Frequently Asked Questions
Every house needs ventilation (HVAC stands for Heating, Ventilation, and Air Conditioning). The existing building codes require mechanical ventilation. They even specify the volume/speed of the ventilation system, so there is no worry here.
Building a tight house allows us to better control the ventilation air. It doesn’t get worse; it gets better! In a typical “leaky” house, air inside the house is exchanged as a result of a significant temperature difference between the inside and outside, or a strong wind. This is not ventilation: it’s called a draft. Make sure you don’t confuse the two concepts.
We prefer to use a balanced ventilation system---with heat recovery. With this type of equipment, we pull stale and moist air out of bathrooms, kitchens, and laundry rooms; we then supply fresh air to bedrooms and living spaces (places where you spend the most time). This keeps energy bills low and distributes fresh air throughout the house.
We like to use this concept: "Build tight, ventilate right."
Warning: Technical Alert! This may cause your eyes to glaze over!
Energy auditors use something called a blower door to measure the leakage rate of a building (see the picture at the top of this page). Basically, they insert a collapsible frame into an existing door opening. This frame holds a variable speed fan and some ports that are used to measure the air pressure, both inside and outside of the house.
By adjusting the fan speed, they are able to (de)pressurize the house to an industry wide standard of 50 Pascals. At that pressure, they calculate the volume of air flowing through the fan. They can then calculate the air changes per hour at the specified pressure. The result looks like this:
For our climate, the latest version of Energy Star for Homes (V3.0) requires new houses to have a maximum leakage rate of 5.0ACH50. In contrast, Passive House certification has a maximum leakage rate of <0.6ACH50 (that is 8X better than Energy Star).
At Promethean Homes, we can easily build a house to meet Energy Star standards, without any significant cost increase (it just takes knowledge of the enclosure). We can meet Passive House standards through a number of techniques. In fact, we’ll guarantee a specified leakage rate for any residential structure we design and build.
In a word, cost. The installed cost for a ground source heat pump will range from $20,000 - $40,000. In terms of efficiency (or Coefficient of Performance---COP for you nerds), we can achieve the same results with a minisplit heat pump that costs less than $3,000, installed. You save now AND later.
But that’s not the only reason. Once you minimize the heating and cooling loads of a structure, a ground source heat pump is likely overkill. We take the money that you would have spent on a fancy ground source heat pump, and invest that money in the structure (airtightness and insulation).
Some materials are just not natural. Take a window for example. You won’t find any of these in nature. And the best windows aren’t necessarily manufactured locally. Thus, we say “whenever possible.”
On the other hand, Virginia has a healthy timber industry. So do the Carolinas. We like to use Southern Yellow Pine (SYP) because it is natural, strong, durable, and beautiful. SYP is a great bioregional building material---local AND natural.
At this point, we might relate building materials to foods. When we can, we choose locally grown food. If you are a foodie, or a locavore, you probably see the value in purchasing meats and produce at the local farmers' markets. In contrast to this idea, you won't find any locally sourced coffee or halibut available in Staunton, yet, you probably still purchase these.
There are plenty of other materials just like SYP. The Shenandoah Valley has several local hardwood flooring manufacturers. Across the Blue Ridge we have a slate and soapstone quarry. Cellulose insulation is a natural material that is recycled from newsprint, and there are several suppliers in the Appalachian region.
Hopefully this helps qualify our statement.
This is a complicated subject. First of all, foam insulation does have a place in energy efficient construction. We use it when it makes sense, and use it judiciously. Otherwise, here are some points to consider as you learn more:
Spray foam insulation has its own list of pros and cons. Like any other building material, it has a place in the toolbox. If you would like to learn more about our philosophy on foam insulation, contact us for a more detailed discussion.
Simply stated, a Zero Net Energy house is defined by energy consumption and production. On an annual basis, these houses produce as much power as they consume (thus the word “net” in the name). How is that possible? Usually, these houses are equipped with a wind turbine or photovoltaic array; these devices generate power that is fed back into the electrical grid. At the end of a year, these houses have produced enough energy to balance their annual consumption.
More importantly, these houses are built in such a way that their energy needs are very low (heating, cooling, hot water, etc.). So the size and cost of the renewable energy system becomes realistic.
