Pushing or pulling air for heat distribution?

[KarynAnne]

I've heard some reference that ppl are using fans to push cold air from a colder room towards the stove room. That seems sort of counterintuitive. Anyone tried both ways and have a preference? The stove does a great job of heating most of the basement - just not the laundry room and I'd like to get some of that heat in there while I'm working my fingers to the bone. Thanks!

 

[Jags]

I have tested both methods quite a bit. Believe it or not, moving the cold air accross the floor TOO the stove works much better than trying to move the warm air AWAY, into another room. I think this is a result of "pressure". If I have a positive displacement of air (fan pointing out of a room) the natural tendency will be that the room will try to "refill" itself, pulling the warm air in. But if I have a fan point TO a doorway, trying to force air into the room, it will try to pressurize the room by a very small amount, but enough that you will not have easy movement into and out of the room. I hope my babble makes a little sense. Try it for yourself and report back.

 

[ecfinn]

Agreed. Definitely move the cold air. Cold air is heavier and sinks to the floor. Put a fan as close to the floor as you can get and blow the cold air out of the room into the stove room. I've tried both in my place in the last month since I've been burning, and the cold air works MUCH better. I've got one of those little corner doorway fans and its basically only useful for helping to move a bit of warm air back into the room opposite the cold air getting pulled out. The only efficient way to move the warm air would be if you could put the fan directly at the ceiling as that's where the hottest air is located. Since all doorways I've seen have at least a little lip between the rooms this doesn't work so well.

Eric

 

[Gooserider]

What about when using the HVAC fan to move the air around? Right now I have almost all the registers and returns open, and I've been wondering if there would be any benefit in closing up the registers in the colder part of the house, and the returns in the hotter part so as to make the air "loop" a bit.

The furnace and blower are in the basement under the coldest end of the house for whatever that is worth. The ducts in the basement are not insulated.

Currently, I use a Thermguard to cycle the HVAC fan ~five minutes on, 15 minutes off, which does a pretty good job of getting the house temps evened out, but seems to "eat" 2-3* worth of temperature in the living room (where the stove is) for every degree it raises the average house temp.

Gooserider

 

[Jags]

Goose, I think you will find that what you are doing will even out the temps a bit, but you are also heating all the ductwork in the basement, which in turn may be the reason for your temp loss. Not uncommon at all. I will, on occasion, turn my hvac fan on for a bit also, but simply to "even" the house out.

 

[KarynAnne]

What about when using the HVAC fan to move the air around? Right now I have almost all the registers and returns open, and I've been wondering if there would be any benefit in closing up the registers in the colder part of the house, and the returns in the hotter part so as to make the air "loop" a bit.

The furnace and blower are in the basement under the coldest end of the house for whatever that is worth. The ducts in the basement are not insulated.

Currently, I use a Thermguard to cycle the HVAC fan ~five minutes on, 15 minutes off, which does a pretty good job of getting the house temps evened out, but seems to "eat" 2-3* worth of temperature in the living room (where the stove is) for every degree it raises the average house temp.

Gooserider

I've wanted to try the furnace fan blowing. It seems like it would work well - except that there are no cold air returns anywhere near the stove. Only warm air vents in that room, and only one of those. We're installing vent free logs in the upstairs fireplace that kick out 34,000 btu's to suplement what the stove is doing from the basement. With as small as the house is, and since I don't want much of any heat on the bedroom floor that should work great. When the logs are installed there will be cold air returns in places that would make sense to try to move the air around - we'll see how that goes. I love not using the oil. The tank is 3/4 full and I hope it stays that way.

 

[KarynAnne]

Ok - I've got the fan on the floor blowing out of the laundry and into the stove room. Thanks!

 

[nshif]

I went one step farther. after seeing that pulling cold air out of the back bedroom and blowing it to the stove room greatly improved things I installed a cold air return duct from the BR to just beside the stove. I installed a low volume fan in the duct wired to a wall mounted switch which sucks the cold air from the BR and blows it out at the stove. Works GREAT. Probably increased the temp in that room by at least 5-7 degrees.

