a temper tantrum is our existing building stock.

According to the US Department of Energy, residential buildings consume an estimated 22% of the US energy (another 19% is consumed by commercial buildings).

We hope that this pilot project demonstrates how building owners can make a dent in that 22%. We showcase a rational process, from the big picture to the nitty gritty bits, and energy conservation strategies that should yield a good return on investment.

But I have a lingering doubt that this will be enough – because so many homeowners lack the most basic knowledge of what it takes to operate, run and maintain their buildings.

Here is what I mean: When do things get fixed? After a problem manifests through a catastrophic failure, i.e. wet drywall and mold because the parapet has been crumbling for years with rainwater infiltrating freely; or a fried furnace blower because the air filter has never been changed and is clogged solid; etc…

These things could have been prevented proactively and fixed at a fraction of the cost, if only the homeowner would have known what to look for. And it’s not only the mostly innocent ignorance of the homeowner. The various building trades are not doing that much better, but are called in to fix the problem. That’s what I call the compounding of a catastrophe.

Bottom line: We don’t invest much time into our homes any more, which is confirmed by data from the 2012 American Time Use Survey.

To effectively run and operate an energy efficient building – or any building for that matter – the owner or occupant must possess some basic knowledge about the building and its operation. Even better would be some knowledge level of building science. It could make a big difference and save big money, because it opens the door to proactivity.

It is once again nice to notice that I am not alone out there with these thoughts. Martin Holladay at picked up on the same subject and it is worthwhile reading his take in his blog “Do Homeowners Need to Understand Home Performance?

By the way, do you know what kind of heating system your home has? Forced air? Hydronic?

The green smoke screen

Why this project – why this blog?

We had to answer those questions when we developed the idea of a deep energy retrofit. The articulation of project rationales served as a foundation for what was to come.

In those project rationales, I took a stab at new, green construction, voicing our frustration that it is often unaffordable for the masses and may qualify as “green”, but misses the point of sustainability.

It turns out that I am not the only one with some level of discontent on this subject matter – and that others, such as Martin Holladay at the, are beautifully no-nonsense in their expression of that discontent.

Read his blog post –

Musing of an Energy Nerd – Who Deserves the Prize for the Greenest Home in the U.S.?

– if you like to take a look behind the “green” smoke screen of the green building industry.

As to why this project – why this blog? Martin Holladay put his finger on what motivates us, probably without even knowing about what we are up to.

Discovering the other side of green

When we went into this project we had a certain perception of green. Our goal is to eventually turn the house into a zero-energy building. We subsequently focused a lot on insulation and energy issues and associated gadgets such as solar hot water and photo voltaic.

An invaluable amount of research, a healthy learning curve and a lot of hands-on time began to morph that initial perception into something new – well, sort of new.

I had many conversations in the past with colleagues in the architectural field, colleagues that have an interest in historic preservation. When talking about green building technologies they made the case that they already were working green way before it became fashionable.

I heard what they were saying. I knew what they were saying. But I only recently got to appreciate the real depth of this statement.

Think about all the resources that went into the construction of our home in 1902, and think about the carbon foot print associated with it. The good news is that the building has lasted over 100 years already. And there is no reason why it could not last another 100, 200 or even 300 years.

This is where green begins: Spreading the energy input and carbon footprint of the initial construction thinner and thinner across the years with the increased age of the building. You can feel good about your energy efficient light bulb after you started with the preservation of and tender loving care for an old building.

The challenge

The problem is that there are a thousand very easy ways to screw up an old building, which would put a sudden stop to spreading out the initial impact.

It could be as simple as the lack of or wrong type of building maintenance. Ignoring the subtleties of moisture management and movement or the appropriate type of mortar for masonry repair work can inflict lasting and sometimes irreversible damage.

Unfortunately, the expertise on how these old buildings were put together and how they work is spread thin too. But this base knowledge is critical when it comes to retrofitting the old building stock with green building technologies.

Most of the excitement, talk and focus is on new green buildings, which does not help us with the existing building stock. I hope that the focus will shift to this sleeping giant soon, bringing back the expertise and knowledge and making it easier to access information on how to retrofit existing buildings with green technologies while preserving their integrity and longevity.