Top 4 Things That Interfere With Central AC

By Carl Seville, Networx

Plenty of people who run central air conditioning systems in Houston (and other cities where  hot weather dominates the calendar) complain  about how their air conditioning  doesn’t do a good job keeping their  home comfortable, and, in most cases, they  are probably right.  There  are so many things that can and do go wrong  with central HVAC systems  that it’s tough to know where to start, but I’ll give  it a shot.

1. Leaky ducts

Probably  the single biggest cause of poor AC performance is leaky  ducts.  Ducts  are kind of like pipes – they move air through them and  deliver it at  the end.  We notice when our water pipes leak because we see  the damage  immediately, but we rarely see the effects of leaky ducts directly; rather it sneaks up on us over a long  period of time, and  many people never figure it out.  When ducts leak,  they let cool air out  into whatever space they are in, often the attic, which,  in case you  haven’t noticed, can get pretty hot in the summer.  Ducts need  to be  sealed at all the metal-to-metal and metal-to-flex connections – not at   the insulation.  Have someone pull back all the insulation and put a  nice  thick layer of goopy mastic at all the joints, then replace the   insulation.  Don’t use duct tape. It won’t work, and the metal tape   designed for ducts doesn’t do a whole lot better.

2. Too much or too little refrigerant charge

Something  else that can make your AC inefficient is the refrigerant  charge.   Traditional AC uses a refrigerant that transfers the heat between  the  inside and the outside.  Every system is designed to work efficiently   with a specific amount of refrigerant, and too often there is either too  much  or too little in the system.  A  good HVAC contractor can check the charge and either add or remove some to  make sure it is  set correctly.  A wrong charge can decrease the efficiency  by 20-30%, so  checking and fixing this can make a big difference.

3. Installing the wrong filter

Make sure you have the right filter installed.   Most HVAC systems  were designed to use one of those cheap fiberglass  filters to clean the  air.  Unfortunately, they don’t do a very good job  at it, so many people  go to their local hardware or big-box store and  buy a super-duper high  efficiency pleated paper filter GUARANTEED to  keep their air cleaner.  It  might actually keep the air cleaner, but it  also cuts down on the air flow,  making the whole system less efficient.   They can make the cooling coils  freeze, creating even bigger problems.   If you really need a good filter,  first seal the ducts to keep the air  in and the nasty stuff out, then get a 6  inch thick pleated filter which  fits into a special cabinet which your HVAC  contractor can install for  you. They do a good job filtering the air and don’t  cause the same  problems with the air flow.

4. Not enough return ducts

The  last thing I’m going to talk about is return ducts. Lots of HVAC   systems are installed with a single, large return somewhere in the  middle of  the house.  Each room has its own supply, but the air is  supposed to, sort  of magically, slide under the door and get back to the  big return duct to be  cooled again.  The problem is that the space  under the door usually isn’t  big enough, so the air doesn’t flow through  the whole house well enough to keep  things evenly cooled.  Some rooms  are hot, some are cold, and none are  just right.  Consider having an  HVAC contractor add some extra return  ducts in bedrooms and other rooms  with doors (except for bathrooms) to give you  better air flow and  increased comfort.

Notice that I haven’t said anything about  equipment efficiency.  That’s  what the manufacturers and installers talk  about, because they can make a lot  of money selling you fancy,  expensive air conditioners that are super  efficient.  The problem is, if  you put one of those on a system that is  otherwise pretty crappy, you  have wasted most of the super-duper efficiency you  paid for. Take care  of the more boring, tedious, and important things like  these first,  before you install new equipment.  You’ll be much happier,  and more  comfortable.  Then when you want to put in that super duper  equipment,  you’ll have a really good HVAC system.