 

[elkimmeg]

I have posted on his subject weekly. It amazes me that HVAC returns are used for removing cold air There locations should be condusive to do such. As for placing a fuel burning appliance near a return ther are codes the require a prescribed separation distance. Been all threw it before and posted the codes, no more than a month back during a discussion with mike wilson

 

[Gooserider]

OK, well in our house, the returns are primarily in the BR and kitchen / dining areas that are farthest from the stove, and closest to the furnace. There are at least 3 registers in the living room where the stove is.

It makes a certain amount of sense to me that if I block the returns in the living room and close at least some of the outlet registers in the BR and bathroom areas then I would be setting up a loop of sorts that would be pulling the coldest air into the HVAC system - thus heating the ductwork the least - and encouraging the warm air to flow through the rooms, W/O going into the ducts.

Seems like it can't hurt to try.

Gooserider

 

[Mo Heat]

... We're installing vent free logs in the upstairs fireplace that kick out 34,000 btu's to suplement what the stove is doing from the basement. With as small as the house is, ...

Be careful. The general consensus is that vent free logs are for ambiance and not heating. They should be burned only a few hours a day. There are also potential issues with exhaust gases in a small house, soot if the burners get dirty or flames aren't ideal, and probably some other things I've forgotten. Many of the pros who post here don't care for ventless anything.

There have been many discussions of ventless over the last couple years. You can probably do a search if you are concerned. Be sure and buy a CO detector if you don't have one for that room.

 

[Czech]

Karyn, if you need to be convinced, tape some strips of paper to the top of the doorway. In most cases of 'pushing', you'll see the strips (and heat) draft into where you want it to go.

 

[KarynAnne]

Fan Report:

Put fan on the floor in the doorway of the cold laundry room blowing out into the stove room. No kidding - 5 minutes later you could tell a big, big difference in the laundry room.

You guys rock!

 

[Czech]

We know.....

Just don't tell us too often, esp Dylan.

 

[iceman]

does this work with pellet stoves as well????
curious to know because if a pellet stove draws its own air ........(when not connected to an outside air kit) from the area its in
will putting a fan on the floor somewhere else promote better airflow?

 

[Mike Wilson]

I have posted on his subject weekly. It amazes me that HVAC returns are used for removing cold air There locations should be condusive to do such. As for placing a fuel burning appliance near a return ther are codes the require a prescribed separation distance. Been all threw it before and posted the codes, no more than a month back during a discussion with mike wilson

Yep, we've been back and forth on this, and putting the code issues on which we disagree aside, the common consensus here is that using an HVAC system to move warm air from a stove just does not work. I have tried it using my Honeywell controllers on intermittant circulate mode, and the overall result is that you will LOSE heat in the process. My gut feeling is that you lose heat by heating up the HVAC ducts, which then immediately cool down again when the fan is off... you also lose heat by the everpresent air leaks in the HVAC system, so in effect you are heating up your basement. Much better way to do this is to simply let natural convection take place, or just put a small fan on the floor. Remember, these are space heaters, and unless you have an open floor plan, there is only so much you can do... and much of that is based on the location of the stove.

-- Mike

 

[rouxzy]

I've tinkered with the process of moving cold or hot air around the house. The best way is to move the cold air out and move warm air in. That is exactly what a furnace does. I was trying for years to get warm air around to different places in the house. The problem is when you try to move air, wheather it be cold or hot, into another area you are changing air pressures. The secret to efficiently do it is push and pull to get that circular motion of air. A fan on the floor will move the colder air but if you put another fan say high in a door way blowing air against the direction of the fan on the floor that in turn will move the warm air therefore keeping the pressures equal. One fan will do it but two fans will work quite nicely especially if you have a large area.
I have my stove in the cellar and at first I just had fans blowing up the stairs to heat the house. This did not work very well. As soon as I installed a simple air return from the far end of the house, the air moved really nice and heated up the house quickly. The cold air replaced the warm air in the cellar and the heated air replace the cool air in the upstairs.
Tom

 

[redhotz]

I have an old house with no cold air returns, the natural gas furnace just has a 16"x25 open filter. My Napoleon 1400 wood burner is in a cathedral ceiling room on the other side of the house. The bedrooms are, of course, at the other side of the house. I am thinking of pulling cold air from the basement into the wood stove room using a 6" in-line fan with 6" flex-duct. I can hook it up to a cold air register that I will install. Would pulling cold air from the basement cause the cold air in the house to flow into the basement faster and replace it with warmer air?

