Replies

1. Expert Member
   MALCOLM TAYLOR | May 25, 2021 07:26pm | #1

   CueCT,

   Ventilation is measured in cubic feet per minute, in other words by how much air you bring in, not how many minutes your system is on for.

   The guidelines for how much air can be found in this article: https://www.greenbuildingadvisor.com/article/revisiting-ventilation

   The amount of air needed is determined by how much is necessary for human health, so it is important that it doesn't get turned off when conditions are humid or cold.

1. 
   suect | May 25, 2021 08:28pm | #2

   Thanks for the article. From what I read, my home is 2500 sq ft fresh air is at 60 cfm, I have a 3 bedroom home so basically 24/7. Is there concerns about too much positive pressure?

   We have an AprilAire system with a motorized fresh air intake. At this point an ERV is not possible. Would bath fans at 10 min per hour be of help?

2. Expert Member
   MALCOLM TAYLOR | May 25, 2021 10:05pm | #3

   SueCT,

   Here is what Martin wrote about supply 0nly systems:

   "Some builders worry that a supply-only ventilation system (for example, central-fan-integrated supply ventilation) won’t work in a cold climate, because the ventilation fan will drive interior air into building cavities where moisture can condense.

   This worry is needless. As energy expert Bruce Harley explains, “The upper portions (walls and ceilings) of every home — typically most of the second floor in two-story homes — already operate under positive air pressure in cold weather, due to the stack effect. The relatively small airflow of most supply-only ventilation systems (75 cfm to 150 cfm) will have little effect on this situation other than to shift the neutral pressure plane down slightly, in all but the very tightest of homes. … In cold climates, I believe that distributed, supply-only ventilation such as that supplied by a ducted distribution system controlled by an AirCycler, or other ducted low-flow supply ventilation, is vastly preferable to single or multi-port exhaust-only systems, except in extremely tight homes (in which case balanced supply and exhaust ventilation is the best choice).”