The amount of debris or mold present in your system could certainly ratchet up the overall price. The cost of mildew removal is around $0.07-0.08 per square foot, on top of your initial cost, according to Blue Book. Removing these elements involves added time, special equipment and even special chemicals. In fact, you may be referred to a specialist if mildew and mold is too severe.
I need a complete system replacement , before I was trying to get an evaporator coil replaced , of course the price is between $2200 an $2800 , then get told it probably will over tax my ac unit within months , so now and like everyone else what do you buy 14 ,15 16 17 seer units ,price and how do we know its reasonable  why can't there be '" a estimated price ,in the ball park, a range of prices ,so we can at least go from their .....  Now it's from 7500 to 15000. Frustrating  from the start so everybody good LUCK.   Draw a # from the hat    Unregulated  and who do you BELIEVE, just like on NCIS go with your gut feelin   
I'm very glad that I found another guy to come replace the circuit board and put it away from the water, fix the water leak, and also find and fix another impending failure.  All of that was for much less than HVAC Service wanted to charge for repair or replacement. The other guy did a great repair, so I'm confident it will not break down again, but if it does, I will not call HVAC Service. Don't get suckered by their Yelp Deal.
Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.
I am 79 years old, bought a condo & spent a lot of money on it. this winter my first bill was 450.00. had my furnace checked out, which is on the roof. it was old rusted out & leeking oil. i talked to owner & had new unit installed. they came out to clean ducks & they were split & worn out. there is no crawl space because theres a unit above me. my real estate lady or this company will not help me fix this problem.
In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.

We moved to a house built in 1965 from a 1915 house with a dirt basement. Against what I anticipated, the 1965 house was much dustier. It was like felt on top of everything. I cleaned and cleaned and it did become less dusty over time. We then found out a cat lady with over 2 dozen cats lived in the house in the past. We then had to get our furnace replaced and I was able to look down some of the duct work, the dirt and debris was 3-5 inches deep. Additionally, the basement ducts were entirely plugged with debris including dirt, seeds, ants, toys, etc. I had already removed what I could from those. We had our ducts cleaned last year, and the dust in the house is greatly reduced. Also have lost the runny nose I got after moving here. There are duct cleaning con artists out there, but ours did a good job.
Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.
Installation: The old furnace is disconnected from the ductwork plenum, exhaust flue, gas and electrical hookups. In most cases, a new plenum must be made onsite or ordered from a local sheet metal fabricator. A new vent might be required too. The furnace is set and reconnected. Adjustments to the blower fan speed and burner are made to optimize furnace performance for your home and climate.
Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.
Two weeks go by and no phone call from HVAC Service regarding install date, or any update at all.  I call them to check in to see if they have put me on the schedule and when I can expect to have the AC installed.    You can tell by the discussion I had with the lady on the phone that they completely forgot about me and have not scheduled anything.  She says she needs to get in contact with the owner because she has no idea on the availability of the crane.  I was told that she would call me back by the end of the day with an update.  Surprise, surprise, no phone call.  
While you consider having your air ducts cleaned, it is a good idea to take a look at your dryer vent. If your dryer vent is clogged, you could be losing energy efficiency. Worse yet, you could be increasing the risk of a house fire. Having your dryer vent professionally cared for costs about $130 on average, and could save you a bit of money and a lot of headaches in the future. For more information on the benefits and cost of having your dryer vent cleaned, take a look at our comprehensive cost guide.

I even asked if this is something they don't do, as in services on a Saturday night.  I was told by the receptionist that they do and I would just be ok calling another company if they is not  part of their services. They again assured me someone WILL call me in 10 mins.  Well, unless their definition of 10 mins is never, then they got it wrong as I am still waiting to be called 5 days later.
Window air conditioners cost less than central units, averaging $300. These systems generally suffice to keep a room cool on warm spring and summer days. They can bring added comfort for a reasonable price but are less powerful than a central air conditioner. If you have a bigger home with multiple rooms, you will probably need to have a larger system installed. Central air can cool several rooms at once, while window AC units usually only cover one or two rooms at a time.
So, whether you need an AC repair or you’re in search of a new heating and air conditioning system—or you need a new water heater now–you can count on our team in North America. We’re experts in AC and plumbing repair, and offering top-notch AC and plumbing service is what we do best. Call Service Experts 24/7/365 at 866-397-3787 or request an appointment online today, and don’t forget to check out our coupons page for savings on your AC or plumbing repair service.
Manufacturers of products marketed to coat and encapsulate duct surfaces claim that these sealants prevent dust and dirt particles inside air ducts from being released into the air. As with biocides, a sealant is often applied by spraying it into the operating duct system. Laboratory tests indicate that materials introduced in this manner tend not to completely coat the duct surface. Application of sealants may also affect the acoustical (noise) and fire retarding characteristics of fiber glass lined or constructed ducts and may invalidate the manufacturer's warranty.
The key to the continued and efficient operation of your heating and cooling system is periodic maintenance. Cleaning the air duct vent system, and servicing you heating and cooling equipment will keep the system operating at its peak performance. Air ducts are cleaned for two reasons. One: to prevent debris from entering furnace and air conditioning components. Two: to prevent debris from cycling through the home. The air duct cleaning contractor needs to employ cleaning methods which successfully removes debris, and ensures that debris does not enter the occupied space. Most contractors can verify the results of the cleaning through video or pictures.
Yes, ducts can look terribly dusty. However, that dust will not become aerosolized during the normal operation of your furnace. There is an easy way to test this. Rent a particle counter and test the air flowing out of your registers before and after cleaning. You will not see any improvement in the air quality or any reduction in the airborne dust level. Think of it this way. Duct cleaning companies tell you that you need to clean your ducts when you can see a layer of dust in your ducts. Yet that very layer of dust is proof that duct cleaning is unnecessary, because that dust proves that the air movement in your furnace is not fast enough to re-aerosolize the dust.