 

[Lumber-Jack]

I have posted on his subject weekly. It amazes me that HVAC returns are used for removing cold air There locations should be condusive to do such. As for placing a fuel burning appliance near a return ther are codes the require a prescribed separation distance. Been all threw it before and posted the codes, no more than a month back during a discussion with mike wilson

Yep, we've been back and forth on this, and putting the code issues on which we disagree aside, the common consensus here is that using an HVAC system to move warm air from a stove just does not work. I have tried it using my Honeywell controllers on intermittant circulate mode, and the overall result is that you will LOSE heat in the process. My gut feeling is that you lose heat by heating up the HVAC ducts, which then immediately cool down again when the fan is off... you also lose heat by the everpresent air leaks in the HVAC system, so in effect you are heating up your basement. Much better way to do this is to simply let natural convection take place, or just put a small fan on the floor. Remember, these are space heaters, and unless you have an open floor plan, there is only so much you can do... and much of that is based on the location of the stove.

-- Mike

Actually it does work for some people.
You make many assumptions that don't always apply. First of all heating a basement is not always a bad thing, many people actually use their basements as living spaces. In my case I have a crawl space, and yes I'm sure I lose a certain amount of heat down there through air leaks, but my crawl space is insulated and any heat lose through leaks (or warming of the ducts) helps to warm my tile floors.
Second point, which relates to the first, when you heat ducting the heat is not lost unless the duct happen to run through some area that is outside the insulated envelope of your home. Ducts are not black holes, if you heat them above the ambient room temperature they will radiate that heat back to the home as they cool down. The heat energy does not simply get consumed and lost in the metal somehow.

 

[Flatbedford]

Any body have a recommendation on a nice QUIET fan to set on the floor? The one we use, while effective, is pretty noisy even on the lowest setting.

 

[Jags]

Any body have a recommendation on a nice QUIET fan to set on the floor? The one we use, while effective, is pretty noisy even on the lowest setting.

Get one of those cylindrical ones. They are a squirrel cage design, fairly quite, yet even on low will move quite a volume of air. Not to mention the small foot print. I literally have one behind my couch, strategically placed for air movement. Something like this:

 

[roddy]

okay..i get the fan from cold room to stove room...now ceiling fans...is it fan upwards or blowing air downwards,both seem to have merits and the more i think about it,the more i can make arguments for both(huh????)

 

[pyper]

I have posted on his subject weekly. It amazes me that HVAC returns are used for removing cold air There locations should be condusive to do such. As for placing a fuel burning appliance near a return ther are codes the require a prescribed separation distance. Been all threw it before and posted the codes, no more than a month back during a discussion with mike wilson

Yep, we've been back and forth on this, and putting the code issues on which we disagree aside, the common consensus here is that using an HVAC system to move warm air from a stove just does not work. I have tried it using my Honeywell controllers on intermittant circulate mode, and the overall result is that you will LOSE heat in the process. My gut feeling is that you lose heat by heating up the HVAC ducts, which then immediately cool down again when the fan is off... you also lose heat by the everpresent air leaks in the HVAC system, so in effect you are heating up your basement. Much better way to do this is to simply let natural convection take place, or just put a small fan on the floor. Remember, these are space heaters, and unless you have an open floor plan, there is only so much you can do... and much of that is based on the location of the stove.

-- Mike

Actually it does work for some people.

It works for me too. Not really well, but it works. I can easily get a 30F heat differential between the warmest room and the coolest. I get a 10F heat drop through the ducts. It's still enough to warm the cold rooms appreciably (say 53F to 60F).

