Is there a (cheap) heat exchanger commercially available designed for a single room? If not, is there something functionally similar available? Finally, if this whole idea isn’t practical (or is simply too expensive), can anyone suggest another solution?
Here’s my situation: my “home office” is at one end of a (rented) single story house that has a sliding glass door to the backyard. There is a single doorway on the opposite side of the room to the rest of the house, with no additional windows or other vents. I smoke, my wife does not; the door to the rest of the house is generally kept shut (for obvious reasons). Most of the year, this is fine – I keep the sliding glass door open. However, with winter coming on, I’d like to set up ventilation that maintains some semblance of heat retention. Because it’s a rental, I can’t make any structural modifications to the house (such as putting a hole in the wall for a vent).
I think something like this would work, with a little DIY insulated panel that fits in the sliding glass doorway. Naturally, I don’t want to spend $500 on it (actually, I don’t have $500 right now). Besides which, the linked to item is not only much larger than I need (pumps 3-4x more volume), but I also have no need nor desire to integrate it into the main heating system.
If there’s no such beast, I’m all for rigging something up myself (as I was going to do anyway) – as I mentioned above, suggestions or ideas on alternatives are welcome (with the exception of quitting smoking, thank you). Also, I’ve tried HEPA filters and the like and they’re just not adequate.
I think that HX you linked to is pretty much the right idea, but expensive. You might be able to rig up some sort of exhaust system with a very small utility fan* , some flexible duct (perhaps the vinyl type sold for dryers, and some sort of box over the area where you smoke. It would basically be sort of a fume hood (think kitchen hoods) you sit under while smoking. You might even be able to find an old kitchen hood that you could convert to what you need, just remove the grease screen. Unfortunately, it probably won’t be pretty.
I’m afraid I can’t offer a better solution, but simply venting air to the outside as suggested by Dag Otto will blow that expensive heated air right outside (while causing nice cold air to be sucked in elsewhere). If I knew how the heat exchanger in the OP worked I could explain how to build one.
Where are you planning on bringing in the conditioned make-up air? Are you going to steal it from the rest of the house? A small exhaust fan + a transfer grille between your room and the rest of the house could work, but otherwise, you’ll be bringing in the cold air from outside to replace the exhausted air. This, of course, is a consideration when the furnace fan is not running…I’d imagine the supply air to the room is enough to keep the place positively pressurized during exhaust…but most people don’t keep their residential furnace fans running all the time.
Another problem is, without having a structurally installed vent, you’re going to have massive heat loss through the door, as you already know. I doubt you’re going to be able to easily put up a temporary R-19 insulated panel to exhaust through.
I think the simplest solution is a small exhaust like was mentioned above with a space heater near the doorway to combat the heat loss at that point.
Pretty isn’t a worry; a sort of fume hood is what my wife is suggesting and may very well form a part of the end result. My big concern (after the actual ventilation issue, of course) is the heat loss from piping air directly outside. I was contemplating how to do this myself – using the vented air to warm the incoming air by rigging up a duct within a duct type of deal. Naturally, a commercial exchanger would most likely be much more efficient, smaller, and all around better than anything I could construct. It’s not clear to me whether it would be more expensive – I haven’t yet priced the pieces/parts for my ad hoc solution.
Thanks for the link to the utility fan – there’s another wrinkle to this concerning the house’s heat which affects how I finally handle this. More about that in a subsequent post; but I wanted to note that I may have another (though related) use for just such a fan.
Exactly. So, from what I gather through studying diagrams and the like, I find it’s most easily thought of as an inverse heat sink*. That is, the cold air (from outside) is moved/forced through something that increases the surface area and is surrounded by the warm air from inside. Some of the heat of the exhausted air will be recovered simply through radiance. I haven’t been able to locate any detailed information on how commercial items pack this capability into such small packages, which I’m really curious about.
*Not quite, as a heat sink is a solid-air heat exchange that is only concerned with dissipation; also, there are no worries about filtering and/or keeping the substances unmixed.
OK, so this is where I explain the “wrinkle” I mentioned in my response to Dag Otto. We’re in a rural part of the PNW and we’re going to attempt to use the wood burning stove to heat the entire house. We have access to loads of free wood, and I’ve spent a good amount of time over the last few weeks designing and building an 8x8x10 “shed”, then filling it – chain saw, splitting wedges, etc.
The house is terribly designed – built in the '50s with little thought (it seems) for passive heating/cooling, much less airflow. So of course, the wood stove is located clear on the other side of the house – a single, relatively long, open area separates them. We currently have a fan set up that blows the hot air into the open space; it does a pretty good job, keeping the farthest rooms within about 5-10 degrees of the room with the stove. (As an aside, I’m really excited about buying some Seebeck effect circuits and putting together fans powered by the heat of the stove; but that’s deserving of a whole 'nother thread.)
