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"Moving Heat" : Convection Air Currents in Your House

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by becasunshine, Nov 28, 2013.

  1. becasunshine

    becasunshine Feeling the Heat

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    Steve, do you have a ceiling fan in that lofted bedroom? That may help as well...

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  2. EZsteve

    EZsteve Member

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    Yes..but for some reason it does nothing. That is why I try every year an fail. I would love to use the ceiling fans in the bedroom and living room. I have tried every configuration ...one blowing up and one blowing down and vise versa... both up and both down..but in the end they both have to be off , with just the small fan at doorway. Its the only thing that works.
  3. becasunshine

    becasunshine Feeling the Heat

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    We have to use a box fan sitting in the floor of the room with the stove, pointed into the room/at the stove. That's what works for us in terms of facilitating the natural convection. Cold air at the floor is pushed into the room with the stove; warm air at the top of that room is pushed out. The volume of cold air displaced by the fan pushing cold air into the room with the stove encourages the heated air above to move in the circle to fill that void. So, I agree- a ceiling fan would not facilitate that movement.

    I was wondering if the ceiling fan could perhaps push the heat that's gathering at the top of that 12' ceiling back down into the room. ??? We have 8' ceilings in this house so we don't have to do that here. I completely agree with you- in terms of moving the heat room to room, ceiling fans have not worked for us.
  4. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    It can push it down to some degree and in doing so it can interfere with other air movement in the room. Sort of like people punching multiple holes in a stove room ceiling but not providing something a bit further away for the cold air to fall down thus completing the convection loop. Having the fans attempt to send the hotter air against the ceiling works to a small degree (depends upon how well the ceiling is insulated) since the natural movement would be up provided there is a corresponding natural down. Large ceiling fans can work against each other especially if you can't run them a very low speeds.
  5. shore72

    shore72 New Member

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    Hello, folks-complete newbie here, and this looks like a very helpful thread (and forum in general.) We just received a used Englander 25-PDVC from a friend, and are trying to decide which room to install it in. My wife is concerned that if we put it in the living room it will run us out of there. The next best option is a rarely used dining room. Closest to the center of the house would seem like a good idea but that would require a pretty long vertical stack, which I've been told isn't a good idea. Anyway, any comments regarding this little stove overheating us (or not) are welcome.
  6. becasunshine

    becasunshine Feeling the Heat

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    As far as putting that Englander in your living room with you, my personal opinion is that it won't run you out of the room. Pellet stoves aren't like wood stoves in that regard. The heat is a lot more gentle. If anything at all bothers you in the living room, it will be the blower/convection fan noise. Unless the fan is really noisy, you'll probably get used to that too. We keep our Napoleon's convection fan set at about midway on the dial. I don't think it's too loud.

    Lots of people on the forum have their pellet stoves in their living rooms or dens with them.

    Your Englander 25-PDVC is rated to heat up to 1500 sq. ft. Our Napoleon is rated to heat up to 2000 sq. ft. Our house is 1410 sq. ft. We are just getting to the point where, with enough attic insulation and caulk and spray foam insulation and cell shades and thermal curtains on the windows, that the Napoleon will carry our entire house comfortably by itself. It's not the Napoleon's fault. We are finally getting our heads wrapped around just how drafty this 54 year old house really was.

    We would have put our Napoleon in the living room with us but the layout of the room (windows, exterior door, interior doorways, etc.) just wasn't conducive to it. Our Napoleon sits in a bedroom on one corner of the house that we converted into a den. We typically sit in the living room, just across the hallway from the room in which the stove resides.

    If anything, we were a little too cool in the living room on the coldest of nights. We have been working on this in increments and I think we are *finally* getting on top of it.

    We are supposed to have a real winter this year- I think you'll be warm and cozy with your new to you Englander. Congratulations! Englander's customer service is legendary. One of their service engineers, Mike Holton, is a regular on this board. His forum handle is stoveguyesw. He's a great asset to this community- he's an invaluable source of knowledge and experience and he's always willing to help.

