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HOW TO SELECT AN HVAC COMPANY
It needs to be realized that there are both professional HVAC companies and fly-by-night companies or individuals, as there are in many other professions. Since the average HVAC job will be installed and used for many, many years, it behooves the prudent shopper to acquaint himself or herself with some basic methods that can greatly reduce the potential to end up paying thousands of dollars for what could end up being at least an uncomfortable system and at worst an unsafe, even life threatening system. Below are some suggestions on how to choose a highly qualified company, as well as some editorial information about each of these suggestions.
1. Using the media of choice, go right down the list of each HVAC company and telephone them. Your goal is to ask just one basic question, the answer to which produces significant information about the company. The question to ask is,
“How would your company determine the size of the (heating or cooling) equipment for my house?”
There is only one correct answer to this question. (ed. The DOE and every major product manufacturer all recommend the same method. How the company answers this question therefore tells you whether they follow federal government and manufacturer ‘best practices’ or not. Those that do are far more likely to deliver a properly sized system or equipment to the job. Improperly sized equipment can lead to discomfort, short cycling, higher energy costs and shorter equipment life. Therefore, there is a definite value to selecting a company that answers this one question properly.
Acceptable answers: “By Manual ‘J’ calculation”; “By an engineering analysis”, “By a room-by-room load analysis”; “By measuring and calculating the load for each room”; “By ACCA (Air Conditioning Contractors Association) software”; “By using a computer design” or similar methods that specify an actual mathematical calculation based on solid science.
These companies have spent the time to educate their sales, installation and service staffs. The mere fact that they know how to do the sizing correctly tells you that they care about their reputation and your comfort. The education and materials needed to do the job correctly are a represent a substantial investment in both their business and your comfort. Do not expect any company of this caliber to cheap. In fact, the added value they bring to the table will likely put their quote substantially above a company that guesses at sizes. But wouldn’t you rather know what you’re getting than to have someone guess at the size and gamble several thousand dollars that they guessed correctly with your money?
Unacceptable answers: “By square footage”; “By looking at the size of the existing equipment”; “I’ve got XX years in the business and know how big it needs to be”; “By years or experience”; “By the thousands of units I’ve installed over the years” or variations thereof that say “I guess at the size”.
These are the companies that know only one thing. That is, how to cut corners to the point that they are the low bidder on a job. The first corner to be cut is the time it takes to measure the entire house, room-by-room, window-by-window, check the insulation, determine construction techniques and calculate the actual heat gain or loss of the house and each individual room. If they measure at all, they use a multiplier “rule of thumb” to determine the size of the equipment. They may be right or wrong. It’s your gamble as to which. After all it’s your money right, not theirs? Obviously if they’ll cut that very first corner that you should know they’re cutting, can you just imagine what corners will be cut in areas where you have no knowledge?
2. When you’ve found a company or two that will answer question #1 correctly, invite them into your home and enjoy the presentation. A good company will spend as much time as is needed to make you totally comfortable with the process of what’s happening, why it needs to happen and what you should expect to follow. Comfort comes in many guises and your emotional comfort with the process is paramount to a good company. Please do not be offended when they ask to have all the people involved in the decision present. There’s a huge amount of information to be digested, all of it representing added value this company will bring to the table. To expect one person to relate it all to another is just not going to happen. So please have everyone present who needs to be there. Opinions can vary, questions will arise. All of these issues need to be addressed to everyone’s satisfaction.
3. Once the size of the equipment has been determined (do not expect the sales person to share the equipment size with you until after an agreement has been signed. They’ve been burned too many times by customers who get them out to determine the size of the equipment and then use that information to get a lower price. In the end, the client gets the right size but a hundred other corners were cut, leaving the homeowner once again, cheated) you should expect the duct system to be designed according to Manual ‘D’. That is the ACCA method of designing a duct system that will deliver the proper airflow without excessive noise. It’s important to note that the ducts can’t be sized until the equipment is properly sized. That once again would lead us back to the importance of that question you’ll be asking in item #1.
4. Finally, after the equipment and ducts are properly sized (or in the case of ducts, reviewed as to current condition and sizing) it’s time to select the equipment itself. Brand is not normally very important and many companies can offer more than one brand. All manufacturers have both successes and failures of equipment most importantly based on the installing company. Once again, the installation company that follows the proper procedures will deliver the anticipated result to you. If corners are cut, you can expect discomfort and problems.
Sizing Heating and Cooling Systems
Older space conditioning systems (more than 10 years old) are often unreliable and much less efficient than a modern system. When it's time for a new replacement, choosing one of the correct size (heating and/or cooling output) is critical to getting the best efficiency, comfort, and lowest maintenance and operating costs over the life of the new system. Some national surveys have determined that well over half of all HVAC contractors do not size heating and cooling systems correctly.
