If you are using existing ducting, it will have to be inspected. Proper ducting loses around 2% to 5% of your energy. Old, leaking ducts can lose 50% or more. A contractor will need to have the ducts inspected and replace any parts ahead of time. If you are changing the size of your HVAC system because of significant changes to your home, you might need to replace the ductwork regardless.
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.
CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:

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.
Do you live in a historic home and want to tie your new system in to work with existing features? The price will go up to do the job right. All of these things add up to slow down the HVAC company, which takes more time, which costs more money for labor and parts. This is especially true if they are a legitimate company which is licensed, bonded and insured. Simply put, this is the “X-Factor” in your HVAC installation cost. Again, you could get people to do it for cheaper…but you won’t be happy with the results, I promise.
Replacing a capacitor is easy. Just take a photo of the wires before disconnecting anything (you may need a reference later on). Then discharge the stored energy in the old capacitor (Photo 4). Use needle-nose pliers to pluck one wire at a time from the old capacitor and snap it onto the corresponding tab of the new capacitor. The female crimp connectors should snap tightly onto the capacitor tabs. Wiggle each connector to see if it's tight. If it's not, remove the connector and bend the rounded edges of it so it makes a tighter fit on the tab. When you've swapped all the wires, secure the new capacitor (Photo 5).

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.
It's always changing: Some newer thermostats take advantage of wireless technology. You can adjust your thermostat remotely so that if you leave and forget to adjust it, or if you are going to be home later than you thought, you can adjust it via your smartphone. Some can even give you reports on how efficient your system is performing based on usage. These are very efficient models, but they are also very expensive with some costing over $250.00.
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