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What Is This CFM Thing, And Why Do I Care?

On July 8, 2010, in did you know, by jake
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In this industry, CFM ratings are the “horsepower”, so to speak, that people use to compare products.

This statistic is used to measure how much air a fan can actually move. Here is the tricky part…Static Pressure. This is the number you see, usually measured in inches of water column, on those charts that show CFM for a given fan. Fine, what is it then?

In a word, resistance. That is, how much duct does the fan have to push or pull through? How many bends in the run? These are factors that can increase the Static Pressure and decrease the performance of the fan.

When fan shopping, be sure to compare apples to apples as some Manufacturers provide CFM at 0″ SP, while others may show what the fan could do under more adverse conditions such as .2″ or more. Which is more likely how it will perform when installed.

Here is a sample chart to let you see how things can change…

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A Little About Air…

On July 8, 2010, in did you know, by jake
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We believe that a well informed customer will always have a more gratifying experience. So in that regard, here is the 10 minute ‘expert’ course in airflow. What we won’t discuss for now are the human engineering aspects. Thermal comfort is a complex science.

What is CFM?

You see the numbers everywhere, what does it mean? CFM stands for cubic foot per minute. This term is used as a measurement of airflow rate for ventilation systems. The cubic foot refers to a cube of air 1 foot x 1 foot x 1 foot. CFM represents a volume flow rate, since we measure how many cubic feet are flowing by per minute.

Air is really, really light.

It takes 13.5 cubic feet (101 gallons) of air to weigh 1 pound. For a 2,000 square foot house, that means all the air in that house weighs 1,185 pounds – not much. Warming or cooling air is “low calorie”. To warm all that air in your house up from 50 degrees F to 70 degrees F takes about 5,688 BTU’s. The smallest house furnace puts out 40,000 BTU’s per hour. So how come it takes so long to heat up the house on a cold morning? (hint: you’re not just warming the air) An unsealed door jamb, leaking 50 CFM, would over the course of 24 hours, leak out 72,000 cubic feet of air – not “low calorie.”

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Hole in one.

On July 1, 2010, in technical-support, by radek
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One of the most frequent calls we get is how to size/select our Dayus custom grilles.  The answer is simple:  The HOLE size.

The measurement we need to build a grille is the size of the hole/opening (we call it LIST SIZE).  The hole size is the information entered into our website for pricing and ordering.  Dayus will build the grille slightly undercut to make sure the recessed portion of the frame slides nicely into the hole. 

The grille flange is roughly 1″ all around, giving you a finished flange to flange dimension 1-11/16″ bigger than the hole size (list size) you gave us.

Dayus Bar Linear Grille

Dayus grilles:
http://www.hvacquick.com/products/residential/Grilles-Registers/Grilles

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ECM motors on whole house fan…

On June 30, 2010, in cool products, by radek
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The latest trend we see in whole house fan design is the inclusion of ECM motors (electronically commutated motor).  Match that with an efficient blade and you get a great power profile and low noise.

Lets look at the AirScape 4.4e WHF whole house fan as an example.  The graph below shows the energy use profile of the 4.4e as compared to the theoretical efficiency of a fan system.  102 watts on low speed!!

AirScape ECM Fans

This tickles my engineering senses to the point I will probably upgrade my trusty AirScape 1.7 WHF with this new unit.  Smile

More on AirScape Whole House fans including the 4.4e WHF:
http://www.hvacquick.com/products/residential/Whole-House-Fans/Whole-House-Fans

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ASHRAE 62.2 — What is it?

On June 30, 2010, in solutions, by radek
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ASHRAE 62.2 “Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings” is the U.S. national minimum ventilation standard.  Note that not all states require it or may apply it differently so check with your local building codes to see what they require.

The standard requires low-level, continuous ventilation in a home using a whole-building fan or other ventilation system. Intermittent whole-building ventilation can be used as an alternative. Note that the standard uses the term “whole-building ventilation fan”, not to be confused with the term “whole-house fan” which is a different product (see AirScape whole-house fans on hvacquick.com.

To calculate the required flow for continuous ventilation, count 1 cfm (cubic foot per minute) per 100 square feet of floor area of the house. Next, multiply the number of bedrooms plus one by 7.5 cfm (cubic feet per minute). Then add those results together. For example, a 2,000-square-foot house with three bedrooms would require 50 cfm (20 cfm for the building area plus 30 cfm for the 3+1 bedrooms).

