"Moving Heat" : Convection Air Currents in Your House

[becasunshine]

There are numerous discussion threads on this forum about moving heat from one room to the next when using our wood burning appliances.

We have a 1410 sq ft bungalow with a circular floor plan. The stove is literally in one corner of the house.

Our first couple of seasons with our pellet stove were less than satisfying. We'd been told that the stove would run us out of this house. Didn't happen- not the first year, nor the second year- not until we got a lot more serious about our insulation. (That's a whole other thread.)

Turns out that the first couple of years, our problem really wasn't moving the heat around- it was keeping the heat in the house. Insulation has helped a lot.

On colder nights we will put a box fan on the floor in the room with the stove, aimed at the stove, to facilitate and augment the natural convection currents. The box fan pulls cold air along the floor from the rest of the house into the stove room, and this displacement of air pushes warm air out of the top of the room and into the rest of the house. We believe that this works- we can feel the heat rolling out of that room, and we can feel the other end of the house warm up.

Sometimes, if we are sitting in the living room (the stove is in another room) the air displacement from the box fan is noticeable. It feels cooler while sitting down in the living room, because the cool air is moving past us quickly.

It's pretty chilly here tonight, it's 28'F outside right now. We are burning Turman's this evening. The stove room is holding at 72.5'F. The rest of the house is holding at 67'F. (We normally keep the gas furnace set at 65'F so this is a warmer temp than we'd pay to run the gas furnace.)

Tonight, for some reason, it finally occured to me to do the toilet paper test. I just took a roll of toilet paper and a roll of tape and taped a strip of toilet paper in the doorway of each room of the house. I turned the box fan OFF so we could see the natural convection currents.

Wow. Wow. Insane. We can *see* the air moving, and it *is* moving. A lot. NEWSFLASH: HEAT IS MOVING ITSELF THROUGH THE HOUSE ON ITS OWN. I am now more convinced than ever that the best thing we can do is hang onto the BTUs rather than trying to move them aggressively from room to room.

The air movement on its own, without the box fan assist, is pretty impressive. Gonna check it again with the box fan running, but given this visual, I'm going to leave the box fan off more than on, I think.

 

[briansol]

Try putting the fan in the far end of the cold side of the house to push cold air towards the stove.

 

[becasunshine]

Try putting the fan in the far end of the cold side of the house to push cold air towards the stove.

LOL, but then I'd be in between the cold air from the fan and the stove!

How are you, Brian? Long time no type at. Did you get your (kitchen) stove burner worked out vs. a pressure canner?

I will try the fan at the other end of the house- why not?

 

[briansol]

No, I never got that outdoor burner..... just did a lot of high acid on the water bath this year.


The idea is to get the cold air out of the corners and replaced with warm air. it should only be cold for a little while.

 

[St_Earl]

some folks (me included) do the pushing cold air toward the stove by placing the fan just outside the 'stove room" blowing in.
fan at floor level. you will feel the warm air subsequently being displaced /pushed out of the stove room.
it's somewhat surprising how much more effective it is to push the warm air out as compared to sucking it out.

i use 2 vornados up high (one aimed at the next) to shoot the warm air back toward the back bedroom along the top of the convection loop.
since the warm air is being fed to the first one in the stove room door arch, it's working to push the air where i want it too.
if it's only a little cold, we may skip the floor fan blowing in. as then the reduced performance meets the need better as we are aiming at a pretty much constant temp back there. it's easy to get it too warm for my wife.
but when it gets to zero and below, it's all fans on deck.

i'm able to regulate the temp in the back bedroom in just a few minutes this way.

just play around with it.
you'll find what works best for you and your layout.

if you could do the floor fan from all the way back, it would do the job on it's own.
we just have concerns and obstructions that make my variation on the theme work better for all our specific needs and layout.

 

[Pellet-King]

No, I never got that outdoor burner..... just did a lot of high acid on the water bath this year.


The idea is to get the cold air out of the corners and replaced with warm air. it should only be cold for a little while.

Must be a new way to get high

 

[Madcodger]

You mentioned "holding onto BTUs". Bingo! More people need to focus on this. We pay for energy production no matter how we produce it. The less we need to produce, the less we spend - period!