    Enjoy your new stove!
    newbieinCT likes this.
  7. Madcodger

    Madcodger Guest

    Where you place it depends to a large degree on room size, layout of rooms, etc. If you can post a room layout with rough sizes we might be able to provide more info. We have ours in a LR that's about 26x15 with a half cathedral ceiling. Doorway into it is 6' wide. Heats much of that entire floor, and room is incredibly comfortable, about 2 degrees warmer than rest of that floor. Perfect for sitting and watching TV or reading.
  8. shore72

    shore72 New Member

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    Thanks for the quick help-I'll have to work on drawing a little diagram. My wife & I both grew up in houses with woodstoves and can well recall how uneven the heat can be. Our house was built in 1950; both of the rooms this stove will work in are chopped up with lots of windows and doorways. 2 of my 3 choices would actually be in front of a window, venting straight out underneath the sill. Our house is about 2000 sq ft total, but we are only trying to heat about 1/2 of that. I've actually never seen/heard any pellet stove run!
  9. becasunshine

    becasunshine Feeling the Heat

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    Hey, check the local codes on venting below a window. There are specific clearances from the vent to any opening into the house: windows, crawl space vents, vents of any type, mechanical vents, etc. There are also clearances to flammables, to the ground, to public walkways, and to gas and propane sources. The stove's owners manual has a lot of information about stove placement, but there are local codes as well.

    It would be a real bummer to cut a hole through your house in a spot that's not recommended due to safety reasons, or that is not up to code.

    You can probably find an owner's manual for your stove online- that's a good place to start. Your county or city gov't offices maybe could help as well.

    P.S. You know that you can plug that baby in and turn on the blower before you install it *anywhere* to get an idea of how loud the fan will be, sitting in the room with you.
  10. shore72

    shore72 New Member

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    I'm glad you mentioned about the window issue-dumb thing is, I did find the manual online last night (England has a great website) and saw what it said about clearances. For some reason it didn't click in my head about that issue in my case. That really narrows it down for me.
  11. becasunshine

    becasunshine Feeling the Heat

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    You might want to start a thread to ask about possibilities. We went with a direct vent; we have as good of a situation as it gets for a direct vent, and we were in a position to give up a bedroom/change that room into a den to accommodate a stove. If a direct vent limits your choices too much, you may be able to use a traditional vertical rise with a chimney- not a masonry chimney, but a chimney made out of whatever clad level pipe is appropriate.

    These 1950s houses are great in some respects: they aren't ridiculously super-sized and it is possible to heat them with a stove. Our construction is awesome. We had two layers of shingles peeled off of this house to replace the roof when we bought it and the roofers didn't find a single rotted board. We've had to replace a few subfloor boards in our renovations, but in both places, the bathroom and the threshold by the back door, the damage was caused by water leaking into places where it shouldn't have been. We've not found a single board that has failed due to normal wear, after over 50 years.

    On the other hand... insulation wasn't as big of a deal back then, so there's not an abundance unless you add it, and the rooms do tend to be smaller, and the floor plans a bit chopped up.

    Never say never, however, it can be done! :)
  12. Countryboymo

    Countryboymo Feeling the Heat

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    Talking about retaining BTU's and heat loss made me remember my energy audit a few years back. I had horrible duct leakage and poor duct design and quite a few air leaks. The most memorable is when he put a cfm hood on the recessed lights and checked the air leakage. It was an average of 4 cfm per light with 14 lights which doesn't seem alarming until you start calculating.

    56cfm total almost one cubic foot per second.

    3360 cubic feet per hour

    80,640 cubic feet per day.

    The wind speed was 5-10 mph which is below average wind speed here at time of testing.

    I have no codes so I went to walmart and purchased 1.50 styrofoam coolers and a knife and covered and caulked the lights with styrofoam safe caulk since the bulbs are all cfl or LEDs and the heat is not a factor. I also purchased air sealing trim rings off ebay since they were much cheaper than home depot or lowes. I left bricks on the coolers that did not need caulk and just put some weatherstripping on the bottom.

    I had someone argue that some air was probably coming in and other air going out so it might be 40k per day. Who cares? Air is leaving that shouldn't be and its an easy fix and even if it is 40 it is still alarming.

    After fixing duct issues, sealing ductwork and a few other air leaks I dropped the air leakage so much I am able to heat the house with 10kw of heat strips instead of 20 and satisfy the stat. I replaced the 3.5 ton heat pump with a 3 ton but did upgrade from a 13 seer to a 15 with demand defrost and much better numbers.

    House was built in 2006 and is 1800 sqft with a partially insulated basement. I can't imagine the impact of sealing and adding insulation to a older home.

    I already had added attic insulation before the audit and just have the basement to finish insulating. I am still in the sealing mode.