Important Tip: Don’t just pay attention to the high-end of the price range! – which is what I know you are all looking at, but also look at the low range. If a contractor is cheaper than this, ask “why?” Usually it is because they don’t have liability insurance, workman’s compensation insurance, are unlicensed, all of the above, or worst yet, they don’t use HVAC technicians. You are spending a lot of money.  Make sure that they are licensed (In California, check here at CSLB License Checker) and insured.

A year and a half ago (fall of 2015) we replaced the furnace and air conditioner. From what we could determine this was the third forced air furnace and second air conditioner unit for the house. As part of the installation, we changed out the two 6″ ducts feeding the second floor with 8″ ducts. The idea was to get more cold air to the second floor in the summer. It worked and for the first time the second floor and first floor temperatures were the same when the air conditioner was running. Of course, to make the system work I close down upstairs duct damper doors in the winter and open them up in the summer.
I'd have to disagree with all of your statements. Not only are they derived from no experience in the field, you are missing keys facts. Ducts even if air tight will get dirty. If they are not getting dirty, it means they are not working. Your returns side of the duct work is always under negative pressure when the system is operational.Therefore it is always drawing air in. Seeing how dust is made up mostly from dead skin humans shed daily. Around 1.6 Pounds of skin a year per human. Living in your home anything that is air born will be drawn back towards the cold air returns. That is what they are designed for, to draw stale air back to the system to be filtered and sent back through the house.Homes with carpet will actually have cleaner duct work than home with all tile or hardwood. This is because carpets hold onto dust particles and you vacuum them up. Whereas on hardwood or tile, dust can run freely back to the returns. Even if a duct system was sealed 100%, which is next to impossible to achieve 100% would still need to be cleaned. The cleaning may only have to be every 7-10 years for example. Most homes require every 5-7 years. And that's if it was done properly the first time. If you constantly hire people that have no or minimal knowledge of duct cleaning, You home would require cleaning more often. Every 2 years. That's a trade secret, The longer they recommend before the next cleaning, the odds are they did it right. That's not to say there aren't people that lie, because there are. Just have your duct cleaner take pictures before and after cleaning. Not just an outside view. Get in there, picture entire joist liners, Whole main runs and even long round pipes. Also it helps to have a company that guarantees their work. If it's not done right, they will come back and do it until it is. Most companies that do this make sure it is right the first time. Your not getting paid to do the job twice.
Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.
The most recognized standards for HVAC design are based on ASHRAE data. The most general of four volumes of the ASHRAE Handbook is Fundamentals; it includes heating and cooling calculations. Each volume of the ASHRAE Handbook is updated every four years. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.

Preventing against air leakage is great, but the only way to keep dust and debris out of a duct system would be to completely seal off the return-air side of the system, which would render the system useless. Cold-air returns will always pull dust and other particles into the system. A high-MERV rated filter is definitely a good idea, but it does nothing to keep the return side of the system clean. Definitely agree though to use foil tape to seal seams, etc. Duct tape dries out over time and as it does can actually add more particles to the air.
In addition, the service provider may propose applying chemical biocides, designed to kill microbiological contaminants, to the inside of the duct work and to other system components. Some service providers may also suggest applying chemical treatments (sealants or other encapsulants) to encapsulate or cover the inside surfaces of the air ducts and equipment housings because they believe it will control mold growth or prevent the release of dirt particles or fibers from ducts. These practices have yet to be fully researched and you should be fully informed before deciding to permit the use of biocides or chemical treatments in your air ducts. They should only be applied, if at all, after the system has been properly cleaned of all visible dust or debris.