Quote:
Originally Posted by Dan Foss
1. Do i really need the Combustion air intake if i already have a air exchanger drawing fresh outside air? (would love to seal it if i dont)
2. where would the exchanger draw air from inside the house?
3. The draw from combustion intale while the furnace is not running also makes me think potential negative pressure in the basement? but really wouldn't i only see the negative pressure while the furnace runs and shortly after?
.
|
1: Yes,,you still need a combustion air. If you get new direct-vent appliances their combustion air supplies can be piped directly to each appliance through independent pipes from outside. This eliminates the cold draft from the combustion air bucket that got superseded.
2: An HRV can draw air from the furnace return air or it can have independent ducts running to rooms such as a kitchen or bathroom that require more airflow.
3: Just because your appliances are not firing doesn’t mean your chimney isn’t drawing heat out of your home. Natural draft appliances such as an older furnace will always have air flowing up the chimney. Idle conventional water heaters will have a greater chimney draft than the furnace because the heat exchange pipe through the tank itself is surrounded by hot water, that hot water heats the air and creates a much stronger draft than a furnace that has cooled off; this effect of course cools the water and will prompt the tank to fire once it has shed enough temperature. This chimney effect is a primary component of what we call ‘standby loss’, though there are other sources such as the small amount of heat lost through the water heaters insulation jacket, etc (though conversely, at least that standby heat loss is shed into the house). Direct vent appliances that have their own dedicated combustion air piped right to them save utility costs by drastically reducing standby losses through the chimney. A pair of intake and exhaust pipes to a direct vent appliance will generally be installed at the same level (or reasonably close) and as a result will have either no or very little natural chimney effect occurring.