    In the heating months I leave the air handler in circulation mode and it runs at 200 cfm to help keep the air moving from room to room and circulate the warm air coming up from the castile in the basement. When it gets below freezing I run the castile on medium and when it gets much below 20 I run it on high. The thermostat has an outdoor temp sensor and shuts the heat pump off below 10 degrees and runs solely on strips and the pellet eater which is usually on when it is that cold.

    Every dollar and hour that is spent sealing will pay off twice as fast as time insulating. Insulating is a huge factor but I don't care if you put R50 in the attic if you are passing air through it the R value goes to the toilet.

    Sealing the recessed lights cut the dust in the house in half because that air moving was sucking dust and fibers out of the insulation and attic.

    Thermal imaging cameras are a must.. they do not lie and show leaks and poorly insulated areas like night and day.

    Sorry for the rant. To see the actual numbers and images of the air moving it just shows dollar signs heading out into the atmosphere.
  13. becasunshine

    becasunshine Feeling the Heat

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    Dude, rant away. In fact, I'll see your rant and add another.

    This is the first house we've owned in which combustion appliances are housed within the conditioned living space. The gas furnace and the gas water heater are both in the laundry room, side by side. They vent into a shared chimney.

    During the home inspection, my father-in-law, an engineer, and the home inspector stared at the water heater vent for a good long time. It has a horizontal traverse to the place in which it exits the wall to vent into the chimney. It does have a vertical rise along the the length of this traverse, but it also has a bend in the pipe to accommodate the horizontal movement, and the bend is relatively close to the hood over the actual water heater. Yadda yadda.

    They did some calculations and decided that the vertical rise vs. the horizontal traverse met code, but there was talk of drafting and back drafting. The two guys decided that the homeowner had left the window in the laundry room opened so that the water heater would draft efficiently. They recommended leaving that window cracked all the time, so that the water heater would draft, efficiently. I noted that the laundry room bone was connected to the rest of the house bone and that the entire skeleton would freeze, or get very hot and humid depending on the season, and that the entire skeleton would likely object to the impact of a continuously opened window on the utility bills.

    They then recommended that we keep the window in the laundry room opened all the time and the door to the laundry room closed all the time.

    *Insert Lay Person Secret Eye Roll at Engineering-Types HERE.*

    I looked around at the situation, at the room, at the house, at the water heater, at the vent pipes, and I seriously doubted that the home owner left the window in the laundry room opened so that the water heater would draft efficiently. I decided that the homeowner had left the window open in the laundry room because she had a cat and the cat's litter box was in that room. She left the window opened just in case Kitty dropped the Poo Bomb after she left the house.

    So when we moved into the house, I parked a CO alarm in the outlet right next to, as in almost touching, the water heater and went on about my life. The idea that the water heater's vent may not be drafting as efficiently as it should never completely left my mind, but we kept the dual powered (a/c and battery back up) CO monitor right there, and we changed the batteries twice a year, faithfully, and life went on.

    The CO monitor never uttered a peep.

    Of course, the house was so, ahem, "breezy" that we were self-ventilating.

    Now that we are seriously, seriously sealing up this house, the idea of the water heater vent loomed larger in my mind. First of all, we calculated the age of the two CO detectors that we have here- one in the laundry room with the furnace and the water heater, one in the stove room. Both were over 5 years old, so we replaced them.

    Then we revisited that water heater vent. I did a "stress test" with exhaust fans running, the dryer running, the furnace running, and the water heater fired up, and it appeared to back draft- it fogged a mirror that I set next to the hood.

    I called our HVAC company immediately. They also deal with gas water heaters and they came right out.

    Turns out that I didn't let the water heater run long enough before I popped the mirror up next to the hood. Once the vent pipe heated up, the water heater drafted just fine- so well, in fact, that the HVAC company's much more sensitive CO monitors (they tested with two different types) picked up zero to negligible parts per million CO at the vent hood. We did the mirror test again, and with the water heater (and everything else, exhaust fans, furnace, dryer) running full tilt, and the mirror did not fog.

    Here's what we didn't see coming:

    The *other* end of the water heater's vent pipe had become, at some point in the past, unsealed from the wall.

    The terminus of the vent is tucked up in a corner on the other side of the air handler, which is on top of the furnace. To say that I don't routinely pay a lot of attention to that remote corner of the house is an understatement. I don't do a lot of deep cleaning behind the furnace. I vacuum all around it, I mop the floors, etc.- there's no debris built up back there- but I don't routinely "dust the furnace" or the vent pipes where they duck behind the air handler.