 

[newbieinCT]

This thread is motivating! Thank you - I needed that today...
We have to insulate and we are trying to figure out what to do (pick a company, cellulose vs foam, etc) but posts like this push me to figure it out quicker! (Well, that and the cold temps....). It's hard to spend the money on insulation but reading these posts about the difference it makes with good insulation pushes me to get it done quicker! Thank you

 

[SmokeyTheBear]

Holding onto the BTU's interesting who would have thunk of that.

If you visit the heat loss calculator at builditsolar.com you can play with the numbers one of the numbers I suggest everyone play with is the air exchange numbers. Those should scare the clothing off of most people.

 

[becasunshine]

Must be a new way to get high

We were all posting pictures of our pellet stoves burning during a particularly cold night last year. In the middle of that thread, I posted a picture entitled, "Meanwhile, at the other end of the house," showing my 22 qt. Mirro pressure canner on the stove top. (Yeah, it was throwing out some BTUs of its own.) A portion of the thread and its participants branched off into pressure canning, and stove tops, and stove types, and watts vs. joules, and the wattage of various burners, and the amount of energy needed to bring a big canner up to pressure, etc.

I tend to wander away from this forum in the summer time, so this is the first time this year, *I think*, that Brian and I have typed at each other. Brian was having a difficult time getting his stove burner to bring his pressure canner up to pressure, IIRC. We use pressure canning to put steam under pressure to achieve a higher processing temperature than can be achieved by boiling water- which by the function of turning water into steam, will never achieve a higher temperature than 212'F. Pressure canning is used to process low acid foods- foods in which acid levels are too low to mitigate the growth of bacteria and molds. We basically autoclave that food in a pressure canner to kill all the bad stuff that could cause the food to spoil.

High acid foods contain enough acid, either naturally or we add acid in the form of high acid ingredients (vinegar for instance) according to specific, approved recipes, that the acidity of the food prevents pathogens from growing in it while it's sealed in the jar. It's important to use FDA tested and approved recipes to achieve a high enough level of acidity- because one is using this chemistry to preserve the food. High acid foods can be processed in a boiling water bath- so one's stove burner simply needs to be powerful enough to boil water.

Briansol, in retrospect, we may have gotten too far into the weeds about that burner last year. If the burner is strong enough to boil water, then you should be able to bring your canner up to pressure- because basically all you are doing with the pressure canner, after it is properly vented, is boiling water to make steam but keeping a portion of that steam trapped in the canner for enough time by PARTIALLY obstructing the outlet with the appropriate weight to build up that many pounds of pressure in the canner...

... and WE'RE OFF! Herein begins the discussion of joules vs. watts vs. boiling water vs. stove burners vs. canners, 2013/2014!

 

[becasunshine]

I think that at the end of the day we will always deal with conduction cold/bridge cold in this house, with the brick/block/lathe/plaster walls. Right now the interior walls are COLD. If we had it to do over, we would have gone looking for a pellet stove that puts out more BTUs. Yes, it burns more pellets, but we really could use more heat to battle the conductive cold. I guess we could trade the Napoleon for a bigger stove... just haven't done it so far. We are working on the other side of the equation right now, hanging on to what we've got.

We can't blow insulation into these walls (at least not as far as I know) and other than working on the crawl space and/or skim coating the outside of the house (I don't know the name of the product, I just know that this was one suggestion) there's not many other places we can go with this house in terms of insulation. We have already insulated the exterior perimeter electrical outlets and switches, and that worked so well that we recently insulated the interior outlets and switches. Attic has a radiant barrier tented on the ceiling joists, original rock wool between the floor joists, R19 batting laid in between the floor joists (in good shape) and fresh R30 batting rolled out perpendicular to that. Ceiling fixtures in the house, leading to the attic, are tight.

While we can see NO WATER from this house, FEMA has redrawn the flood maps and we are now in a flood plain. =/ =/ (Long story.) FEMA would not take kindly to us sealing the crawl space. We already have R19 insulation under the floor. We are investigating ways to add more insulation without sealing the crawl and running afoul of FEMA.

In the end, should we wish to be warmer in very cold winters, it might mean swapping out for a bigger stove and burning more pellets, but we have a few more places in the house that we could fine tune, I think. A little caulk here, a little caulk there... mebbe something else we can do with the crawl space...