The most common sizing mistake is in oversizing. This not only makes the new system more expensive to install, but also forces it to operate inefficiently, break down more often, and cost more to operate. Oversized heating equipment also often creates uncomfortable and large temperature swings in the house. Oversized air conditioners (and heat pumps) do not run long enough to dehumidify the air, which results in the "clammy" feeling and unhealthy mold growth in many air-conditioned houses (see dehumidifying heat pipes as one solution to this problem).
Incorrect Sizing Methods
It is the installer/contractor's job to perform the correct sizing calculation for the building. However, many installers only check the "nameplate" (the label on the unit that has the Btu per hour output among other things) of the existing system and sell you one just like it, or even worse, one that's larger. This is a not a correct sizing method and not in your best interests! Other methods include simple "rules of thumb" based on the size of your home or using a chart that accounts for a variety of factors. While these methods might provide a first estimate, they should not be used to size your system.
Why Most Older Systems are Oversized
Before the era of tightly constructed homes, it was not uncommon to install furnaces and air conditioners that had two to four times the necessary capacity. Since many people have added new windows, caulking, weather-stripping, and insulation to their homes, going by the nameplate is likely to result in an oversized system. Making improvements such as these to reduce heat loss in the winter and heat gain in the summer should allow you to install a smaller systems while still being comfortable, as well as saving large amounts of energy.
Manual J and Manual D: The Correct Way to Size a System
Correct system sizing requires considering many factors other than simply reading the nameplate of the existing unit. Key factors for correctly sizing a heating and cooling system include the following:
* The local climate
* Size, shape, and orientation of the house
* Insulation levels
* Window area, location, and type
* Air infiltration rates
* The number and ages of occupants
* Occupant comfort preferences
* The types and efficiencies of lights and major home appliances (which give off heat).
Homeowners should insist that contractors use a correct sizing calculation before signing a contract. This service is often offered at little or no cost to homeowners by gas and electric utilities, major heating equipment manufacturers, and conscientious heating and air conditioning contractors. Manual J, "Residential Load Calculation," published by the Air Conditioning Contractors of America (ACCA), is the recommended method for use in the United States. There are also many user-friendly computer software packages or worksheets that can simplify the calculation procedure. You should make sure that the procedure used by the contractor follows Manual J.
If ducts are part of the installation, they should be sized using the ACCA's Manual D, "Residential Duct Design." The ACCA also offers a comprehensive guide for choosing home heating and cooling systems, called Manual S, "Residential Equipment Selection."
A Special Case: Sizing Steam Heating Systems
One exception to the above is in steam heating systems. For these systems, the boiler should be sized to match the radiators. However, there is still room for energy savings. First of all, the original boiler may be oversized for the radiators, so the contractor shouldn't just order the same capacity boiler, but instead should match the boiler to the radiators. Second, if you've increased the energy efficiency of your home, it may have more radiators than it needs.
It may be possible to remove radiators in the core of the house and shift the others around, replacing larger radiators with smaller ones. Since radiators are modular, it is theoretically possible to downsize a radiator by removing sections; in practice, this is usually difficult to do without damaging them. In many parts of the country, used radiators are available cheaply, so you can potentially buy small radiators to replace large radiators; if you do so, be prepared to replace the shutoff valves as well, since they often won't match. Newly manufactured steam radiators are available as well.
In any case, you should work with a heating and cooling professional when downsizing your system. Your house's heating needs should be calculated using Manual J, and your radiators should be downsized appropriately. Match the new boiler to the remaining radiators. Note that balancing steam heating systems is more an art than a science; ideally, you will find a heating professional with experience in steam heating systems.
Steps a Good Contractor Should Take to Size Your System
Many factors affect a home's heating or cooling requirement, or "load." A good estimator will measure walls, ceilings, floor space, and windows to determine the room volumes, and will assess the R-value of the home's insulation, windows, and building materials. A close estimate of the building's air leakage is also necessary. A blower door test is the best way to measure air leakage.
A good estimate will also include an inspection of the size, condition of seals on joints and insulation, and location of the distribution ducts in forced air systems. The placement of supply and return registers should be appropriate for the system type and size.
The orientation of the house also affects heat gain and heat loss through windows. Overhangs can reduce solar gain through windows. Make sure the contractor uses the correct design for the outdoor temperature and humidity in your area. Using a higher summer design temperature results in oversizing air conditioners.
When the contractors are finished, get a copy of their calculations, assumptions, and the computer printout or finished worksheet. This is your only proof that they did the job right. To summarize, when designing your new heating and air conditioning system, the contractor you choose should do the following:
* Use a computer program or written calculation procedure to size the system
* Provide a written contract listing the main points of your installation and includes the results of the heating and cooling load calculation
* Give you a written warranty on equipment and workmanship
* Allow you to hold the final payment until you are satisfied with the new system.
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