Quote:
Originally Posted by MK2750
The number one concern of a qualified HVAC estimator should be the duct work. Furnaces and air handlers are not pumps. The amount of air they are able to move is completely dependent on the size of the duct work, number of supply outlets and return air. Any contractor that does not count your vents, measure the exposed mains and calculate the air flow using a calculator, should be shown the door. The only exception is an experience contractor that actually designed and installed the duct work in your home or knows the exact duct design of the house you are living in. Always make certain he checks for proper return air in the lower levels or your nicely finished basement will be colder than a meat locker. This is especially true when your house was designed around in floor heating where inexperienced or lazy contractors feel they can get away with inadequate air flow. He/she should also ask specific questions about the comfort of your home and if you have had any airflow concerns or hot/cold spots. These are often easily dealt with by better balancing a system, adding a run or two, or adjusting the furnace or air handler.
The second step is determining the air flow capacity of the furnace/air handler. The furnace/air handler CFM out put is generally clearly marked on the manufacturers plate. It is also included in the model # of the unit. An experienced contractor should be able to point this out to you however you can look your furnace up on line if you have doubt.
If you have not got it yet, air flow is everything in HVAC, especially the AC part. An AC coil needs 350 to 400 CFM of air flow per ton or it will ice up and cost you a fortune to run. Some may still cool your home but when you get your electrical bill you will still be over heating.
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With ^^^ being said, I have often wondered how a resi contractor determines the
actual air flow of an existing installation where the homeowner doesn't want a new furnace? Do any of the contractors do traverses or static pressure curves to determine the true operating point of the blower?