Replies

1. 
   David_Thomas | Jan 10, 2001 08:44am | #1

   *
   No.

1. 
   David_Thomas | Jan 10, 2001 08:54am | #2

   *Or at least there shouldn't be. Because many dryer installations are marginal in getting the air, CO2, CO, and lint out of the house through the circuitous duct work even without adding the restriction of a HX that will clog up with lint.If you want to do one yourself and will keep it cleaned out, you could start with a "stack robber" designed to get more heat out of a wood stove flue pipe (also a questionable pursuit) and a booster fan so there is enough pressure to keep the air moving. But you have two inherent, opposing design goals. One is free-flowing air to keep the lint moving. The other is maximizing surface area and minimizing passage size to increase heat exchange. All in a package that is easy to service on a regular (weekly?) basis.I'd focus on recovering the sensible and latent heat from your bathroom fan first. It allows you to dabble with the problems of moisture buildup (Legionaire's Disease, etc.), icing, and achieving equal and opposite flows.When that's working well, move on to the dryer with the added problems of combustible lint (had an uncle whose house burned down from lint in the dryer), cleaning the HX surfaces, and posionous carbon monoxide.I do understand the urge to save energy and to tinker. I suffer from them too. But if you look beforehand, there may be better places to leap. -David

1. 
   Freelance_ | Jan 10, 2001 05:08pm | #3

   *David- I don't think the question is that easily answered. Is the dryer gas or electric? Mine is electric so I've only lint and moisture to deal with. I live in a dry climate, so with our frequency of use, in a house of our size and characteristics, the moisture added to the interior is no problem. Moderately effective secondary lint traps are available. The fine particulates that do end up in the air are caught by the HEPA filter. This allows us direct use of the dryer exhaust for space heating. Our secondary lint trap is cleaned every other cycle or so. All things considered, the 200 cfm the dryer pumps out would cause substantial issues to arise if exhausted to the exterior.An electric dryer with secondary lint filter exhausted into a home with filtered air and a hygrometer to monitor effects should not be dismissed so quickly. We wash clothes in the evening. They go into the dryer when the coffee goes on. The house warms quickly, then we go to work. If we ran the dryer, took showers, boiled pasta and washed the dog all at the same time we might imbalance things. A thoughtful approach allows a certain latitude in certain latitudes.What I mean is, I think we need to know substantially about keith before we can accurately address his query.Warmly-Lance

1. 
   Art_B | Jan 10, 2001 05:33pm | #4

   *I vent my electric dryer straight into the basement thru a 8 by 16 furnace filter. Lint is no problem, there is always more sawdust than lint in the basement, even without a secondary lint filter and the dust collector running. Wife hangs laundry outside on the line when weather is warm such that indoor humidity would be a problem. (Pac NW)Gas dryer in Cent. IL case history -unused flue from old coal furnace used for vent, it has an existing masonry heat exchanger (bet one of those would cost a bundle to build today if anybody remembers how), always had a warm wall in the kitchen above when drying clothes. As Dave says, CO/CO2 can be a problem as that installation's biggest problem (before putting screen over flue) was squirrels warming themselves, passing out, then falling in.

1. 
   David_Thomas | Jan 10, 2001 07:41pm | #5

   *Freelance and Art: I agree that with an electric dryer, it is quite doable. My mistake for focusing on the gas dryer only. (If I want heat, I burn fuel. I only use electricity for lights and motors.) It would cut of the cost of the electricity in half as you are using it twice - to dry the clothes and to heat/humidify the house. Gets it down to being only 3 times as expensive as natural gas. (Your mileage may differ.)But for a gas dryer, I stand by my original cautions. It is so important to get flue gases out of the house that I'd want someone to a mechanical engineer AND a plumber or a vhemical engineer AND a HVAC guy before experimenting on some new way to do it.Art: How often do you need to change the furnace filter? -David

