Whitfield Advantage II insert question

Hi Guys,

I picked up a Whitfield insert stove a couple years ago and it's been working fine, (after a little repair). The problem I'm having seems to be the thing develops a little negative pressure in the house. I drilled a 2" hole in back of the fireplace last year and hooked up ducting to the connection in back - seemed to help a little, but not what I'd hoped. I noticed the back of the unit is open and don't see any small holes in the frame where a sheet metal cover might have been originally.

Is there suppose to be sheet metal covering the back of the unit? I don't see how the fan could make enough negative pressure to draw fresh air through the 2" pipe without something sealing up this area. The hearth shroud is vented and isn't really designed to seal air from traveling from the house to the fan, and right up the chimney.

I think I have a plan of attack. Here's a thousand words:



Basically, how I think this works is negative pressure is developed in the firebox by the fan. This draws in air though the tube behind the ash box. You can see inside the hole that there is a plate with a couple tack welds blocking airflow. Or, originally thought it was blocking, but there is about a 3/16" gap on the bottom, so it's acting as a dampener for a mixing box comprised of the fresh air tube coming in from the left side of the pic and that big hole. Most of the feed air is brought into firebox by the gaps around the sensor hole.

This makes sense to me; the exhaust fan brings in a metered amount of air, too much and it blows ash all over, too little and the pellets will overload.

A couple problems I have with this:

The area on that hole for the sensor is a lot larger than the dampener for the mixing box. Was this engineered into it, or did some kid at the fab shop just decide to make the hole fit the sensor bracket instead of the sensor? Air flow takes the path of least resistance, and that hole is the least resistive - not the gap in the mixing box.

Another question is the fan arrangement. I have a high airflow fan that draws in air from the same area as the low airflow exhaust fan metering system. These aren't isolated on my unit. I believe they both draw air in from the path of least resistance - which happens to be from the inside room. It's true, there are a lot of air entry points in a house; dryer vent, bathroom fan, and all the minor gaps around doors and windows add up. No way is a little 2" fresh air vent going to be big enough to let the fans develop positive pressure inside my house the way this is now.

Today, my plan is to take that sensor off and use sheet metal to make a hole shrinker for the sensor and seal the shroud around the edges.

One nice thing about working on the stove this time of year is my wife gives me weather updates on the half hour.

Well, I enclosed the back of the unit and now have a little positive pressure in the house.