Here's my floorplan (not to scale):

The return is in the room with the stove, on the other side (blue box is return, red star is stove). As you can see, the house is not well set up for heating with wood. I have experimented with putting a fan in the room, up high, blowing air out, and also in the left-right hallway, blowing cool air in. I find that blowing the hot air out works marginally better for what I want. It makes the rooms in the upper left warmer. Blowing cool air into the room makes the room on the bottom warmer, but it's already warmer and I really want to warm the rooms in the upper left.

I believe I'm going to put a hole through the return. I will probably draw warm air into the cold room. That will create positive pressure in the cold room which will cause air to circulate around the house in a big circle. Since that room in the upper middle is the coldest and since the room off on the middle left doesn't need heat, I think it will make more sense to circulate heat counter-clockwise than to circulate clockwise.

I think I'll put a hole in the top of the return (it's about 30" from the floor) and mount a bathroom exhaust fan into the return. With the light removed and no duct attached it should move at least 100 CF per minute. I think I'll also need to remove the return filter to avoid just sucking cold air from the return ducts. Which means I'll need to remember to put it back! I'll also need to seal the blower when it's not blowing, so that dust isn't drawn into the return.

The room with the stove has two ceiling fans, so the air is fairly uniform in temperature, floor to ceiling. I have noticed that the fan on the left, if set to blow "down", will push hot air off the ceiling and into the next space. Set to blow "up" it does not do that.

Fluid dynamics (moving air) is a complicated science. There are a lot of variables and no single solution will work for everyone. Fortunately, most of these things are easy enough to experiment with. Run the ceiling fan both ways and see which works best. Same thing for box fans. Just try it out, and then you'll know what works in your house. Cutting into duct work is a little less easy to experiment with, but sheet metal is easy enough to repair. If it works the payback will be tremendous, and if it doesn't work it will just cost a few sheet metal screws and some tape.

One thing to keep in mind is that heat radiates, and cold does not (fact of physics). If I leave the door open to the room in the upper right, the room in the middle will warm too, because the heat in the room will radiate through the wall into the cold room. It's an appreciable difference, too.

 

[John_M]

roddy, My house has two ceiling fans in the stove room located at the back of the house. The ceiling there is 13'. My effort is to get some warm air to the bedrooms at the front of the house. I have tried numerous combinations of ceiling and floor fans pushing and pulling air from all directions using different speeds.

What works best in my floor plan is to use only the ceiling fans. The fan near the stove is pushing air up to the ceiling at a moderate speed. The fan at the other end of the stove room is above the entrance to the hallway leading to the bedrooms. This fan is set at low speed blowing air down. It seems this fan blowing down creats an upside-down mushroom shaped warm air flow that slowly works its way to the bedroom area. Setting this same fan blowing down at a moderate speed creates enough wind that it has more of a cooling effect. At least that is how I believe air movement works in my house.

The stove room has lots of windows. The top of the double hung window nearest the stove, about 3' away, is opened about 3/8" at the top during the daytime and during all weather. The outside air entering the house through this window is immediately heated by the stove so one does not feel any cold air in the room. I am convinced, but cannot prove, this little bit of outside air entering the house allows a slight exchange of outside/inside air during the day and this benefits my breathing.

It appears to me that, after reading most of the threads about this subject, every house is just enough different from the others that there is no "one size fits all" answer to the movement of warm air to cooler areas of the house.

Good luck with your experimenting.

John_M

 

[pyper]

Oh, here's something else I found out about my house:

In the upper left of my house is a bathroom. It has a high powered exhaust vent. If I run that vent it will draw warm air towards it -- through the house.

That middle left room (on the floorplan posted previously) will be noticibly warmer. Interesting, it's only warmer in a line between the doors -- if you go off into the other side of the room it's just as cool as it had been.

I suspect I could really heat the back of the house if I simply opened a window and put a box fan in it, blowing air out of the house (which would quickly pull warm air from the stove room if I cracked a window near the stove). Something just feels wrong about wasting so much heat.