Top 4 Things That Interfere With Central AC

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.

Air Sealing Tips for Hot Humid Climates

by Chaya, selected from Networx

By Carl Seville, Networx

Since we’re heading into the summer, and it may well be a hot one  this year,  it’s a good time to look at home improvements that can help  save energy and  make your house more comfortable in those hot, sticky  months coming up. Air  conditioning installers in Miami and other hot, humid climates are going to  get a lot of work this  summer. How can you get the most from your investment in  air  conditioning?

The first thing that homeowners and contractors need to understand is that air sealing is really  important.  The most  common insulation, fiberglass, doesn’t work very well  when air leaks  through it.  It’s actually a pretty good filter for dirt  (you may have  noticed that it’s used for those cheap furnace filters), when you  cut  open an old insulated wall you usually see big streaks of dirt where air   has been blowing through the insulation for years.  Not only do air  leaks  keep the insulation from working, they let lots of humid air into  the house,  making your air conditioner work harder.  Tightening up those  leaks keeps  the house more comfortable, keeps the humidity lower, and  saves a lot of energy  in the process.

So where do we need to air  seal, you might ask?  Pretty much  everywhere, but let’s start at the  bottom.  For now, I’ll assume that you  have a wood framed floor with a  vented crawlspace below it, and probably  fiberglass batt insulation  installed between the floor joists.  Carefully  pull out the batts around  any big holes like tub drains, pipes, big wires, and  any other place  where there are holes in the floor decking.  Plug those  holes with foam  boards, spray foam, or anything else that won’t let air pass  through.  Don’t jam fiberglass insulation in the holes – it won’t air seal   anything.  Then carefully caulk all the small holes where wires and  pipes  pass through the floor.

Finally, make sure that all the  insulation is pushed up tight against the  subfloor and held in place  with skinny metal bars called tiger teeth.  If  you’re really ambitious  you could seal and insulate your crawlspace, but that’s a little too involved  for this post.

Then  you need to go inside and caulk all the cracks between the walls and   the floor.  If you’re replacing carpet or refinishing wood floors, put a   good bead of caulk or spray foam between the baseboard and the  subfloor.   Next, start moving up the walls, filling in all the gaps in  the drywall –  around receptacles, pipes, wires, window and door trim,  and anything else that  makes a hole in the wall finish.  You can buy  foam gaskets to put behind  electrical plates that will help seal them  from more air leaks.  If you  have any knee walls – walls between  interior space and attics, make sure that  they are well insulated and  have a solid air barrier on the attic side –  something like drywall or  foam board, carefully caulked at all joints and  edges.  If your house is  missing this, all the heat from the attic will  flow right through the  insulation into the room, making it really  uncomfortable.

Finally,  we need to fix up the ceiling.  This is where we usually get  the most  air leakage, particularly in the summer.  Go up in your attic and  start  pulling the insulation away from the walls, pipes, wires, and any other   openings in the ceiling.  Seal those holes the same way you did the ones   in the floor, making sure that you get all of them.  You should also  seal  the crack between drywall and the wood wall at the top – that’s a  big air leak  in most houses.   But the biggest ceiling leak is the attic  stair or  access hatch.  You can build or buy a nice foam box to seal  over the top  of them, but you have to be careful about putting them back  every time you go  into the attic.

If you’re not interested in taking on this project yourself, think about hiring a weatherization contractor to inspect the house and  make the repairs for you.  If you’re lucky,  your local utility may offer  rebates for doing improvements like these –  you can be more comfortable, save  energy, and get a little money back  in your pocket.