Duct Work and High Ceilings - I did not see any reference to my question and would appreciate a response as soon as possible, as due to medical situation, have to make a decision soon. We own an OLD house with 13′ ceilings in a large part of the home and 11″ ceilings in the LV/DR and BR. We are oscillating on where to place the ducts….Floor or ceiling. It appears to be counterproductive to me to put the duct work in the ceiling since it will have so far to go. We are looking for the most cost effective, not upfront cost but operating cost, solution. In addition, we are considering DF heat pumps. The house will need 2 or 3 to be zoned correctly. Please let me know about the duct placement and thank you for your help? Continue reading
Air Conditioning and Heating Sizing - How many tons of air conditioning and heating do I need per square foot?
Rules of Thumb
It is not uncommon for HVAC estimators or HVAC contractors to use various rudimentary techniques which are generally referred to as rules of thumb. Some will say on the low end you need 1 ton of cooling for every 500 square feet. On the high end you will need 1 ton of cooling for every 700 square feet. These rules of thumb will also generally take into account a basic heat gain calculation for the kitchen and the number of people who will occupy the structure. At best these rules of thumb are educated guesses and may not give you an accurate calculation of what you really need. Unless the contractor used software based on the above mentioned manuals it would be to your advantage to actually do a proper load calculation for the structure based on Manual “J” or Manual “N” whichever is appropriate for your HVAC application.
Air Conditioning and Heating Sizing - Air Conditioner and Heating Ductwork
Manual “D” is used for sizing residential ductwork for the appropriate amount of airflow. For each ton of air conditioning you will need 400 cubic feet per minute (CFM) of airflow. It is imperative that this amount of airflow (400 CFM) be provided to the air conditioner evaporator coil of the air conditioning system. If the ductwork is too small it will restrict the amount of airflow crossing the air conditioner evaporator coil and this will likely cause big problems. If the ductwork is too big the system may have a problem generating enough static pressure to maintain designed airflow across the coil. The proper design and construction of the air conditioning and heating duct work is important for the proper functioning of the system. Using the proper techniques, software, and skilled personal will ensure that the HVAC job is accomplished correctly and will provide many years of reliable and efficient comfort to you.
Air Conditioning and Heating Sizing
Using good and time tested methods to size air conditioning and heating systems for your home or business is a smart thing to do. Using an HVAC estimator who is going to employ a rule of thumb for something that will be attached to your home and provide you with comfort for 15 to 20 years is not so smart. Use proper HVAC sizing methods and you will be better off and comfortable in the future.
Air Conditioning and Heating Sizing
As the cost of energy rises engineers are looking for ways to improve and increase energy efficiency. Aside from HVAC equipment with higher energy efficiency rates, improving structures for less heat loss and heat gain, and building automation systems giving the equipment precision control for better efficiency of the equipment, there are other ways to increase energy efficiency inside buildings. One of the ways to increase energy efficiency inside buildings is to add energy recovery wheels to the economizer systems. A US Department of Energy study concluded energy recovery wheels can save over 15% of the energy used in commercial HVAC applications.
A good consideration when replacing the air conditioning system is the duct work. Duct work seems to be the most ignored part of an HVAC system but is a very important consideration in this age of new technology and higher energy efficient equipment being developed and manufactured. You can have the most energy efficient engine but if its in an old 60 or 70’s model car your efficiency is going to suffer. The same is true with HVAC systems. You can have the most energy efficient compressor available on the market but if your duct work is leaky or your house or business is not properly insulated that high efficient system you just spent big dollars on is wasted money. For more insight on HVAC ductwork see the High Performance HVAC Ductwork Page. Continue reading
Labor time (approximate): 1 hour in some cases, several hours in others
It is important for preventive maintenance to be performed on your system to avoid problems. Condensation water leaking near the air handling unit can be avoided with proper air conditioning repair and preventive maintenance. Normally this is a very simple problem that can be fixed in less than 30 minutes. Here is a list of what can cause water around the outside of the air conditioning air handler unit.
- The black insulation (called Rubatex) has a tear in it or doesn’t cover the entire suction line. This line normally (in Air Conditioning air condition mode) operates below the dew point and will sweat if it is not insulated. It must have a sealed vapor barrier to be effective.
- The insulation surrounding the air handler supply transition or ductwork is torn. The supply transition and duct can operate (under the right conditions) below the dew point and sweat. It is important that the transition have a vapor barrier around it. This scenario is especially true for those that have over sized units.