Zero Net Energy Ready means that at some point in the future, if you decide to add a renewable energy system, the house is built in such a way that you can expect to meet that goal with a conservatively sized system (i.e. a 6kw PV array).
There is an industry saying, “There are no Net Zero houses, only Net Zero homeowners.” And that’s true. Houses don’t use energy: people use energy. If you are in the habit of leaving lights on all of the time, or running a plasma TV twelve hours a day, you are unlikely to ever achieve Net Zero, no matter how well the house is built.
Making a decision isn’t a simple process. And it’s not always based on fact, or statistics, or reason. Much of the time emotion drives our decision making process. But this question is about money, and you want some justification, some calculations. You are really asking the question: is there a payback? what is the return on investment?
At this point, we’d like to turn the tables on you. Is there a payback on a vehicle purchase? Did you calculate the payback the last time you bought a couch? And since we’re talking about a custom house, what about granite countertops? What is their payback period?
The point we’re trying to make is this: maybe you are asking the wrong question. But we would like to answer it anyway. The payback on energy efficiency improvements can range from months, to decades. The good news is that most of the time there is a payback (unlike your couch purchase).
As an example, a heat pump water heater costs 3X - 4X more than a standard electric resistance model. But it uses less than half the energy. One study shows the payback period as 4.7 years. Since they are designed to last 10 years, this appears to be a good investment. But this study doesn’t necessarily capture the full picture. HPWHs can provide supplemental cooling and dehumidification in the summer, so some owners may choose to operate them in“heat pump only” mode for months at a time. This would reduce the payback period AND improve occupant comfort.
Other systems are more difficult to calculate. If you build an airtight and well insulated structure, the heating and cooling loads will be smaller. So you’ll spend MORE money on the structure, but you’ll spend LESS on the HVAC equipment. And your monthly energy bills will be lower. The cost parity of these improvements varies with each project.
Going Net Zero? If we assume a very low inflation rate for electricity, it may take >20 years to payback the capital costs of a whole-house PV array. But who can predict energy prices in the year 2032?
Then there is the law of diminishing returns. It’s fairly easy to cut energy requirements by 30%; it becomes more difficult and more expensive to cut those requirements by 60%. At some point, reducing the load becomes more expensive than producing electricity with a renewable energy source (this usually happens in the 60 - 70% reduction range). That’s when you stop. Or that’s when you decide to install a renewable energy system.
As you can see, this is not a simple topic!
To close this question, we would like to point out that construction costs vary wildly. If you’ve ever received bids for a job, you already know this. At Promethean Homes, we are committed to building energy efficient homes at a reasonable cost. And we have the skill set to make that happen.
We invite you to contact us for more information. We provide free consultations to those interested in learning more about energy efficient construction.
Simple. "Show me the energy bills."
Like an automobile, a house has an efficiency rating. Unlike automobiles, it isn't standardized (some houses use electricity, natural gas, and wood to supply energy needs). But a professional can boil this down to a single figure that you can use for comparison---like kilowatt hours per month. We would be glad to help with this calculation.
Or you can ask other relevent questions about their work:
Serious professionals will provide you with concise answers to these questions.
Passive House (or Passivhaus)is an energy metric that only has three requirements:
Whoa! That is way too technical! I really don’t understand what you just said!
To put this in layman’s terms, it means the house is very tight, very easy to heat / cool, and is designed to use very little energy. In fact, you could probably use a hair dryer to heat the entire house. What?! Sounds like one of those outrageous claims! You are right---it does sound outrageous---but it is a fact.
For our Passive Bauernaus, the average winter time heating load is calculated at 6,199 BTU/hr (or a half-ton when it’s just below freezing). The peak heating load is 10,404 BTU/hr (still less than a ton at our design temperature of 16°F). Since a 2,000 Watt hair-dryer produces 6,824 BTU/hr, it’s theoretically feasible to heat the Passive Bauernhaus this way.
We’ll admit that it’s a gimmick, since you would never heat your house with a hair dryer! But hopefully, you get the point. That’s a short summary of Passive House. You can read more about it here and here.
Another important point: don't confuse Passive House with passive solar. Although a Passive House may incorporate passive solar design, that's where the connection ends.
Passive House is a focused energy metric, and does not address other issues such as site / location, material selection, watershed impact, embodied energy, etc. And it's not without critics. But it does give us a great goal!