Banish Payback

green_house-300x300Every conversation about zero energy homes (ZEHs) eventually comes around to the question of “cost.” The negative connotation of added cost and, even worse, “payback” always puts ZEH advocates at a disadvantage. For years, I’ve encouraged advocates to call energy expenditures investments rather than “costs that must be recovered”.  So, let’s banish the entire idea of “payback” and “payback period.”

Would anyone judge a stock investment or an interest bearing bank account by calculating how long it would take the earnings to equal the principal? No, that would be absurd. Likewise, it’s counter-productive to consider funds used for energy improvements to be costs. They are investments with a financial return that is both significant and predictable – both immediate and long-term.


Which of these two houses cost more overall?

When you spend money to reduce energy use, you receive a tangible financial benefit that begins the first month and continues for as long as you own your home. Let’s say that you’re building a new zero energy home. You can calculate how much it will cost to increase insulation, reduce air leakage, improve equipment efficiency and add photovoltaic panels. In most cases the investment will be in the tens of thousands. This investment will return immediate benefits whether you finance the purchase or pay with cash.

To illustrate the idea, let’s use an example of an investment of $40,000 in energy efficiency measures needed to bring a new house to zero energy. In my area, financial incentives from the electric utility, state and federal government cover just under half and reduce the amount to $21,000.  If you finance this home with a conventional 30-year mortgage,  with current mortgage interest rates at 4%, you’ll pay $50 per month for each $10,000 you add to your principal amount. Let’s assume that you financed the additional construction cost of $21,000 (after incentives), then your monthly added payment for energy improvements  would be $100.  Based on energy modeling, let’s, assume that the home will save $200 per month for energy.


That $200 return starts the first month you live in your house,  and in this example, it exceeds the added monthly mortgage payment whether incentives were used or not.

Financing Summary Additional Investment Monthly Payment (30 yrs at 4% ) Monthly Energy Savings Net Return
With Incentives $21,000 $100 $200 $100
Without Incentives $40,000 $192 $200 $8

You can also turn this calculation around by first looking at savings and then calculating how much money you could afford to invest. By building a home that saves $200 per month, you could afford to invest $40,000 in energy improvements.

In return for your investment, you pay nothing or very little for energy from the day you walk in the door. The monthly savings almost always offset the additional mortgage payment. Many cost-effectively built zero energy homes will realize a profit on their investment during the very first month, as in this example. It’s a very simple idea. If the monthly energy savings exceed the monthly financing cost, you win!

— Bruce Sullivan, BASE zero, LLC,

– See more at: Zero Energy Project

Simple, Effective, Affordable Indoor Ventilation

IMG_17931-241x300We recently received this question from Keith in San Diego. I’m a regular volunteer for Habitat for Humanity, and I’ve got a question for you. How do we get variable amounts of tempered, filtered make-up air back into our houses? As you know, we’re building houses tighter than ever, and our affiliate is using 1 inch EPS foam on the outside of the house as well. ASHRAE 62.2 is great at calculating what to exhaust to meet their standards, but in a really tight house, you need something to exhaust.  An HRV would be a bit much. My question is – how do we meet the requirements in a logical and cost-efficient manner?

Many authorities require that automatic ventilation be provided in homes where the tested air leakage rate is below 7 air changes per hour at 50 Pascals (ACH50). It’s likely that the homes you’re building with Habitat for Humanity are at or below that threshold. Providing ventilation that is effective and also inexpensive can be quite a trick. Such a system must expel the odors, moisture and pollutants from the living space and replace that same amount of air from the outside. Your question concerns the replacement or make-up air.

Automatic ventilation is an essential element of high-performance homes. In leaky houses, this make-up air comes through openings in the building envelope — we call these drafts. By sealing the drafts, we can make the home more comfortable and energy efficient. But how does the make up air enter? Vents built into window frames or installed through walls are often used. They are inexpensive, but they are little better than the leaks they replace.

A better approach is to direct the make up air to specific locations in a building to complement locations where air has been expelled. Let’s call these locations supply points and exhaust points. You could use one fan to exhaust air and another fan to supply air. This is a “balanced system” and it has the advantage of delivering outside air to specific locations. Generally, you would want to exhaust air from bathrooms, laundry rooms and other wet locations. Supply air can be delivered to bedrooms. The combination of exhaust and supply flows balances the air pressure and mixes outside air throughout the home.

Balanced flow can be accomplished by a heat recovery ventilator or energy recovery ventilator. (For convenience, let’s call them both HRVs.) Inside an HRV cabinet there are two fans, one to exhaust stale air and another to supply outside air. With an HRV you get one package that serves both purposes. (Plus heat recovery, but let’s put that aside for now.) One HRV can provide whole house ventilation that meets the ASHRAE 62.2 requirement. Most equipment can operate at several speeds. In addition to whole house ventilation, an HRV can also provide spot ventilation for bathrooms. A simple 30-minute timer in each bathroom can boost the fan speed  to high when more ventilation is needed.

HRVs are not cheap. Equipment and materials alone can cost $1500 – $2000. But then high-quality bath fans can cost $200-300 when installed in new construction by a licensed electrician. If the HRV replaces two bath fans, that can offset some of the cost. While installing HRVs requires a certain level of knowledge and skill, I think Habitat volunteers could do a good job with proper training.

Nevertheless, it’s probably difficult for most Habitat organizations to justify the cost of HRVs. Here are two alternate ideas. First, you can install a balanced ventilation system without the heat recovery function. It’s cheaper and easier to install. Two in-line fans attached to a branched duct system can provide excellent ventilation for about the same price as a two, high-quality bath fans, and without the aggravation of passive vents in walls or window frames. Two manufacturers (Broan and Fantech) make a single unit that contains two fans for a balanced system.

Second, you could install a  Panasonic WhisperComfort Spot ERV for about $350 each.  A single unit installed in a central location would provide general ventilation for the whole house, while bath fans would cover spot ventilation. Another option would be to install one WhisperComfort unit in each bathroom, replacing the bath fans.

Both these solutions offer balanced ventilation to maintain good indoor air quality, but would be far less expensive than a HRV.

— Bruce Sullivan, BASE zero, LLC,

– See more at: Zero Energy Project