2. 
   Art_B | Jan 10, 2001 10:01pm | #6

   *Dave: It has never been changed unless damaged (>20 yrs). The lint gets heavy enough to peel off like a piece of felt, similar to the stuff on the dryer screen, my dad just uses a piece of window screen for the secondary filter. It is against concrete, so nil fire hazard -don't think I would do it with gas dryer. I have heard of gas dryer fires from lint accumulation in the dryer vent itself when vent has a "dip". Redundant cutoffs in elec. keep temp under 250F, well below lint ignition. My mileage (suburban Seattle) is such that the heat pump is cheaper than gas until below 20F. (7cents kwHr, 75 cent/therm or so nat gas - I don't have gas, 2 houses in my wife's old neighborhood burned down due to nat gas fires , CH4 scares her like heck)

3. 
   Frank_H._Biscardi | Jan 11, 2001 12:01am | #7

   *When I was a kid and my Dad was out of work we tried heating the house by putting a nylon stocking over the dryer vent tubing. The windows and wall dripped water. We were marginally warmer.I wouldn't do it.Frank

4. 
   FredB | Jan 12, 2001 07:55am | #8

   *If you use a heat exchanger you would need to somehow handle the condensed moisture so it wouldn't puddle and corrode. There will be condensed moisture when the warm air meets the cold. Seems to me for the little amount of heat you gain compared to the cost of the exchanger and its' maintenance over the years this isn't a very good idea. Plus you will be interfering with dryer efficiency and that will raise costs.This is similiar to the old idea of stack robbers on oil furnaces/boiler. They did reclaim heat. But they corroded, mechanically interfered with stack air flow reducing efficiency and, worst of all, lowered stack temperatures to an unacceptably low point. Could make a lot more money redesigning the burners.

5. 
   Tim_H | Jan 13, 2001 12:17am | #9

   *I have heard via indoor air quality workshops that the dryer sheets like "bounce" are a significant and very ugly source of air pollution. Sure don't want that crap along with all the excessive moisture and lint in my home.

6. 
   David_Thomas | Jan 13, 2001 05:12am | #10

   *Art: I saw the work of an artist up here (actually in Homer) and the material looked very familiar although I could place it. It was dryer lint, used like felt. It was in mnay different colors (from various terry cloth towels?) Very eco-groovy in the reduce, reuse, recycle vein. And it smells better when wet than the another artist's work up here - she knits hats from dog hair.Your dad's success with the filter speaks to the advantage of large surface area. Even as it cakes (felts?) up, there is enough surface to let the exhaust through.At 8.3¢/kwh and 38¢/therm, my gas bill ($40 in winter) is less than my electric ($90), but then we use a lot of lights for mental health reasons up here. And have a very tight house.FredB: I forgot about the carbonic and sulfuric acid in my list of cautions. So in addition to all the other design constraints, it's gotta be constructed from stainless and high temperature plastic?!Tim: What's the nastiness in Bounce? Can't be too exciting because I haven't heard of anyone abusing it like they do gasoline, propane, spray paint, glue, etc. -David

7. 
   Tim_H | Jan 13, 2001 08:47pm | #11

   *DavidCan't remember the specifics, But it was told to me by a cold climate housing guru from Univ of Ak, Fairbanks. The course was free and offered by the local extension service. Seems to me it was teleconfrenced to Anchorage . Maybe they will do it again and it will be available in your neck of the woods. The instructor said the dryer sheets were very nasty. Sorry but you are gonna have to stick to the contact cement ,gas routine for a buzz. everything that is bad for you doesn't have to give you a high, some are just bad.You got any snow down there ? might have 6" up here. Hope it doesn't rain

8. 
   David_Thomas | Jan 13, 2001 09:23pm | #12

   *Tim: Was that John Zarling from UAF? I'll try dropping him a line - I took my Arctic Engineering course from him and two UAA guys. They do a 1-day, homeowner roadshow version and have offered it at the community college in Soldotna. We've now got enough snow to ski on (4") on unplowed roads. Not hardly enough to go off-trail yet. They're dogsledding in the Caribou Hills to the south now, finally.

9. 
   Tim_H | Jan 14, 2001 10:43pm | #13

   *DavidNo John Z. doesn't ring a bell . I think it was Rich Siefert. Went to a dog pull yesterday in Eagle River, it looked like they brought in snow for it.chinook winds and 35 last night

2. 
   keith_williams | Jan 14, 2001 10:43pm | #14

   *
   IS THERE AN AIR TO AIR HEAT EXCHANGER DESIGNED TO PREHEAT INCOMING FRESH AIR WITH OUTGOING DRYER EXHAUST?