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Why selecting and sizing your HVAC system is critical for healthy air (and what to do when it’s not sized or balanced correctly)

Why selecting and sizing your HVAC system is critical for healthy air (and what to do when it’s not sized or balanced correctly)

A home’s HVAC system may seem like a commodity when building a new home, but it’s one of the most important selections you can make for your health.  When purchasing an existing home, it becomes apparent very quickly if the HVAC system “fits” the needs of the home!  An HVAC system needs to be (health effects are prioritized first!):

  • Sized correctly:  This means that the main equipment (compressor, evaporator and air handler) are not too large or too small for the cooling and heating needs of the home.  Having excess capacity in an HVAC system is just as bad, or worse, than having equipment that is undersized, because the units may cool, but not adequately dehumidify the space.  HVAC contractors should be able to calculate the thermal needs of your home in order to specify this equipment.
  • Balanced correctly:  Even if you are living in a large studio apartment, there can be hot or cool spots if the system is not balanced well.  This means that ducts take into account the distance and routing from the unit, and some dampers may be needed in order to direct the air flow more evenly.  In addition, more twists and turns in the ducts cause pressure drop, restricting air flow.  
  • Ventilated correctly:  Although this is not a requirement in the lists of Forbes and Consumer Reports, we at HypoAir argue that fresh air ventilation needs to be incorporated into any new or older system for healthy air quality.  Period.
  • Be efficient: Electric costs are increasing, just like costs for everything else.  With new inverter technology, it’s possible to get the same cooling and heating capacity at less cost. 
  • Maintained easily:  Will your system require custom filters that are hard to find (especially in this age of shortages) and does the installation company also offer maintenance plans?  
  • Not be the center of attention:  I’m talking about noise!  With older units, you can sometimes hear a distinguishable knock when the compressor kicks on. Maybe the “whistle” of air through vents is distracting for our ever-increasing home time. 

If you are building a home from the ground up, these are reasonable requirements for any HVAC contractor to fulfill.  You can see a range of HVAC solutions here.  What’s more difficult is transforming an older system into a healthy system!  Here are some ways to do just that, sourced from our own customers’ problems.

  • I live in a hot, humid area, and have a 2-story house that stays too hot upstairs.  In this case, pulling in humid air from the outdoors is not an option. What can I do?  

We found a really helpful video that explained it well:  how to get the right temperatures in the right parts of the house!  https://www.youtube.com/watch?v=ufLOd4eIjsc  Basically this is a problem when you have 1 zone cooling/heating.  The part of the home where the thermostat is installed (usually downstairs, if that is where the main living space is) gets cooled to the correct temperature, but since the upstairs shares the same thermostat and heat rises, it ends up being 5 degrees or more warmer.  Here’s what you can do while keeping the existing equipment: 

  1. Insulate the attic really well, if this has not already been done.  In existing homes, blown-in insulation is an easy way to increase the insulation.
  2. Check for other leaks in your building envelope, such as windows, doors and other penetrations on exterior walls.
  3. Have an HVAC technician install a manual damper (or series of dampers) in the duct to adjust airflow.  This will route more cold air to the “zone” that is warmer, and in general is better than shutting off registers manually, which can cause too much static pressure for the air handler.   
  4. To get more fresh air into the house, we advise adding an Energy Recovery Ventilator (ERV).  See our post on Adding fresh air through the HVAC system.

If you have the option to replace equipment, variable-speed equipment can give you the opportunity to add a second zone while providing for better cooling and constant dehumidification, as well as energy savings (inverter technology uses variable speed compressors).

  • I live in the southwest, where it can get scorching hot during the daytime and cool(er) at night. How can I reduce my electricity bill?  

Whole-house fans are useful to cool down the house at night, but if you don’t have one, you can still use the principle of “stack ventilation”, or the way heat rises through your home, to your advantage.  If you have a basement, use it as the “ground floor” of your stack–that is where the coolest air is.  Close all exterior windows and doors except for a window in the top floor, and place a box fan in it facing out.  This will be the “exhaust”.  Next go down to the basement, and open a window or door–this is the “intake”.  Open interior doors between these two windows so that air can flow upward through the house.  Even if the air outside is warmer than the basement, it will be cooler by the time it exits the basement and makes its way through the house.  You can also turn on ceiling fans near stairwells to help move air.

Here are some other ideas for extremely warm climates (some from SFGate.com)

  • If your basement does not have a cold air return vent, you can have one installed. This will enable your central AC to suck cool air from the basement and circulate it throughout your home.  If your basement smells musty, you’ll want to dehumidify and tackle mold issues first.  Similarly, make sure that you don’t have high radon levels coming in through the basement, so that you’re not circulating unhealthy air.
  • If your community water laws allow it, plant bushes and bushy trees around your home (but not too close to the foundation) to provide insulation all year round.
  • Install heat reflecting film on south and/or west-facing windows (check out our post on Low-E window films).
  • Make sure your attic has working ventilation.  Heat that is trapped in the attic is like wearing a wool hat in the summer–your body heat cannot be expelled through it!  It puts a strain on your HVAC system.  Ventilation can be accomplished via a passive soffit and ridge-vent system (outside air floats up through the soffit vents and pulls hot air from the attic through the ridge vent), or an active roof vent (a fan pulls out air through the roof) or through gable vents (active with a fan or passive).    
  • Lighten up the exterior:  There are a lot of white paints on the market, even ones that claim to reject more heat than others (like InsulAdd and Rainguard Cool Coat), but according to a cnet test, they perform similarly to plain white paint, which stays close to ambient temperature.  On the other hand, a brown stucco can be 25 degrees warmer than white paint, so although dark and black exteriors are trendy right now, you will pay for them if the summer heats up!    A new paint developed at Purdue University reflects 98% of sunlight (average white paint reflects 80-90%), cooling down buildings by 19 deg F (at night).  This means that the paint and building lose more heat than they absorb!  Traditional white paints are made with titanium dioxide, which heats up by absorbing UV rays of the sun.  The new paint uses barium sulfate and reflects the heat out of the earth’s atmosphere, to deep space. (Greekreporter.com)

Photo by Moja Msanii on Unsplash

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