 

[rowerwet]

clear plastic over the windows even more modern ones helps

 

[P38X2]

Great point on NEWER windows leaking. While being "contractor" grade, the specs on the glass AND air infiltration on my windows are very good. However, through the 7 years of use, the weatherstripping has become compressed in a way it cannot rebound from. Bottom line is it's a chitty design that the company (Alliance) cut corners on to save money. Some of my windows leak air badly enough that I will have to take steps to stop it. My previous home had 25 year old Anderson windows that didn't leak air...at least not enough to be measured using a "hand" dyno. Here's a pic of a gap in one of the windows. Notice the inspiration behind NOT using a humidifier any more?
Back on topic....while using fans to assist the EXISTING natural convection currents in your home is generally the rule, DON'T assume because you identified the currents using incense smoke or TP, that is the BEST solution to moving the air. For a few seasons now, I've been blowing cold air coming down the stairs from the 2nd floor of my colonial back TOWARDS the stove. This worked very well but there was always a cold breeze blowing across the room that gets used the most. I finally got sick of this and turned the fan towards the dining room, AWAY from the stove, and it did wonders in evening out the temps throughout the house AND eliminating the cold air across the living room. The natural convection current isn't set in stone in some cases. With a little fan assistance, I was able to set up a new convection current that worked far better than the original one. Try it out if you're in a 2 story house with a staircase down the middle.

 

[jimfrompa]

Excellent discussion. This is our first year with a pellet stove and I was worried about getting the heat to the opposite side of the house as well as upstairs. The Mt. Vernon AE is at the far end of the house in the living room with the bedrooms at the opposite end. There is an open stairway to the second floor with one big room. I have my living room set at 77 with 4 degree differential. The most distant bedrooms on the first floor stay at 70 - 71 degrees. Several days ago the low here in PA was 17. The entire house was comfortable - the Mt. Vernon is rated at 50,000 BTU's. I was told by a friend that if I crack a window in the most distant part, the warm air would find that window and the whole house, in effect, would act like a chimney - said warm air always replaces cold air. I've tried it for a few minutes and did not find that it worked. Maybe I need to let it cracked longer. I will try the fan solution - pointing a floor fan towards the stove room and see if the temps in the back rooms rise.

 

[briansol]

That will just draw in more cold air...

 

[ChandlerR]

There are numerous discussion threads on this forum about moving heat from one room to the next when using our wood burning appliances.



Tonight, for some reason, it finally occured to me to do the toilet paper test. I just took a roll of toilet paper and a roll of tape and taped a strip of toilet paper in the doorway of each room of the house. I turned the box fan OFF so we could see the natural convection currents.

Wow. Wow. Insane. We can *see* the air moving, and it *is* moving. A lot. NEWSFLASH: HEAT IS MOVING ITSELF THROUGH THE HOUSE ON ITS OWN. I am now more convinced than ever that the best thing we can do is hang onto the BTUs rather than trying to move them aggressively from room to room.

The air movement on its own, without the box fan assist, is pretty impressive. Gonna check it again with the box fan running, but given this visual, I'm going to leave the box fan off more than on, I think.

Beca, as always, your posts are thought provoking.. I was just mentioning to my wife, who's sitting next to me, that my feet were cold. Odd. I don't remember having cold feet before. Now before you get into a medical issue, I mean the kind of cold that feels like a cold draft. The room the stove is in is super insulated and most of the rest of my house is as well insulated as you can get with a 200 year old house. That said, there is always a draft of cold air coming from the back rooms but where I sit, I usually can't feel it. I was getting all excited to TP my house when I remembered that we had removed the fan we have sitting on the floor at the entrance to this room because of all our Thanksgiving company. Could that have made a difference? After all, I would be INCREASING the flow of cold air to the stove. Well, after putting the fan back on the floor and turning it on, no more draft. Weird how the airflow works. I'm happy and my dog's happy because he sits in front of the fan all year round. (I did see if there was a difference with him laying in front of the fan and not...no difference.) I think I'll still hang some TP around the house just to see.

