The latest “Houses” issue (no. 195) has an article titled “My Mountain Bungalow” where the author talks about an anti-stratification system used in the house to keep the basement and other floors near the same temperature. This sounds like a toned down geothermal system.
I’ve not heard about this type of system before. Anyone have any additional info or pointers to more info?
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Replies
Sounds to me like they're referring to what is technically known as a "fan".
I Dan deserves an award here....
"Sounds to me like they're referring to what is technically known as a "fan"."
That's what I got out of it too. Just a duct with a fan to pump hot air down to the cold basement and vice versa.
Mike HennessyPittsburgh, PA
With a forced air system it can be incorporated for virtually no cost. Assuming you have a single air handler unit, you could install dampers on both supply and return so that supply goes upstairs and return comes from downstairs, eg. Maybe switch the other way every 15 minutes. Even without the dampers a common air handler will mix the air significantly, reducing stratification.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
Yeah, but you gotta be careful if you're drawing air from the basement (or, more precisely, from an area near the flue) so you don't create a down-draft if you have a traditionally vented unit. Or so I've been told.
Mike Hennessy
MY MIL has a very cold basement in the summer. Absolutely no returns within that area. Several supplies which are closed off. Still cold.
Would installing a return (closeable) into the return trunk close to the air handler be a solution? Then shut the return in the winter.
If she's running the AC then likely it's cold because of leakage from the ductwork, and that needs to be sealed. Otherwise the return air duct would help.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
McDesign did a cool "anti-stratification" sock for a relative recently. Was used to pull the hot air from a loft down to the first level (in Winter) I'll see if I can find that thread.
Found McDesign's sock on a search:
98162.1
Edit to fix link.
Edited 5/11/2008 8:46 pm ET by NatW
If a forced air system is used a variable speed air handler will do just that. It runs occationally at a slow speed controled with an inexpensive programable thermostat and like magic will even out air temps!
Many people don't realize their current system will do just that because they won't read the manuals for their HVAC equipment.
For a non-forced air system, small ducts connected to a whole house ventilation system and air filtration system will do the same.
At the most basic level a $100 Fantec remote fan and a few hundred in 4" ducts will move air from one part of the house to another.
Beer was created so carpenters wouldn't rule the world.
Yeah, I got that it was a fan. So I guess I'm asking if this is really a worthwhile investment of time and small money to install. We've got FHW baseboards so it'd mean installing a duct and fan. I would need a return duct too, right? Does it make a big difference in heating and cooling costs? Seems like it would be more of a big deal if it helped as much as the author indicates - not stuck in a sidebar of the article.
If you have an open stairway you specifically DON'T want a return duct. You use the stairway for the return and the air gets distributed more broadly than if it went from one duct to the other.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
Often the benefit from an air circulation system is more related to comfort than pure cost savings.
Of course if you have a hot room upstairs and a cool basement it makes more sense to take advantage of that temp. differential.
Beer was created so carpenters wouldn't rule the world.
It will help even out temps ... but only if you have stratification problems. Not all houses/situations mean there is stratification. Measure the air temps in the various locations. A 20 deg difference is definately stratified ... I've measured that much. But I've also measured it in a house w/ 15+ ft ceilings ... with very little stratification.
If you have a cold basement and a warm upstairs and this is uncomfortable, the fan/ducts will work great. It's simple.
Will it save money? Probably, but again, it depends. If you keep the basement at e.g. 70 deg and as a result, the upstairs is 85 deg, your average temp is about 77 deg. During heating, this increases heat loss substantially (heat loss is linear with the difference of indoor/outdoor temp).
If the basement is e.g. 60 deg and upstairs is 70-72 and you are trying to achieve comfort ... it won't save you energy ... maybe even cost a little more. But, if comfort is important ... you need to set the energy cost aside.
In the summer you can reverse the concept and use cooler basement air to temper the upstairs ... assuming you are opposed to escaping the heat by going to the basement.
You shouldn't have to run the fan real frequently ... you could even tie it to a thermostat in the basement to kick off once the set point is reached.
Remember the fan will cost $ to run ... but it's probably 1/4 to 1/2 HP ... so no real big deal, but it ain't free, either.
An anti-stratification fan will work in a well-insulated house. The problem is, most basements aren't well-insulated or sealed up at the bottom plate.If this detail has been done well, and the attic and walls are well-insulated, the stratification problem isn't very bad in the first place.I've tried it in many homes, and it just doesn't solve the problem. Surprisingly, it didn't even help.
Not sure why you say only works in a well insulated house. Something doesn't sound right. The concept and application is simple ... if the air temp is not balanced, install and air crculator to balance it. If one area is not well insulated, it shouldn't really make much of a difference ... the fan may run longer or take longer to destratify, but it should work. Maybe your fan wasn't big enough? Maybe the duct in the basement didn't suck off the floor? Maybe you didn't have a return air system? An imbalance of insulation should not affect the concept.
I would run the forced air heating (fan only) on a cold day to see if the temperatures would even out. I could start with 70F upstairs and 64F downstairs. After 6 hrs., not even one degree of equalization would occur.Theoretically, there should be some equalization. In practice, there was none. It was probably due to a combination of many factors. Higher air leakage in the basement, uninsulated concrete walls in the basement, more lighting and electrical usage upstairs, warm people upstairs, better windows upstairs, etc. Part of the conclusion is that you can't move much heat by blowing 600CFM of 70F air into a 64F space. The insulation in my new house has a high R-value and was detailed well. I don't have any stratification, even with the heat off for days on end in cold weather. My conclusion: the heat loss from the basement is somewhat lower per square foot than upstairs. The basement therefore would actually be warmer than upstairs, except that natural convection in the stairway transfers heat up and keeps the house isothermal. (the Manual J calculations show the basement heat loss at half as much per sq. ft.)
If your furnace returns air from both levels and supplies them to both levels ... at the floor level upstairs and the ceiling level downstairs (the conventional configuration), you've got some issues. The return/mixed air temp will be 67 degrees ... not much of a difference. You may not be blowing 70 deg air into that space downstairs. 600 CFM isn't much air flow either. Your 6 degrees of stratification isn't much. And you supply it at the ceiling in the basement?
While the DESIGN heat loss in the basement may be very small, a floor slab has a lot of mass that will tend to not allow that space temp to necessarily fluctuate too much. Especially over a 6 hour period.
You have low temp stratification. I don't know your duct configuration, but if you want to warm your basement a bit more, give it more air ... i.e. balance the system a bit to compensate for the difference in construction and balance the temps in the house.
It can get complex fast. Like you said, lots of factors can alter a simple concept.
For high temp stratification, it's best to pull air from up high and supply it back down low to maximize the mixing.
I talked to my SIL yesterday; she ran the heat-sock anti-stratification deal I made for her ALL WINTER, continuously, and it dropped her gas bill, didn't raise her electric bill, and made it a LOT more comfortable down at her 5' level.
Forrest