    Our HVAC tech was inspecting the vent pipes and all of the sudden he said, "WHOA! LOOK AT THOSE COBWEBS!"

    I'm a little particular about my house keeping, dark undersides of the furnace and air handlers not necessarily included in that compulsion, so I took exception. "WHAT COBWEBS? YOU FOUND COBWEBS? STOP STARING AT MY COBWEBS! IT'S NOT POLITE!"

    HVAC Tech said, "No, not worried about the cobwebs- look at the air movement! Your gas water heater vent has come unsealed at that end!"

    So while I'm all worried about the hood end, the other end has pulled itself out of and away from the wall- enough that the combustion gases rising up the vent were causing those rogue cobwebs to flap in the breeze.

    The HVAC Tech had used all the sealant in his truck but he post haste went to the plumbing supply store, bought more sealant, came right back to the house and sealed that vent.

    I have no idea how much CO was spilling from that end of the vent but it couldn't have been too bad- the CO alarm never went off, and never registered any number other than zero at any time that I looked at it.

    I do wonder how much of our heated and cooled conditioned air went up our chimney through the rather large gap left by the duct coming unsealed from that opening in the wall. Even though that hole is tucked back behind the air handler there is some room for air flow back there- and it is located, unobstructed, in the conditioned envelope of the house. It would be the equivalent of having a pretty big hole in your exterior wall- or, as my father-in-law and the home inspector said, "Leaving a window opened."

    While I feel a little foolish for calling our HVAC guy, God love him, to our house to measure zero to negligible CO levels, that was a good catch, and we will probably make the cost for that service call up in short order by not sending heat up the chimney through a hole in the wall.
  14. Charles1981

    Charles1981 Minister of Fire

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    I have about 1800-1900 sq feet to heat. First floor is fairly open plan, bottom floor walkout is a little more boxed in. My stove is in the basement however there is a spiral stair case next to the stove with ceiling fan directly above it. I also have two floor registers over the stove between the walkout and first floor.

    With the ceiling fan blowing cold air down to the basement there is a huge column of warm air shooting up through the registers. It is about 87 in the stove room. Without power and no fans heat doesn't go upstairs (can get it up to 66-67 upstairs while it remains 87 in stove room). Turn the ceiling fan on and the upstairs will heat to 74-75. The bedrooms do need a fan blowing towards the main room/spiral staircase to warm up appropriately.

    The bedroom in the walkout next to the stove will be 68 degrees while the stove room adjacent is 87. Turn on the fan and the bedroom quickly warms up to 76-77. Upstairs bedrooms don't get as warm and are downright cold without the fans blowing towards the main room. But with the fans can get to 69-70ish. Not bad.

    The upstairs bedrooms are guest rooms and if we have guests over we turn on the electric baseboard heat at night to make sure they stay comfortable as they typically keep the doors closed to sleep.

    Without the fans and air circulation however the house other than the stove room does not stay very comfortable.

    Attached Files:

  15. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    From a heating the air stand point that per minute figure is what you pump out a lot of which you have heated and then there is the same amount that you attempt to heat because what goes out must come in via other leaks. Most pellet devices can barely move that amount of air per minute. Some can but a lot of units can only come close running wide open. It is not just recessed lights that are a problem normal ceiling fixtures can have the same issues if not properly handled.
    Countryboymo likes this.
  16. Harvey Schneider

    Harvey Schneider Minister of Fire

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    Where did you get this notion that heat flows to cold. In air movement, warmer air rises because it is lighter and cooler air sinks because it is heavier. The convections caused by this may stir the air. The warm air has no idea where the cold air or window are and has no mind to go there.

    What will happen.
    Most houses run at a slight negative pressure due to warm air rising through leaks around ceiling fixtures, exhaust fans and other perforations in the ceiling. As a result of that slight negative pressure, cold air will be drawn into the house.
    The exception to that is if there is a prevailing wind that puts the open window on the downwind side of the house. That prevailing wind causes a low pressure that may suck air out of an open window. If that happens the pressure in the house is lowered even more and cold air will leak in somewhere else to equalize the pressure.
    If you open a window in the winter, one way or another, cold air will come in.
    Last edited: Dec 5, 2013
  17. becasunshine

    becasunshine Feeling the Heat

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    The Second Law of Thermodynamics?