 

[becasunshine]

Jimfrompa, the whole "open window acts as a chimney and draws heat to that end of the house" should work, technically, but as Briansol says, the heated air that goes out of the window will create negative pressure- the air that goes out of the window will have to be replaced somehow. It won't be replaced by your pellet stove- the combustion side of things should be a closed system if you have an Outside Air Kit, an OAK, installed on it. Stove draws in its combustion air through the OAK, uses it for combustion, expels the exhaust gases out of the combustion side vent into your chimney or out of your direct vent and out of the house. Wash, rinse, repeat.

If you don't have an OAK, then your stove is drawing combustion air in through every tiny gap and air leak in your house to take the place of the volume of air that the stove is sucking up as combustion air, then sending out of the exhaust vent pipe.

The convection, or room air, side of the stove draws air in from the room, sends it through the heat exchange system to get heated up, then pushes that volume of air, now heated, back into the room from whence it came. Convection currents send that warm air rotating around your room and your house but no volume of air needs to be replaced from this process.

Aside from that, if you open a window at the other end of the house, the heat will travel to that window and out of it, certainly, because as you say, heat flows to cold. The volume of air that flows out of the window will need to be replaced, so cold air from outside will come in through every crack and leak into your house to fill that volume.

If you don't have an OAK hooked up to your stove, then cold air is already coming into your house to replace the air your stove is taking out of the house for combustion. If you open a window in this situation, you are giving that replacement air a superhighway into your house.

If you do have an OAK, then the open window is letting heated air out, and cold air will come in through other gaps in the house to replace it.

I am no expert on wood stoves- my knowledge is second hand and quite dated. I remember old school wood stoves from the 70s and 80s. I don't remember any wood stoves that had their own OAK (although, apparently, many now do.) Of course that big ol' wood stove fire was drawing air from the room for combustion- and it was putting out big blasting radiant heat. What happened in that situation, and I can attest to this from other people's houses at the time- the area right around that big honkin' radiant chunk of metal wood stove was *very* warm. In the further reaches of the house, remote from the wood stove, cold air from outside was flowing into every gap in the house- so while the area right around the wood stove was hot as blazes, you could see your breath in the upstairs back bedroom.

My recollection was that people with wood stoves opened windows because the wood stove was cranking out too many BTU's for that day's weather. An open window in the house may have been a safer solution than trying to burn the old school wood stoves too low- creosote in the chimney from gases that cooled too quickly. In that case, open the window in the back bedroom upstairs, try to draw some of the excess heat in that direction.

But that is all ancient memories from a person who wasn't directly in charge of the wood stove at that time.

Pellet stove heat is much "gentler." It puts out BTU's but much less per hour, usually, than a wood stove. We have to hang on to 'em when we make 'em! That's why people recommend a fan pointed at the stove- to give a little boost to the natural convection currents- although as other posters have noted, other solutions may work better for them in their individual configurations.

 

[becasunshine]

"I was just mentioning to my wife, who's sitting next to me, that my feet were cold." ChandlerR, it's a little late in the game for cold feet. I'm just sayin'.

"I remembered that we had removed the fan we have sitting on the floor at the entrance to this room because of all our Thanksgiving company" It's amazing how putting the fan in even a slightly different place changes the currents all around.

"(I did see if there was a difference with him laying in front of the fan and not...no difference.)" I would do the *exact same thing.* I am not kidding. I would. HEY A 75 LBS. DOG HAS SOME DISPLACEMENT!

"I think I'll still hang some TP around the house just to see." The TP game is fun! It's really cool to see how much air is moving... it blew my mind. I had no idea that the natural convection currents were moving that much air around our house.

So all over the world tonight, Hearth.com members are roaming about their homes with rolls of toilet paper and rolls of tape, taping strips of toilet paper up in doorways to look at air flow... and geeking out over it... but some members will figure out how to optimize their convection currents and there will be goodness in this!

Rowerwet and P38X2, this circa 1958/1959 house had replacement windows when we purchased it in 2006. That much was done. I *clearly* remember the home inspector standing beside the house, noting that it is authentic brick and block construction and that it has no wall insulation but that it does have mass. I find myself wishing that I knew then what I know now. We may or may not have bought this house on that factor but knowing what that meant, really, would have helped us have a better idea of what we'd need to do and even what could be done in terms of utility cost savings. As it is, our utility bills are quite reasonable, so I shouldn't complain.

