This seems to come up every summer when it comes to air conditioning. I inevitably come across a few clients that insist that they want to keep their home super cold and swear to me the air conditioning system is too small for their home. Let’s establish a few facts when it comes to buildings and air conditioning systems.
First off, when a home is constructed the builders run what is called a Manuel J load calculation to determine the amount of air conditioning that is needed to properly condition and more importantly dehumidify the space. In the category of stating the obvious, if an AC system is too small it will not properly cool the space; in the not so obvious category is the fact that if it is too large it will create a humidity issue in the area. Oversized units satisfy the thermostat too quickly not allowing it to run long enough to pull moisture out of the air. Hence, bigger is not better.
The second fact that I would like to establish is that on its best day an air conditioner can only cool whatever space it is in by around 25 degrees versus whatever the outside temperature is. So, to the folks out there that set the thermostat at 67 degrees and call me complaining that it won’t go below 72 degrees in the house when it is 95 degrees outside, please just stop. The biggest, absolute best air conditioning system on the planet could not achieve that goal without major humidity issues. If you want to live in an igloo maybe the sub-tropical climate we enjoy here is just not for you.
So unless the home has had additional square footage added to it, the current size of the air conditioning system is likely correct. That said, what can we do if the home will not go below 77 degrees on those 95 degree days? There are several things that need to be looked at. Let’s start in the attic for example. How much attic insulation do you have? In homes built before 2016, I can almost carve in stone that your attic is under insulated. Building code requires a minimum of 12” of insulation in the latest revisions and if you go a step further, we are in climate zone one according to the EPA and 18” is what is recommended. Properly insulating your attic will not only keep the home cooler, you’ll likely reduce your AC electrical usage by 20% or so.
Next up, what is the condition of your duct system? Are there cold air leaks at the connection points in the attic allowing the air that you just paid to cool to escape into an unconditioned space? A quick thermal camera inspection can answer that question. I typically find a 25 year old duct system is losing 30-40% of the conditioned air to the attic. Not only does air loss to the attic make it harder to cool the home, it can lead to mold issues if not corrected. Think about taking an ice cold can of Coke out of the fridge and setting it on the patio table when its 90 degrees out, that can begins to sweat or condensate. The exact same thing can be happening in your attic if you have leaky ducts. Our attics here will easily hit 120-140 degrees in the middle of the day and we are sending 50-some degree air thru tubes in that environment, hence cold air mixing with hot air forms condensation, condensation leads to mold growth. Remember, our little biological friends just need three things to be happy; food, water and darkness. Leaky ducts very much fit that bill.
There are certainly other factors that we need to look at if the house doesn’t cool to your satisfaction such as windows, roof type and doors. Those are things I leave to other professionals to repair, however I can tell you the biggest factor on determining a heat load calculation for a space is the windows. I have seen several thousand BTU’s come off load calculations when switching from old jalousie windows to hurricane glass.
Ok, rant over for today, if your home is not cooling to your satisfaction, give us a ring — we can help, just please don’t ask me to make you air conditioner bigger and we’ll be fine. Until we have gone around the sun a few more times and we meet back here, the batteries in my flashlight died the other day and at first I was sad then realized I was actually delighted.
House Whisperer out!!
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