Right. Although we hope to not use the “furnace” at all (scare quotes explained below). Which brings up another potentially useful aspect to this. The heating ductwork is run under the floor (forced air?) throughout the house. One idea that occurred to me was to put a utility fan (like one mentioned by Dag Otto) on top of the floor vent in the room with the wood stove, forcing the air from that room through the rest of the house. However, I don’t know how the heating system is set up; it’s electric heat, but I haven’t been able to find the main blower or anything that I’d consider a furnace. (You’d think it would be obvious; there’s only one place left that I think it might be – a “trapdoor” that my wife has covered. There’s no basement; the house is raised at most a foot or two off the ground/slab.) Since the blower/furnace is located between my room and the stove, is it even possible to blow air through the existing ductwork from one end of the house to the other?
Yeah. Although I’m hoping that something adequate is at least possible, and am given hope by a removable doggie door (something like this) that we used back in Indiana and wasn’t too bad. I was thinking of simply putting some insulation between two pieces of plywood, then doing whatever I had to do to seal it off. If I can’t find an adequate heat exchanger, I was thinking of running the intake and exhaust “ductwork” in the constructed panel as my own attempt at something functionally similar.
Which is what I might effectively do, although I’d like to have something better. As it is, I have some time and am willing to put in the effort – my biggest constraint is money. Plus, I’m rather enjoying tackling the problem and, as an added bonus, am learning quite a bit along the way.
Well, if the furnace blower isn’t operating, you’ll be able to get some air forced through ductwork from your position, but it won’t be a lot. The duct to your room is probably 8"-10" duct, and with any normal fan that’s cheap, you’re only going to be able to get about 200-400 CFM tops through there before the static pressure gets too high for the fan. Now, 400 CFM should be plenty provided the room isn’t too big, but if you’re just pulling (let’s be generous with the wood stove room) 78 degree air from the rest of the house, 400 CFM isn’t going to heat up the room that much if your exhuast solution is leaky, or poorly insulated. Of course, if you got a high-static fan, you could pull a lot of air through there…it’ll just be very loud, very inefficient, and you will still need to make up the air from somewhere if you’re exhausting that air out where you smoke instead of returning it to the house. That somewhere is outside…so you’ll start pulling a lot of cold air in.
Plus, the air won’t be that hot if you’re forcing from the floor mounted vent…the hot air in the room will be at the top, and unless that wood stove room is sweltering, the air at ground level will likely not be above 70 degrees…not really useful for heating.
Also, depending on the size of the duct that services the room with the wood stove, if you blow in there, and the main blower is not operating, you’ll probably just get that air forced down the main supply trunk, through the return, and out the largest return grille, wherever that may be. The air is going to find the path of least resistance.
I’ve owned and used this exact product. While it’s a nice idea, practically speaking it doesn’t work (even for a casual smoker). I’ll provide details on my experience explaining why, if you’d like.
The room isn’t too big (something like 10x15, with a 7 foot ceiling – all the ceilings are low in this house, I think because the forced air heating/cooling was laid over the original flooring sometime in the past 20 years; like I said, terribly designed house, with ad-hoc modifications, one on top of the other).
It’s really not overly generous to assume 78 degree (or higher) air getting piped through: first, I like ambient temperature to be 75 or above; second, the floor vent in the room with the wood stove is only about 5 feet away from the stove; third, the floor vent is between the stove and the “livable” area of the room. The “livable” area usually registers about 75, making the area right near the stove a bit toastier. Piping some/lots of the hot air away before it warms the rest of the stove room might actually be a good thing, as my wife is usually found in that livable area when she’s home, and she doesn’t like it quite as warm as I do.
Lastly, the floor vent in my room is located directly in front of the sliding glass door. Assuming I’m able to get enough heat through the existing ducts, it might essentially take the place of a (weak) space heater. I’d like to think that I can insulate/seal off the exhaust sufficiently; not only am I not too worried about it looking nice, but it’s a relatively temporary thing (only in winter, only for as long as we’re in this rental).
Of course, there are issues, as you bring up:
Granting that I need to have some solution, let’s assume that the best one for my situation can be split into two parts: (1) heat dispersion (an intake blower near the stove and an outgoing blower (sucker?) in my room) and (2) an exhaust appartus (vent the smoke to the outside).
For (1): what should I look for in choosing the blowers? Any recommendations on CFM, dB levels, etc.? What can/should I do to make it as quiet and efficient as possible? Any recommendations on where to buy this equipment cheaply? And finally, how do I determine the operating cost of this setup (electricity usage) versus just relying on the built-in furnace?
For (2): how much air might I expect to have to pump out of the room to strike a balance between heat loss and decent ventilation? It seems like it would be fairly low, but I could be wrong. Is there any way to recoup at least some of the heat contained in the exhaust? I have to say that I’m not really seeing one, without also setting up an intake vent that does some heat exchange.
Thanks for taking the time and effort to respond (everyone); it’s helped clarify my thoughts and provided me options I hadn’t really worked out previously.