    But I agree with your description of the convection cycle, and I can see how your description of houses having an inherent negative pressure can work as well.

    In fact, it occurs to me that your description of "negative pressure" is exactly what was/is happening with this leaky old house! (although we've sealed up every ceiling penetration that we can find and/or reach.)
  18. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    By conduction it does and conduction is very low in most gasses.
  19. becasunshine

    becasunshine Feeling the Heat

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    Smokey, I'm being a little dense here.

    Harvey Schneider's challenge made me think. I've always gone with "heat flows to cold" as an explanation for a lot of things, so when he challenged the idea of an open window as a chimney and proposed another explanation, I plugged that explanation into my scenario to see how it worked.

    I could see it, because we are sealing up the house to keep cold drafts from coming in. In particular, we caulked around the perimeter of the hardwoods because I could, on the coldest days, literally feel cold air coming through those cracks. So, if one believes in The Second Law of Thermodynamics, there has to be an explanation, because cold doesn't move to hot unless there is additional energy put into the system, or unless it is being "drawn in" by a chimney effect.

    There are so many "moving parts" in a house system, even if to one's naive eye, the house appears to be sitting completely stationary. ;)

    My husband has gone up in the attic and visually inspected each and every penetration through the ceiling that can be reached without pulling up the board flooring. There is a strip of board flooring from side to side in the attic, and it is blocking access to one (1) ceiling fixture. If all of the other ceiling fixtures in the house are an appropriate guide, that one ceiling fixture should not be a problem. It should be pretty tight.

    I don't know what could be acting as a chimney in this house, although I suppose it's possible that tiny cracks and gaps that aren't readily visible to naked eye inspection (no thermal imaging) add up to a significant chimney. What I do know is that cold did indeed flow to heat in this house because we could feel cold drafts coming into places where there were visible gaps.

    I should amend that statement above, about what could be acting as a chimney- since our HVAC Tech found the gas water heater vent unsealed from the wall, and my cobwebs flapping in the breeze, the chimney itself may have been acting as a chimney. Imagine that!

    I'm not being snarky here, not at all- please draw it out to me, the relationship between conduction and gases and The Laws of Thermodynamics- because I am literally trying to apply that stuff to solving the problem here without causing new ones (i.e. sealing up the house incorrectly, such that we end up with other problems and perhaps don't even address the original problems effectively.)

    Also, this question is nagging at my brain- we went through and put insulated inserts behind all face plates to all electrical outlets and switches, both on interior and perimeter walls. We didn't do the spray foam thingy around the outside of the electrical boxes where they sit in the wall- we just did the face plate insert thingy. This is going to drive my husband bat poop crazy, but is there an advantage to doing both? In one switch on an interior wall, I had to piece together some additional insert material because the gap around the box and the hole in the wall were so big. On other holes for outlets, I did a little repair to the plaster and let it dry before putting the face plate and insert in place, because the hole was so big.

    Foam plus insert seems redundant. The Hubs hates working with that spray foam in really tight, picky, possibly visible places because it can be a mess, so I thought that the inserts made sense and less mess overall. Now I'm reading that people do both...??? and also that some people caulk the insulated inserts in place...???

    The only thing that could make Mr. Sunshine any happier about re-addressing all of those outlets and switches with spray foam is the possibility of addressing all of them with spray foam *and* caulk.

    I think his head might explode.

    Is it worth it?
  20. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Let's see exploding heads vs what might be a reasonable thing to do.

    You want the air leak stopped, so whatever does it is the right thing to do, after that you can debate about the possible conduction losses.

    If you get him really agitated please have a camera rolling we just love pictures on this forum ;) .
    becasunshine likes this.
  21. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Heat (energy) is transfered by radiation (think sunshine across a vacuum) equally in all directions away from the energy body, conduction molecule to molecule always from hot to cold, and convection (gases and liquids) prevalently by displacement normally due to pressure differences.

    Personally I'm from the old school heat is a liquid that I brew in my fermenters for the long cold dark days of winter, that's my story, and I'm sticking to it.