We are returning from our son and daughter in law's home, a house in a cooler part of the state, in the mountains. Their house is 1940's vintage, so it's at least 10 years older than our house, perhaps almost 20 years older than our house. Their HVAC thermostat is set higher than ours- baby in the house- but I was amazed at how much warmer their house felt- and not just by thermostat heat. Even though their walls are plaster, their walls aren't cold, and that makes a difference. They also, apparently, based on a cursory examination today, do not have big gaping air spaces around their electrical fixtures (outlets and switches) where they fit into the walls. The plaster edges around some of our electrical outlet boxes had chunks missing; we had to repair edges so that the insulating inserts would be effective. Even then some of the holes around the boxes were huge. We should probably get some spray foam insulation and put it around the boxes themselves- but I want to be very, very careful and get good information so we don't start a fire in our walls. =0 =0 <=3 =8X The exterior of their home is all brick as well, and their interior walls are plaster. I don't know what's going on inside their walls but their walls are not cold to the touch like ours. Maybe their house was amenable to blown in insulation and a former owner had it done? Maybe they keep their home warmer all the time, so the walls have absorbed that heat? I don't know.

Evidently our house was built during that sweet spot when energy to heat homes was cheaper than building materials...?

Our pellet stove puts out max 43k BTUs and we have to work hard to spread those BTUs out around the house before they dissipate. Or whatever BTUs do. Wherever BTUs go to die. In my house. BTUs go to my house to die.

Geez, that's just sad.

Now I want a big honkin' Harman.

 

[becasunshine]

P.S. Rowerwet and P38X2, yeah, we did have to put additional weather stripping on one of our replacement windows- a casement window in which the original stripping is integrated. The original stripping is still OK, and we couldn't detect a direct draft, but the area still felt cold. We added some weather stripping and we can feel a difference.

Otherwise, most of the windows in the house are outfitted with cell shades (we have vinyl blinds on the window over the sink in the kitchen and the window in the laundry room for ease of cleaning) and we have curtains over the cell shades in all but one room. In that room, the cell shades cover both the window and the frame (high slider with no sill.) The room doesn't get direct sunlight so other than a minimal additional R value, I don't know what curtains over those cell shades would do for us. Where the cell shades sit in deep window frames, and there's a tiny gap in between the cell shade and the window frame, we can feel a bit of conduction/convection cold from the glass through this tiny little gap on very cold nights. We put butt ugly thermal curtain panels over those windows and it does help.

It's funny, this conversation came up over Thanksgiving dinner. My father in law, an engineer by trade, was commenting that the R factor in all windows is contextual. The R value of replacement windows may be double the R value of original/old school windows, but for most windows, he say, you are talking about increasing a value of R3 to R6. It's still like having a huge hole in the side of your house. Made me glad that we invested in cell shades and butt ugly thermal curtain panels.

 

[Sniz]

^ windows generally are not rated by R value, at least not in the trade. and yup, the best window is nowhere as good as an insulated wall. Not even close.

I work for Andersen fyi

 

[becasunshine]

^ windows generally are not rated by R value, at least not in the trade. and yup, the best window is nowhere as good as an insulated wall. Not even close.

I work for Andersen fyi

I am woefully ignorant about this. =( How are windows rated? Most of the windows in this house are Regal replacements, I believe they are standard issue, not their top of the line. I could be wrong about this but my impression is that the available upgrades are mostly about latches, etc. rather than insulation value. A few of our windows are sliders and casements and those are another brand... Skyline? I think? They do not appear to leak.

It was cold around the casement, so we added some weather stripping- it seems to help.

At any rate, we have swaddled up the windows. I don't think the windows are our primary problem right now. I think our problem is no wall insulation and perhaps a slightly undersized stove.

 

[Madcodger]

Windows are primarily rated via 1) U-factor, which is the inverse of an R factor and 2) Solar Heat Gain Coefficient (SHGC, or the amount of heat they allow in as infrared).

The other thing most people ignore is the installation of windows and doors using modern materials and techniques. You wouldn't believe the number of contractors who use neither. The window looks good, but leaks excessive amounts of air due to poor technique for installation (seen around the trim, not the window itself, although many people blame the window). In fact, new windows should normally be near the bottom of one's list of improvements from a cost perspective. Caulk (for existing windows) should be near the top.

