Too bad we can't see air currents. I think about this topic quite a bit, as I find it interesting--almost game-like to try to optimize this. Ran into an interesting problem (if you're wired to find this interesting, that is) this week.
My house circulates air pretty well, and the heat from my stove downstairs heats the upstairs pretty thoroughly, especially centrally. The stove is centrally located, and there are no lintels between the stove and the staircase in which the heat is funneled upstairs. The staircase head space at the bottom is sloped to follow the angle of the steps on a twisty landing at the bottom, then it's a straight shot up which has created a `heat reservoir' from which heat is drawn into the upstairs. The stairs run parallel with the length of the house, between an outside wall on the north, and (upstairs) a bathroom. At the head of the stairs, you can turn right and go outside, or left and enter a short corridor. Bathroom door opens into this corridor on the left, a bedroom is to the right. The corrior opens into a family room, with another bedroom on the right. Turn left, go through the family room, and there's a door into the master bedroom. Turn left again, into a small bath, pass through it, and you're in that first bathroom, go through that and out into the corridor again.
I thought that the circular passage of air through these rooms was the engine that drove the air circulation upstairs, drawing off heat as it passed near that heat reservoir. Since the master bedroom doesn't get whole-room air movement, it's not one of the warmer rooms in the house. I recently (inspired by a few threads here) decided to use the built-in-but-never-utilized HRV ducting to improve upon this. This house was built back in '84, so the builder was semi-brilliant to even consider an HRV at that time, but the ducting he put in is only 4" ducting.
Ducting has, as far as I can tell, only four outlets: one in each of the south bedrooms upstairs, one in the laundry closet upstairs, and one in the ceiling of the dining room, which is adjacent to the wood stove. I believe that all of these runs of duct converge in one place in the ceiling downstairs.
Was considering a fan purchase when I remembered that the PO left behind a few new-in-old-boxes fans designed to move air from ceiling to floor in a stud bay, "whisper quiet motor", adjustable from 20-108 cfm. Heck, may as well use these as buy more.
Started fiddling with the plenum in the floor of my bedroom (at the far end from the doors where the `Great Current' circulates) into which the ducting is piped to see if these fans would fit. I never gave it any thought about the ducting functioning in a passive state, but I was surprised to a) feel a definite air current moving, and b) to feel that it was pulling the colder air from my bedroom down into the ducting.
This did not make sense to me, because I am Newtonian to the core, and happily hold fast to the `warm air rises' principle, even when it's wrong. After chewing this over few a few days, concluded that along with the circulation on the horizontal plane (through all those doors, driven by the temperature differential), I also have circulation going on between floors through this ducting.
I played around a little last night with incense and a flashlight, and there is no doubt that air is being pulled rather briskly through the ducting in both bedrooms (master and the other one situated off family room in the southwest corner), upwards (again, I was surprised) through the ducting in the laundry closet (off the family room, sharing a wall with that first bathroom I mentioned). The other opening of the ducting that I'm sure about is in the ceiling of the hearthroom, about 8 feet from the woodstove. It seemed to me that the cold air was being pushed down through that, although it was harder to tell (hadn't gotten the flashlight at that point).
Finally concluded that Newton is still right, and that this circulation in the ducting was a result of pressure differential--that the heat movement upstairs was so much stronger that it pulled cool air down through the ducting.
If I install this fan, it means modifications to the plenum, so I want to think this through before I act. Another option is tearing out sheetrock in the ceiling of the pantry (no big deal, it's raw) until I find the junction boxes where all the ducting comes together--at least, I think it's in the pantry---and putting a fan in there that would support rather than fight the existing air flow current.
So my question, assuming that someone has actually slogged this far through this post, is about the wisdom of putting those fans in the bedrooms as I had planned. I had intended to put them in so that they pulled air from the hearthroom upstairs into the bedrooms. Advantage would be to have the fan, with controls, at point of use. Now I'm concerned that this will be like trying to halt and reverse a system that is actually working pretty well already (usually a two-degree temp diff between upstairs and downstairs, as measured by a thermometer located at shoulder height right on the path of that central air flow) to heat most of the upstairs in hopes of making an off-the-vortices corner cozier.
Or, I may be seriously overthinking this whole thing and am grasping at pathetic straws to linger inside a little longer instead of going out to chop that wood in my driveway. Seriously, though, I would appreciate any wisdom/experience anyone has to share.