Typically HRVs or ERVs are used to meet the standard, but bath fans are acceptable as well.  There are additional sound and minimum cfm criteria that bath fans must meet in order to be allowable.  Fantech and S&P inline fans are a good option due to their low sound levels and available 62.2 control options:

http://www.hvacquick.com/products/residential/Ventilation-Accessories/ASHRAE-62-2-Controls

An online version of the standard is available at the ASHRAE website (www.ashrae.org).

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A Bunch Of Hot Air…

On June 30, 2010, in cool products, solutions, by jake
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Back in the old days, laundry rooms were put on an exterior wall, almost exclusively to provide a short vent run for the dryer. As our houses grew, somehow function trailed form and the unsightly laundry room was relegated to some hidden corner deep inside the house.

Works out for space usage, opening exterior walls for windows and the like…for the dryer, not so much.

Dryers need to shed heat and moisture to operate efficiently. More than 6 feet or so and they are over matched. Well…what now?

Dryer booster fans! These fans have pressure switches or current sensors to know when the dryer is running and turn on and off all by themselves. These fans have enough strength to keep the heat and moisture moving, allowing your dryer to dry clothes in the time it should.

How Do I Know If I Need One?

  • Takes a long time to dry your clothes?
  • Need to run the dryer multiple times?
  • Replaced your dryer because it burned out?

Tjernlund, Fantech, Soler Palau and others make great ones. Give a call to find out which one will work best for you…

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Why you need ventilation.

On June 30, 2010, in solutions, by radek
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Older leaky buildings permitted sufficient air change (fresh air infiltration) to remove pollutants (such as carbon dioxide, moisture, mold spores, formaldehyde from building products) by the natural forces of wind and stack effect.  Newer, tightly built homes do not allow this air exchange.

The best way to introduce fresh air into a home is through the use of an HRV or ERV.  These products allow for balanced ventilation, same amount of air is exhausted as brought into the house, and the majority of the heat/cool is recovered from the exhaust stream into the incoming air.  You get the best of both worlds — good air quality and low operating cost.

Heat Recovery (HRV) and Energy Recovery (ERV) units:
http://www.hvacquick.com/products/residential/Indoor-Air-Quality/Residential-HRV-ERV

Fantech heat recovery units

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Solar attic fans!

On June 30, 2010, in cool products, news, by radek
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Why do we love solar attic fans?  How about easy install, long life, and no energy costs!  Its a great do-it-youself upgrade project or a quick easy job for the pro.

We recently added the AirScape solar attic fans to our lineup.  They are robust, look great and are well priced.  Significantly better than the el-cheapo big box store units… in our humble opinion…

A couple of different sizes and models are available:
http://www.hvacquick.com/products/residential/attic-fans/attic-fans-solar-electric/AirScape-Solar-Attic-Fans

Airscape solar attic fan

And some good news:  the cost of your solar attic fan and installation qualifies for a 30% tax credit under the U.S. Emergency Stabilization Act of 2009. Save your receipt, along with the handy residential certification form.

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Wasted Water!

On June 30, 2010, in did you know, solutions, by jake
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The average family can dump 10,000 gallons or more down the drain every year waiting for hot water.  That’s half a swimming pool wasted!  If only there was a way to save all that water…  hmmmm…

Luckily there is!  A recirculation pump (retrofit or dedicated return line) can save water from being wasted and the corresponding money. 

How do the retrofit systems work you ask?  The problem of course is that water heated by your water heater sits in the line between the heater and the tap(s) where it cools off. Let’s call this “previously hot” water. When you turn on the tap you need to flush out this previously hot water to get to the fresh hot stuff. With low-flow faucets and long plumbing runs, this can take a long time – and waste a lot of water.  An instant hot water system – or hot water recirculation system – flushes the previously hot water back into the hot water tank (rather than you running it down the drain) through the cold water line, so you have freshly heated water waiting for you when you turn on the faucet – instant hot water. 

Metlund and Laing pumps:
http://www.hvacquick.com/products/residential/Instant-Hot-Water/Hot-Water-Recirculation-Pumps-NON-TANKLESS

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The Great Cover Up…

On May 17, 2010, in solutions, by jake
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Those of you living in High Rises or older homes have come up with a great way to beautify the interior of your home…covering up that unsightly steam radiator.

As you can see, there are a multitude of methods to do this. One of the most common ways we have seen is to surround it with a cabinet. The one problem is that heat wants to rise, and generally there is controls that need accessing from time to time…

HVACQuick has you covered! (Nice play on words, huh)

Behold!! The Bar Linear Diffuser! We can make these in very long lengths to cover any Radiator. Also, we can put operable doors on one or both sides to facilitate control access…

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