Vent Caps and Fan Flow

How does air move through a piece of duct? Try to imagine yourself as a molecule of air traveling through a piece of duct work with millions of your closest friends.  It might feel like driving down I-25 at rush hour through the tech-center when everyone is staying in their lanes; five lanes of traffic moving in unison in one direction basically in one straight line.  If the cars were air it would be called laminar flow; air moving smoothly though a straight piece of duct work without any obstructions, elbows, or eddies.

Now imagine an accident in the center lane of I-25.  All the cars would have to slow and go around the accident disturbing the straight stream of traffic. If it were air, or any fluid, moving around the center lane accident turbulence in the flow air would occur.  The resulting chaotic swirling lessons the amount of air that can flow through the duct just like the accident in the center lane restricts the number of cars that can pass and slows the traffic or the number of cars that can travel down the straight piece of highway.

Now imagine traveling down the 5 lane highway at rush hour and it changes from 5 lanes to two lanes to pass through a tunnel.  The flow of traffic would slow and back up cueing for its turn to pass through the tunnel as the tunnel and the restriction of lanes is a resistance to the steady flow of traffic of the five lane highway.  Sharp corners or curves in the road, passing though toll booths, and roundabouts are other examples of things that resist the flow of traffic.  In the same way airflow can be restricted.  Elbows, small diameter duct, poorly designed diffusers; all resist the flow of air in the duct and change the flow form efficient laminar flow to chaotic swirling turbulent flow. In duct work this is measured by the static pressure in the duct which is a measurement of the resistance to the flow of air, the greater the resistance the less air measured in cubic feet per minute can flow through the duct.

Now that we are measuring the flow of air through ducts on a regular basis, whether it be HVAC duct or bath fan duct, we are realizing that smooth straight properly sized duct is desired to meet the performance requirements of programs or code.  This is especially true for bath fan duct as the termination is a vent cap instead of a register cover.  It turns out that most vent caps act like the car accident in the center lane, dramatically restricting the flow air, while a duct register cover is like a car pulled over on the side of the road changing a tire, causing curiosity slowing but not impacting the flow of traffic dramatically.

As we move forward with EnergyStar V3 we are learning that the vent cap choice is as important as fan choice, duct layout, and upsizing the duct in order to ensure that fans are able to push the required amount of air out of the house.  We are building tight so we need to ensure that moisture management systems are not only installed in homes but that they are performing as they have been designed.  We know that the standard 50 CFM builder grade bath fan is not pushing nearly 50 CFM. That most often the louder the fan the less air it is actually moving. However, we were surprised when high quality Energy Star qualified fans that have been upsized in both CFM and ducting where not able to push 50 CFM.  The culprit, it turns out, is the vent cap.

Below are pictures of a very typical vent cap that we see in our market.  As you can see the screen portion surrounding the 4” diameter duct has about 1” of free space between the top of the duct and the top of the cap. The air crashes into the cap and cannot exit to the outdoors and flow through the fan is impinged increasing the static pressure or the resistance to the flow of air through the system.


Ventilation experts like Paul Raymer with Heyoka Solutions have studied the impact of different vent caps on the flow of air and more information can be found on his and others websites.  In general search of a vent cap that allows air to smoothly leave the duct on its way to the outdoors.  Just as it is difficult and dangerous to navigate a car traveling at 60 MPH around a 90° corner air can’t be expected to be able to flow smoothly into a wall (vent cap) and then exit to the outdoors.  Remember it is there and does it work – all pieces of the building science puzzle are important when it comes to performance.

Robby Schwarz
EnergyLogic, Inc.

Radon and Energy Efficiency

Why is radon a factor when addressing energy efficiency in homes?

Your home is a system comprised of multiple components working together to provide shelter and a healthy indoor environment. Radon is an invisible, odorless radioactive gas found in soil and rock that can seep into your home through gaps in concrete or bare soil commonly seen in homes with crawl spaces. High levels of radon gas in your home can be caused by many factors. A “tight” home is desirable for energy efficiency. However, radon and other pollutants can be trapped in a more air tight home. On the other hand, a typical “leaky” home can have elevated radon levels due to the stack effect. This is a condition caused by air leaks at the top of a home which create a vacuum and pull soil gasses from under your home. Fort Collins has been identified as an area with the highest potential for elevated radon levels. For this reason, EnergyLogic and the City of Fort Collins recommends that radon levels be checked before and after any energy efficiency improvement which impacts the air boundary of your home. Low cost radon test kits are available through the City of Fort Collins.

How to mitigate radon and make a home more energy efficient.

