Ventilating or ventilation (the V in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air.
Heating, ventilation, and air conditioning (HVAC[1]) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation, as HVAC&R or HVACR or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).
I am a service technician [since '92].....and as to double filtering.....I have never recommended it. would be noticeably helpful if the fiberglass filters are the main ones used [which I also never long as system can deliver appropriate air flow with a pleated cotton filter...and any decent service tech can check the air flow for proper cfm]. Any particles small enough to pass through a pleated cotton filter are going to pass through a second filter as well....unless the second filters are so tight that the system is starving for air flow. Has anybody ever accidentally put two filters in their automatic drip coffee maker? What if cars used two fuel filters or air filters? I have told some homeowners to try using second filters at each register [the black thin filter material cut-to-fit....same type used in many window air conditioners].....but I only suggest this when I know they will still get at least 400 cfm per ton of air flow [350 absolute minimum] some homeowners know others who say it has helped and it gives them a peace of mind knowing they are doing something to help contribute to a solution, so it HAS to help [even though I think it falls in the "one-born-every-minute" category.....similar to duct cleaning].
ISO 16813:2006 is one of the ISO building environment standards.[31] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[32]
The amount of time it takes to clean a residential HVAC system depends on many variables such as the size of the home, the number of systems, the extent of the contamination and the number of HVAC cleaners performing the job. Ask at least two contractors to inspect your system and give you a time estimate for your particular system. This will give you a general idea of how long the job should take as well as an idea of how thoroughly the contractor plans to do the job.
A BTU is the amount of energy required to heat or cool one pound of water by one degree Fahrenheit. So a 1-ton air conditioner can cool 12,000 pounds of water by one degree every hour. That’s all it means, so don’t let yourself be lost in jargon! How this affects your HVAC installation cost is that the larger your house is, the more tons will be required to heat and cool it.
PickHVAC Tips: Oil burns dirty, so it is important to have your plenum and ducts checked to see if they should be cleaned when replacing an oil furnace. If you don’t clean the plenum and ducts when replacing the furnace, the new furnace might not run as efficiently and comfortably as possible due to restricted airflow. This can also reduce the oily smell sometimes associated with oil furnaces.
I live in a 1950's ranch house in the South. The prior owners were smokers. Based on recommendations from one of the local conservation organizations, I decided to have a home energy audit done. As part of their findings, they recommended additional insulation in the attic and duct cleaning and sealing. This turned out to be a very problematic process. In terms of the ducts, it was necessary to remove the metal grates. However, these grates had been painted over many times and shoe molding covered the bottom of the grates. The vendor was not able to remove the grates without damaging them in the process. Because these grates dated back to the 1950's, it was difficult to find appropriate replacements. The ones I finally discovered were correct except they were 1/4" wider. This meant that the shoe molding had to be carved out. The duct cleaner could not provide any assistance with this problem. It took me a month of long evenings replacing the vent covers myself, carefully chiseling out the shoe molding and repainting. In terms of the extra installation in the attic, the same vendor used blow in insulation. Unfortunately, they did not recognize that the 13 floodlights whose mounting extended into the attic were not designed to be buried under insulation. The problem manifested itself in terms of expensive flood light bulbs failing continually. So, I had to have all of the light housings replaced. Yet another unexpected expense. Despite the expense, pain and suffering, I cannot report any improvement in my heating costs or the "quality" of the air. To be fair, I do not have any allergies and did not undertake this for air quality improvements but rather heating efficiency improvements.
Roof-mounted systems have the heating and cooling systems in one cabinet. Sometimes called "gas packs" (if the heater uses natural gas), they typically cost less than a comparable split system. In dry regions, most homes originally had "swamp-coolers" installed. When replacing them with HVAC systems, it's often cheaper to use existing mounts and ducting.

The Environmental Protection Agency says that “duct cleaning services typically – but not always – range in cost from $450 to $1000 per heating and cooling system, depending on the services offered, the size of the system to be cleaned, system accessibility, climactic region, and level of contamination” and type of duct material. Consumers should beware of air duct cleaning companies that making sweeping claims about the health benefits of duct cleaning – such claims are unsubstantiated. Consumers should also beware of “blow-and-go” air duct cleaning companies. These companies often charge a nominal fee and do a poor job of cleaning the heating and cooling system. These companies may also persuade the consumer into unneeded services with and/or without their permission. (If you have knowledge of a practicing “blow-and-go” air duct cleaner, contact your local Better Business Bureau to report the company, and your local, federal, and state elected officials to demand legislation.)
I’m really not convinced that duct cleaning is of any value. My roommate wanted the ducts cleaned so he called some company. My scam senses is already tingling. They came in with a big negative pressure fan. Did some blowing and sucking in different vents. Then they tried to upsell a full system cleaning. They wanted to pull the blower and clean the heat transfer box at $700 per heater unit. I have a big house so we have two units. They also tried to sell us some “custom” $250.00 Air Lifetime air filters. At that point I pulled the BS get the hell out bell. After paying $520.00 for just the cleaning, I paid the bill and sent them on their way. I replaced the existing filter with the good old and cheap paper filters at $10.00 each. Duct cleaning… I’m not Impressed.
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.