Replies

1. 
   JWXNMHqdgg | Jul 25, 2011 03:32pm | #1

   I had the same reservations when I installed one several years ago, which was the only time I've worked with a Fantech unit. I wound up running a separate supply system to the bedrooms to try and stimulate air movement which worked fairly well. We did have plenty of space for ductwork although it was a bit more labor intensive. I do wonder if the Fantech unit could push enough air through the air handler when it's not running? Possibly you could run the supply into the air handler and have someone do some pressure checks to see if that works, and if not, go ahead and wire up the air handler to come on with the ERV.

2. GBA Editor
   Martin Holladay | Jul 25, 2011 03:44pm | #2

   John,
   If you hook up the ERV's fresh-air supply duct to your furnace's cold air return, you'll have to wire the furnace's blower to come on when the ERV is operating. This incurs an enormous energy penalty.

   That's why I have always advocated installing dedicated ventilation ductwork for any HRV or ERV. Furnace ductwork is much too large for ventilation air distribution, and the fresh air will never reach remote rooms without the furnace fan operating.

   Read more here: Designing a Good Ventilation System.

3. 
   Faulted1 | Jul 25, 2011 03:52pm | #3

   Martin,
   You state flatly:
   "you'll have to wire the furnace's blower to come on when the ERV is operating. "

   The instruction manual states:
   ""Furnace blower may be required to operate..."

   Any explanation for the apparent difference?

4. GBA Editor
   Martin Holladay | Jul 25, 2011 05:02pm | #4

   John,
   Well, if your furnace ducts are perfectly tight, and have an unusually small diameter, and are very short, it might work.

5. 
   user-626934 | Jul 26, 2011 01:03pm | #5

   Martin,

   I'm with you on air-tight ducts and short runs...However, how would "unusually small diameter" ducts help?

6. GBA Editor
   Martin Holladay | Jul 26, 2011 01:35pm | #6

   John,
   OK, you might be right.

   Ventilation ducts are usually 4-inch diameter ducts. Sometimes they are 6-inch diameter.

   Furnace ducts start out big -- 8x24 isn't unusual. A furnace has a big fat plenum with cracks and leaks between the furnace and the plenum. When you blow ventilation air into a plenum, where does it go? The pressure is greatest in the plenum -- generally the leakiest part of the duct system. The ventilation air never makes it to the ducts, really. Perhaps it makes it to the first few leaky joints in the 8x24 main duct.

   What you want, ideally, is a small, tight, duct system dedicated to your ventilation system.