My house circulates air pretty well, and the heat from my stove downstairs heats the upstairs pretty thoroughly, especially centrally. The stove is centrally located, and there are no lintels between the stove and the staircase in which the heat is funneled upstairs. The staircase head space at the bottom is sloped to follow the angle of the steps on a twisty landing at the bottom, then it's a straight shot up which has created a `heat reservoir' from which heat is drawn into the upstairs. The stairs run parallel with the length of the house, between an outside wall on the north, and (upstairs) a bathroom. At the head of the stairs, you can turn right and go outside, or left and enter a short corridor. Bathroom door opens into this corridor on the left, a bedroom is to the right. The corrior opens into a family room, with another bedroom on the right. Turn left, go through the family room, and there's a door into the master bedroom. Turn left again, into a small bath, pass through it, and you're in that first bathroom, go through that and out into the corridor again.
I thought that the circular passage of air through these rooms was the engine that drove the air circulation upstairs, drawing off heat as it passed near that heat reservoir. Since the master bedroom doesn't get whole-room air movement, it's not one of the warmer rooms in the house. I recently (inspired by a few threads here) decided to use the built-in-but-never-utilized HRV ducting to improve upon this. This house was built back in '84, so the builder was semi-brilliant to even consider an HRV at that time, but the ducting he put in is only 4" ducting.
Ducting has, as far as I can tell, only four outlets: one in each of the south bedrooms upstairs, one in the laundry closet upstairs, and one in the ceiling of the dining room, which is adjacent to the wood stove. I believe that all of these runs of duct converge in one place in the ceiling downstairs.
Was considering a fan purchase when I remembered that the PO left behind a few new-in-old-boxes fans designed to move air from ceiling to floor in a stud bay, "whisper quiet motor", adjustable from 20-108 cfm. Heck, may as well use these as buy more.
Started fiddling with the plenum in the floor of my bedroom (at the far end from the doors where the `Great Current' circulates) into which the ducting is piped to see if these fans would fit. I never gave it any thought about the ducting functioning in a passive state, but I was surprised to a) feel a definite air current moving, and b) to feel that it was pulling the colder air from my bedroom down into the ducting.
This did not make sense to me, because I am Newtonian to the core, and happily hold fast to the `warm air rises' principle, even when it's wrong. After chewing this over few a few days, concluded that along with the circulation on the horizontal plane (through all those doors, driven by the temperature differential), I also have circulation going on between floors through this ducting.
I played around a little last night with incense and a flashlight, and there is no doubt that air is being pulled rather briskly through the ducting in both bedrooms (master and the other one situated off family room in the southwest corner), upwards (again, I was surprised) through the ducting in the laundry closet (off the family room, sharing a wall with that first bathroom I mentioned). The other opening of the ducting that I'm sure about is in the ceiling of the hearthroom, about 8 feet from the woodstove. It seemed to me that the cold air was being pushed down through that, although it was harder to tell (hadn't gotten the flashlight at that point).
Finally concluded that Newton is still right, and that this circulation in the ducting was a result of pressure differential--that the heat movement upstairs was so much stronger that it pulled cool air down through the ducting.
If I install this fan, it means modifications to the plenum, so I want to think this through before I act. Another option is tearing out sheetrock in the ceiling of the pantry (no big deal, it's raw) until I find the junction boxes where all the ducting comes together--at least, I think it's in the pantry---and putting a fan in there that would support rather than fight the existing air flow current.
So my question, assuming that someone has actually slogged this far through this post, is about the wisdom of putting those fans in the bedrooms as I had planned. I had intended to put them in so that they pulled air from the hearthroom upstairs into the bedrooms. Advantage would be to have the fan, with controls, at point of use. Now I'm concerned that this will be like trying to halt and reverse a system that is actually working pretty well already (usually a two-degree temp diff between upstairs and downstairs, as measured by a thermometer located at shoulder height right on the path of that central air flow) to heat most of the upstairs in hopes of making an off-the-vortices corner cozier.
Or, I may be seriously overthinking this whole thing and am grasping at pathetic straws to linger inside a little longer instead of going out to chop that wood in my driveway. Seriously, though, I would appreciate any wisdom/experience anyone has to share.
