An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which have thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[17]
While your HVAC filter is designed to trap particulate matter and prevent it from entering your air ducts, particles often still get through. The number of particles your HVAC filter traps is directly connected to the quality of air in your home: the lower the quality of air, the more particles will be present, and the more particles are likely to get through the filter. If these particles are allowed to build up, your HVAC system can become less efficient, operating longer to heat or cool your home. An inefficient HVAC system can result in inconsistent heating or cooling, higher utility costs, and expensive HVAC unit repairs, such as an A-coil or blower motor replacement if the problem is left unchecked. Air duct cleaning from Sears, which focuses on the dirt in your air ducts, can boost the efficiency of a dirty HVAC system, cleaning out the particulate matter that can hinder HVAC effectiveness and affect your health.

Metal is way better than flex duct or ductboard. It gets better airflow, holds up to critters and duct cleaners. I know of no hvac company here that cleans ductwork. (there probably is one somewhere) The mfg's of duct cleaning equipment keep trying to sell us hvac people on their benefits and profit potential but most all hvac people know that unless you have metal ductwork you are NOT doing the customer any favors.
There are many interesting comments from several informed individuals. The question that has not been answered is how do duct systems get dusty and dirty? As a RESNET Home Energy Rater, I perform pressure tests on homes and duct systems, and the one common thread is . . . most air delivery sytems have large amounts of air leakage. The solution is to seal the duct system, and pay particular attention to the return duct system and ductwork near the air handler (the 'blower'). As others have said, a captive (sealed) duct system with proper filter maintenance should be more then adequate for most occupants. For those who have allergy, asthma, or other breathing problems, a filter with a higher MERV rating (number should be listed on the package) or a HEPA filter are good choices. These filters will capture smaller particulates and should improve the indoor air quality. Again, make certain that the entire duct system is sealed, preferably with mastic, second choice UL-181 foil tape - never use cloth duct (also known as duck) tape.
Stick with a maximum of 16 SEER units in most cases.  Like I said above, contractors push higher SEER units because they make more money, but these units can be expensive at this stage of development, and can drive up your HVAC installation cost.  21 SEER units run about twice the price of a 14 SEER unit, so unless you live in a desert and plan on being there for 30 more years... Likewise, a 16 SEER unit typically costs only about $600-$1,000 more than a 14 SEER, and will usually pay for itself over the lifetime of the unit.
He proceeded to clean each heat register by removing the grille and blasting it with an air pressure hose toward the duct opening thinking that the dust would magically be sucked inside. In one room this caused a ceiling smoke detector to go off because the excess dust fooled it into thinking there was smoke. I put my hand in front of a register he wasn’t working on and could hardly feel a suction. Although we discussed how I open and close damper doors, I realized later that he never checked, opened or adjusted them during the cleaning. He could have closed all but the one he was working on in order to increase suction results. His next step was to blast air into the duct and then attach a “squid-like” device that slapped around inside the duct as far as he could reach. This is important! In a newer house, ducts have long straight runs from the furnace. In older houses like mine they can turn and twist. In fact, the duct we have a problem with runs straight up from the basement inside a wall and turns 90 degrees into a soffit for three feet then into two 90 degree turns to get into the floor joist area for another two feet and finally a 90 degree turn up to the second floor register. When he cleaned this one he could only get three feet into the register with the hose or squid because of the turns. That was the case with most. Hardly what could be described as a decent cleaning.
An EER certifies the cooling efficiency of HVAC units. It's calculated by the rate of the cooling in British thermal units (Btus) per hour and divided by the rate of energy input in watts at a specific temperature. The calculation goes as BtuH/WATT at dry bulb (db) versus wet bulb (wb) temperatures. The optimal rating for a cooling unit is about 80db/67wb inside and 95db/75wb outside.
How exactly do you expect to kill or remove mold without it ? You can’t even clean your hvac systems coils without moisture of some type ,if you use a steam cleaner you can literally clean the whole system minus the electronics . You should do more research and possibly talk to people who do the work before posting , but don’t listen to me i only have a class A contractor license ,epa license , install /repair hvacs , rent and flip houses for a living .
HVAC equipment is estimated to last about 15 to 20 years. Yet over the years, parts go out and need to be repaired. Heat sensors, exchangers, and ducts can become worn out. Air conditioning motors may need repairing from time to time. For repairs to your heating and air conditioning systems, and even general maintenance, let HomeAdvisor help. Enter your zip code and let us connect you with prescreened HVAC repair services near you.
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