Anyone ever install this in-duct fan? Need your input HVAC guys

Dune · Oct 23, 2010

repost.

Dune · Oct 23, 2010

fdegree said:

I agree with Dan...trying to move cool air up and warm down is not likely to happen naturally.

Putting box fans on the floor is an entirely different situation. What I'm going to discuss here is what seems to be the topic at hand...fans with ductwork attached.

Now, my specialty is with traditional HVAC equipment, so this concept of simply moving air to accomplish a certain heating task is a little different than I'm use to dealing with. I will try to give my thoughts on the matter, but keep in mind, I may overlook something.

The way I see it, there are 2 options:
1. Pull warm air from above the stove and dump it in the desired location
2. Pull cool air from the floor level of the desired location and dump it near the stove

I would think that option 1 will be the most efficient. Why? Well, we must look at option 2 for the answer:
If you pull air out a room, that air must be replaced with air from someplace else...the "replacement" air will come from the least restrictive path...if that is through leaks around windows/doors/etc., you could be pulling cold, outside air into the room you are trying to heat. Granted, the stove room will become pressurized, and some, not all, of that heat will migrate to the lower pressured room. But, if you have a leaky home, some of that heat will be pushed out through leaks around windows/doors/etc. in the stove room. Also, if the wind is blowing outside, what room is the wind hitting first...if it is the room you are trying to heat, then your "replacement" air will come from outside more easily.

With option 1, you are pulling warm air directly from around the stove and dumping into the room that needs the heat...there is no question where that warm is going to end up.

I hope this helps...if not keep firing away...I'll do my best to answer what I can.

It is well established that option 2 works, while option 1 doesn't. 1 doesn't work because the delta T is too low.

Option 2 works for the reasons you mentioned, negative pressure in the far room, positive in the stove room, the path of least resistance is the "return", the open doorway through which the warm air passes, thereby following the laws of thermodynamics.

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Anyone ever install this in-duct fan? Need your input HVAC guys

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Anyone ever install this in-duct fan? Need your input HVAC guys

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