    Currently making a spiced mead.
    becasunshine likes this.
  22. becasunshine

    becasunshine Feeling the Heat

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    The Hubs made a Baltic Porter as the Christmas Beer this year. A few have "come out of the bottle" already. He says it's good. :)
  23. Harvey Schneider

    Harvey Schneider Minister of Fire

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    At the temperatures we are dealing with radiant transfer is almost non-existent. Things need to literally glow to radiate heat in any significant amounts.
    Conduction in air is almost non-existent. The molecules just aren't connected to each other tightly enough for the energy to pass from molecule to molecule (yes I know about molecule collisions tranferring energy)
    The primary means of heat transfer in room temperature air is convection.
  24. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Hey, I didn't say one thing about in this particular situation I just laid out the three ways energy gets transfered.

    All bodies above absolute zero radiate, no "glowing" needed, and what constitutes a significant amount varies :p .
  25. Madcodger

    Madcodger Guest

    Not to step on Smokey's answer or anyone else's when they make it, but if you really want to dive into this area, Beca, here's a link to get you started: http://www.sensiblehouse.org/nrg_heatloss.htm

    The US. Dept. of Energy also has some good info, and my two favorite journals that deal with these issues often (for contractors and architects) are Fine Homebuilding and the Journal of Light Construction ("Light" meaning pretty much any residence, as opposed to a skyscraper or highway). The bottom line is that the two things homeowners need to worry most about are 1) air infiltration and leakage and 2) losses through the construction materials themselves, but not via air to air exchanges of heat.

    Air leakage / exchange (convective loss) is important because heated air that leaks out MUST be replaced, and it can only be replaced by air from outside, that is both colder and drier (or the opposite, in the summer). The "tighter" you can make your house, they less they will occur. If you get the house too tight (lower than 35% of the home's air being exchanged each hour for a typical family) then you need to figure out a way to bring in more fresh air and lose stale air, generally through a heat or energy recovery ventilator. That's not normally the problem for older homes, though... Once you stop that air flow, you have done all you can do to stop convective losses. You can't make something "more stopped", in other words, so if you have stopped the flow of air through a hole (whether that hole is something cut in the side of the house or an electrical outlet with a path to the attic through the wall stud bay), you've got that specific thing covered. "Stopped is stopped", for CONVECTIVE losses. But that's not true for CONDUCTIVE losses.

    Conductive losses are the reason most common insulation materials are used (like blown cellulose or fiberglass, or batts) in areas like the walls and attic of a building. These generally do very little to stop convective losses, because air just goes through them (although it may be inhibited a bit, it's not all that significant). But they do a nice job of stopping the heat loss that occurs by the transfer of energy (heat) from one building material to another or ultimately to the outer layer of a building, where the energy (heat) is transferred to the air (which is really just the "stuff" that the outer layer is connected to). This is what someone is referring to when the discuss the 2nd Law of Thermodynamics. If you want to boil that down in layman's terms, it just means that things will seek an equilibrium, or common point. Because heat is really just energy, the thing with more energy (the hot thing) will lose energy to the thing with less energy (the cooler thing) until the two reach a common point (i.e, they are the same temperature). Apologies to my physicist friends for that oversimplification, but I think it illustrates the point for this discussion... That's why we say that heat moves to cold. It does, even in the absence of air movement. Insulation is designed to cut down on that conductive heat loss, and that's why we use it in buildings. And adding more of that WILL decrease the movement of energy (heat) because it creates a barrier between materials (or between materials and the outside air) that offers resistance to the flow of that energy (heat). It can't entirely stop it, but the more insulation you have, the more you will inhibit conductive (things touching each other, including air to a building) losses.

    So what do I ask myself when I'm trying to save energy? What TYPE of heat loss am I primarily trying to stop with the action I'm taking? If convective loss (air leakage) I do just enough to reliably stop the air flow. Anything more is not helpful. If conductive heat loss (stuff touching other stuff, including the outside world) then the more insulation I add, the better. And I do that until adding more is not practical because it is either not physically possible, or because the financial value of doing so is greater than the savings I will reasonably gain. Someone will now likely chime in about things like spray foam... That's a great insulator, because it can stop the flow of air AND inhibit conductive losses (in closed cell formulations). But given its expense, some builders will use it as an initial layer to stop air flow and get about 6-7 R value per inch of conductive insulation, and then add fiberglass or cellulose to get the remaining needed conductive insulation (R-value). They CAN'T get more convective benefit from additional foam, because "stopped is stopped" for convection. But conduction doesn't really have a "stop". You just add it as long as it makes sense to do so, in the least expensive (and hopefully environmentally responsible) way you can.

    Hope that helps...

    Joe (Madcodger)

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