Before central air conditioning, evaporative coolers, also known as swamp coolers, helped keep homeowners cool. Many older homes in Phoenix had no central air when they were first built, and remnants of the original swamp cooler are often still visible in a home, such as upducts or a cap in the roof where the evap cooler used to be located. The advantage of using the evap cooler is lower energy bills because the evap cooler only uses a large blower motor to blow air over a filter drenched in water. Many homeowners who have evap coolers try to hold out on using their AC as long as possible but when the temperature rises above 100 degrees in Phoenix, the evaporative cooling just can't cut it.
Because the evap coolers are so much less to operate, many homeowners figure that they it's cheaper to run the evap cooler in May and June and then switch to central air for July and August. How much does that method really save though? As energy auditors and home performance contractors we have seen dozens of homeowners faced with this situation. The short answer is that homeowners will save more money (and be more comfortable) by capping and sealing the evap duct and just using their central AC in the summer if the ducts are sealed, the home is sealed from the attic and insulation is up to R-38.
For some homeowners, we are able to cap and seal the evap duct connections to perform a proper sealing and insulating of the attic. Some homeowners have a tougher time letting go, as it may be like parting ways with a favorite t-shirt. The homes that have their evap cooler connection still in place will have minimal change in their bill, even if a duct seal, air seal and insulation upgrade is done! We have heard from homeowners that do eventually cut ties with their old evap cooler that they have all seen a great reduction in the following energy bills as we have followed up with them.
Surprised? When our energy auditors measure the duct leakage on a home with an existing evap cooler connection, that leakage is sky high! The dampers on evap duct systems are ineffective and a major source of leakage. The damper will cause a 4 ton AC unit to put out only 3.5 tons of air. Add to that the air leakage and heat gain from the upducts located in each room and you have a recipe for high energy bills. There are replacement dampers for evap ducts and some are actually pretty good. The problem is finding an AC contractor who can source and install them. If duct sealing is done with the evap connections still in place for future use, the major source of leakage is still present after the work is done, which is why energy bills will not do down that much. When a home is properly sealed, the ductwork is tight and a thick insulation blanket is keeping all the conditioned air inside the home... bills go down and the cost savings begins!
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