The first step in controlling indoor air pollution is to eliminate the pollutant source. Sealing air pathways between soil and your home will eliminate the source of radon and other indoor air pollutants in soil including mold and dust while improving energy efficiency. Homes with basements typically have concrete floors. Concrete is an excellent air barrier so sealing cracks in concrete floors and foundation walls can be very effective in reducing radon levels. Homes with crawl spaces often have no air barrier over bare soil or a plastic air barrier that is not sealed around the edges. Plastic that is not sealed is ineffective as an air barrier. A sealed polyethylene air barrier can be installed on the ground in most crawl spaces at minimal cost. To ensure success in reducing radon levels a passive radon system should be installed to allow radon below the barrier to vent outside the home. Passive radon systems should be designed so that a fan can be added later if necessary to create a vacuum, pulling radon gas out from under your home. When choosing a radon fan it is wise to choose the lowest wattage fan that will reduce radon levels in your home. Radon fans can operate on as little as 15 watts or over 160 watts. Often radon fan wattage is ignored or downplayed with comments like, “It only uses 60 watts, just like a light bulb. Don’t worry about it.” The point that is missing from this statement is that light bulbs are typically on for two hours a day or less. Radon fans run continuously. A 60 watt radon fan running continuously will consume 526 kWh of electricity in one year. A 60 watt light bulb used for four hours a day will consume 88 kWh of electricity in one year.

Radon is one indoor air pollutant that can easily be eliminated from your home with careful planning and air control.

I Love KPI… It’s a Radio Station, Right?

KPI is the latest buzzword here at EnergyLogic.  Though it is not a new idea, it’s one we are finally embracing on a strategic business level.  Our controller Janet Howard was asked to layout the definition of KPI, and how EnergyLogic will track them. We thought it would be helpful for some of our partners out there to review as well.

What is a KPI?

KPI stands for ‘Key Performance Indicator.’ A “KPI” is a form of performance measurement that helps to evaluate a company’s success in tangible and intangible ways – financially, strategically, internally (employee satisfaction, retention, etc.), or externally (e.g. sales, lead conversion, time to sale, etc.).  A company’s type of business and specific objectives normally determine what indicators are appropriate to track for that particular company.

Why should I care about these?

As an employer and an employee, we should care that we make or beat our goals because they affect our ability to attract and retain good people, to price our services correctly, to attract new business, to grow our business, to create value in our business, and to invest in new areas.  All of these things ultimately allow us to broaden the types of career positions we have to offer our employees, which will result in higher wages and greater responsibility for those who work for it.  This requires a longer view than just saving money or providing good customer support.  It takes an observant eye for trends and an attitude toward investing in your future.

In EnergyLogic, we track the following indicators on a rolling 12 month basis each month:



 Profitability Operating Net Profit Margin(Net Income/Revenue) This tells us what our net profit is in % form, after operating expenses and cost of goods are deducted from the revenue.  We set our profit goal during the budget process each year.
  Billing Rate Efficiency(Revenue/Payroll Cost) The higher this rate is, the more profitable we become.   This number (expressed as a multiplier, like 2.5 or 3.2) is very sensitive to shifts in total payroll.  This goal will vary rather widely between companies, depending upon what their payroll costs are and how much profit they want to realize.   Large companies with a lot of admin infrastructure must set their goals much higher, just to cover expenses.
Liquidity Current Ratio(Current Assets/Current Liabilities) This shows if we have enough capital to meet short term obligations.  This should be at least 2.0 or higher, meaning we have enough assets to cover all of our short term liabilities like lines of credit and payroll and credit card liabilities, not counting long term debt.
  Debt Ratio(Total Debt/Total Assets) This shows total debt in comparison to our total assets.  A ratio of 1.0 would mean that our debt is equal to our assets, which is not ideal.  Banks prefer this number to be less than .78
Operating Receivable Turnover Ratio(Net sales collection (cash basis)/Average AR in the same period Companies generally will have a goal of 30 days to collect their invoices.  Some give 45 days or longer, to accommodate some of their larger clients which tend to take longer to get invoices through their AP systems. This takes constant vigilance though.  If this is consistently turned over, a company should maintain a positive cash flow.
  Debt Coverage Ratio(Net Income (cash)/Loan and Lease Payments This is a little different than the Current Ratio above.  This must be at least 1.0 which would mean that we have enough cash income to cover all short term and long term debt monthly payments.
Solvency Leverage Ratio(Long Term Liabilities/Shareholder Equity) This shows how much long term debt we have in comparison to owner equity in the company.  Banks generally want this number to be less than .7 to maintain current lines or obtain new ones.
Growth Compound Annual Growth Rate This % is a complex formula applied to a factor (like revenue or net income) over a specific period of time.  It smooths out the highs and lows and produces an average rate of growth over that time period.  20% or higher is considered a very good rate.
HR Attrition Rate(# Terminations/Average Annual Headcount) This % is very sensitive to terminations in any form.  It could be a factor to watch for with some companies, as it may indicate issues with dissatisfaction or management within the company, which could affect sales and customer satisfaction.  In some companies, this rate is expected to be higher or lower in certain periods of an employee’s career, and is managed to a specific goal in those periods.

There are hundreds of KPI’s that could be tracked, and we always look for indicators that would be useful for our company to understand, but let’s face it, you are the people in the trenches every day.  You see things that management cannot always see – things that we should be doing or tracking, and things that we may be looking at that simply don’t matter.  They could be tangible or intangible.  When the light bulb goes on, don’t be afraid to step forward with your ideas. You may lead all of us to a much better place for doing so.

Janet Howard
EnergyLogic, Inc.

Janet Howard is EnergyLogic’s Corporate Controller, and has been working with EnergyLogic since 2009.  Janet formerly worked for Arthur Andersen’s Consulting Division’s Budget and Strategic Planning group that reported to the CFO of Andersen Consulting (which became Accenture, Inc.).