Replies

1. GBA Editor
   Martin Holladay | Oct 18, 2014 05:12am | #1

   Mark,
   Yes, it's possible (although not ideal) to used forced-air heating ducts for ventilation. If you contact any HRV manufacturer, or look up their installation instructions on the Web, you'll find that manufacturers provide instructions for ducting HRVs this way.

   There are three types of HRV installations: fully ducted systems, simplified systems, and exhaust-ducted systems.

   A fully ducted system is best. These systems don't share ducts with a heating system; they have dedicated ventilation ducts. These systems usually pull stale air from bathrooms, the laundry room, and in some cases the kitchen. (If an exhaust grille is located on the kitchen ceiling, it should be as far from the stove as possible. An HRV or ERV is not designed to handle smoke or grease, so range hoods should be exhausted separately.) Fresh air is typically delivered to bedrooms and the living room.

   With a fully ducted system, the fresh air is delivered exactly where the designer intended, and the stale air is being exhausted from the right locations. These systems use less energy than systems with simpler ductwork, and they are far easier to commission and balance.

   If a house already has forced-air ductwork for a heating or cooling system, it’s possible to reduce HRV installation costs by installing a system without dedicated ventilation ductwork. The least expensive approach — often called a “simplified system” — configures the HRV so that it pulls exhaust air from the main return duct of the forced-air system and dumps fresh air into the same duct a few feet downstream.

   A simplified installation will only work if there is an electrical interlock to turn on the furnace fan whenever the HRV is operating. Here’s why: if the ventilation fans operate without the furnace fan, the fresh air will be pulled backwards toward the exhaust duct — a short circuit that prevents any fresh air from entering the house.

   The main problem with a simplified installation is the huge energy penalty that comes from continuous operation of the furnace fan. Some furnace fans draw 800 watts; continuous operation of this type of fan can cost more than $900 per year (in addition to the costs associated with the operation of the HRV, estimated at $200 a year or more). If the furnace has an ECM blower — that is, a blower with an energy-efficient motor — the energy penalty of continuous fan operation is reduced but not eliminated.

   An exhaust ducted system straddles the fence between a fully ducted system and a simplified system. This type of installation has dedicated exhaust ductwork but no fresh air ductwork. (As with a simplified system, the HRV or ERV dumps the fresh air into the main return duct of the forced-air system.)

   With an exhaust ducted system, an electrical interlock between the HRV fans and the furnace fan is optional. If the fans between the two appliances are interlocked, the system suffers from the same energy penalty problem as a simplified system.

   If the fans between the two appliances aren’t interlocked, the ventilation system will use less energy than a system with interlocked fans. When the furnace is operating, fresh ventilation air will be distributed through the HVAC system’s supply ducts. But when the HRV fans are operating and the furnace isn’t, distribution get quirky, and the fresh air enters the the house through the HVAC system’s return-air grilles. While this result is peculiar, the system still ends up delivering fresh air to the house (although probably not to the bedrooms).

2. 
   jinmtvt | Oct 18, 2014 10:00am | #2

   Mark i would suggest to verify with local BC buillding office if code mandates new houses to include HRV as i believe it does in most of Canada ( it is mandatory here in Quebec since a few years ago ).

   Your builder is responsible to meet code if it is require by it.

3. 
   Richard Beyer | Oct 19, 2014 09:32pm | #3

   Selecting Ventilation Systems for Existing Homes
   Consortium for Advanced Residential Buildings
   February 2014

   http://www.nrel.gov/docs/fy14osti/61149.pdf