To learn more about windows, here is a link to an excellent article from Fine Homebuilding magazine:
http://www.finehomebuilding.com/how-to/articles/understanding-energy-efficient-windows.aspx

 

[SmokeyTheBear]

Beca your FIL is correct about the effect of a new versus old window and if you look around a (double pane) window is basically an air gap and surface air films the insulation value is pitiful compared to wall even a standard plastered inside brick wall outside. However taking the R value from 3 to 6 is a huge heat loss reduction when lots of window area is involved or the difference between inside and outside temperatures is large. Total heat loss is proportional to the (temperature difference divided by the r-value) multiplied by the area of the surface. Doubling the surface area doubles the heat loss, doubling the temperature difference doubles the heat loss, doubling the r-value halves the heat loss.

Any air infiltration is even more problematic.

There is a special heat loss calculator provided by hearth.com member GaryGary that allows one to calculate the energy reduction possible (he has a number of them on his site www.builditsolar.com).

He has a section that is called the half program where he lays out projects that can under the correct conditions cut one's energy consumption in half.

There are a ton of ideas on that site or pointed to by that site, it is well worth the time spent there reading.

 

[becasunshine]

Beca your FIL is correct about the effect of a new versus old window and if you look around a (double pane) window is basically an air gap and surface air films the insulation value is pitiful compared to wall even a standard plastered inside brick wall outside. However taking the R value from 3 to 6 is a huge heat loss reduction when lots of window area is involved or the difference between inside and outside temperatures is large. Total heat loss is proportional to the (temperature difference divided by the r-value) multiplied by the area of the surface. Doubling the surface area doubles the heat loss, doubling the temperature difference doubles the heat loss, doubling the r-value halves the heat loss.

Any air infiltration is even more problematic.

There is a special heat loss calculator provided by hearth.com member GaryGary that allows one to calculate the energy reduction possible (he has a number of them on his site www.builditsolar.com).

He has a section that is called the half program where he lays out projects that can under the correct conditions cut one's energy consumption in half.

There are a ton of ideas on that site or pointed to by that site, it is well worth the time spent there reading.

Smokey, I'm going to check that site out thoroughly.

I've typed out our house configuration a million times on this web site- sorry Regulars, Admins and Mods! My house is probably engraved on your retinas by now! but we are *still* working on efficiency here.

The windows are the windows. It's not worth it to us at this stage in the process to rip them out and replace them with different windows with a bit more efficiency. We've put cell shades on them, curtains in some rooms where the cell shades cover the entire window and the frame, butt ugly thermal curtain panels on windows where the shades sit in the frames and there's a tiny gap on either side of the cell shade.

This evening we are going to begin caulking up some gaps around the perimeter of the floor. The hardwoods have been sanded to be refinished a couple of times, and the house has settled, causing a gap in between the quarter round, the baseboards, and the floors in some places. I swore I was feeling a draft coming in through those gaps. At first I thought I was being ridiculous- really? But then it got cold early this year, and we've sealed up a bunch of other things- making those drafts sort of stand out on their own.

I was not being ridiculous- it's quite real. I looked it up online and I'm not the only person on Google complaining about this problem. The recommendation? Caulk. I believe Madcodger and I discussed caulking around the floor perimeter on another thread- or was it this one? Anyway, IT BEGINS TODAY, MADCODGER- THE EXPERIMENT IN CAULKING BASEBOARDS.

My husband hates caulking- but he's doing this to make me happy.

In other news- the tops of the walls appear to have sill plate or something finishing them off where they meet the attic, so at least the walls aren't acting like little chimneys.

OK, now I have to go wipe down some baseboards so my husband can caulk. It's the least I can do.

 

[EZsteve]

Ok so I will pipe in with my two cents about moving heat around my house. So every year I forget what works best and mess with it until I get it right.I have 12ft ceilings I'm my bed room and if I do nothing it will 74 in my living room and 61 in the bedroom. My house is wide open rancher for the most part. My bedroom is right off the living room and can be 12 degrees different easily. Every year I try moving the heat with ceiling fans and it never works. Even though I hate the noise and the cold air blowing in to the living room it is the only way to heat up my bedroom. Small 8in fan at bottom of the door blowing into the living room from bedroom can get the bedroom with in two degree of the rest of house. Works like a champ.