# venting dryer indoors

But evaporating the water takes about 10X more heat energy than you save with a lower thermostat setting.
Nick
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On 14 Feb 2006 05:32:02 -0500, snipped-for-privacy@ece.villanova.edu wrote:

A) This is not a situation where the person is evaporating water just so she can heat the house. The water has already been evaporated, and she wants to gain the side benefit of having that warm air and humidity inside the house.
B) I think your last two lines above are inaccurate. I think it takes 10 or so times as much heat to raise the temperature of water one degreee when the water is also changing from liquid to gas, than it does to raise the temperature of the water one degree without a change of state. But the thermostat setting that is possible with higher humidity is lower by more than one degree. I would say it's possible to achieve the same degree of comfort with the thermostat set 5 degrees lower.
Although it was undesired, I have a lot of experience related to this. When I lived in NY, I had a landlord who fancied himself a plumber. He *was* capable of simple repairs, and of installing water-powered trash compactors, and he had done those things for a living for some years before buying my building and some others; but he was not capable of maintaining the oil furnace steam heat that this 6-story 49-unit building had, (nor did he understand the water pressure issues for a 6 story buidling on a hill.)
Because he fancied himself a plumber, he only called a skilled repairman as a last resort. Consequently, we spent a lot more than the typical number of days each winter without heat. I learned how to "heat", that is, make feel comfortable, my 6-room apartment by boiling water on the stove. Although I don't have numbers regarding how much gas I used to boil the water for an hour (and I don't even remember exactly how long I did so each time) I'm pretty sure the effect on my comfort and my roommates' was far greater by boiling water and increasing the humidity than the same gas would have been just warming the air in the apartment. I believe there were a few occasional stories on the news during the 12 years I lived in NY that specifically said boiling water was far more effective. (and safer because less gas had to be burned.)
Now that I own my own house, I bear a good portion of the blame any time the furnace doesn't work. Never theless, there have been quite a few days like this. I've used the shower (and a stoppered tub, which I watch carefully to make sure it doesn't overflow) to raise the humidity, and it takes no longer than running the furnace (up to a point. I can make the house as hot as I want with the furnace, but increased humdity can only do so much.) Remember to remove the bar of soap before running the shower. I've wasted some soap when I didn't remove it.
I've also boiled water on the stove in this house. I use a pot that holds more than a gallon.
Both methods have had enormous effects on how comfortable I am when the temperature in the house is 65 or 63 or even lower. That is, I feel fine at those temperatures.
The OP only reported condensation on *some* of the windows in her house, that part of the house where the dryer is, and that dissipated quickly.
She doesn't have excess humidity and she's not going to hurt anything.
As to excess lint in the air, I've been doing this for 20+ winters, and I haven't noticed anything. The dryer has a lint filter and my diverter box has a second lint filter, that fills much more slowly than the one in the dryer. Her device has some sort of filter too. I clean my filters and I'm sure she does too.
I've never heard of a house fire where the air burnt because of the lint in it, or where lint in the air was noticed to be burning. I've never heard of a house fire where dust on the furniture or the mantle was listed as one of the causes of the fire, or of the fire's spreading. Maybe CDET22 can refer us to evidence of this.
But I can see the dust in my air when the sun is bright and shining in the window, and it's no thicker in the winter than the summer, when I vent the dryer outside and there is a breeze exchanging indoor air with outdoor air.

Remove NOPSAM to email me. Please let me know if you have posted also.
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Untrue, with the furnace humidifier.

I'm afraid you are incorrect, unless you live in an empty oil tank with no insulation in Barrow, Alaska :-)

Evaporating a pound of water takes 1000 Btu. Raising its temp 1 F takes 1 Btu.

I suggest you try actual numbers, including a house air leakage estimate.
Nick
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On 15 Feb 2006 06:42:49 -0500, snipped-for-privacy@ece.villanova.edu wrote:

But true wrt the OP, which is the person I thought we were talking about. . I did recommed a furnace humidifier, and a lot of other people do too.

That's pretty much what I said, except that I thrrew in a 1 degree rise in temp when it is evaporated. That's just the difference between 9X and 10X.

Air leakage would be a separate issue.
I've been thinking about this more, and I'm pretty sure there were specific statements on the news in NY that the city said that heating the apartment with the stove was dangerous, and that boiling water was safe and much more effective. I've done it many times, and that is my conclusion too.

Remove NOPSAM to email me. Please let me know if you have posted also.
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Wrong, by a factor of 100. Raising a pound of 211 F water to 212 takes 1 Btu. Evaporating the water takes about 1000 Btu. The ratio is 1001:1 vs 10:1.

The calc below shows the thermostat setpoint can only be lowered 0.74 F.

I disagree.
Nick Article 93130 of alt.energy.homepower: From: snipped-for-privacy@ece.villanova.edu Newsgroups: alt.home.repair,sci.engr.heat-vent-ac,misc.consumers.frugal-living Subject: Re: Winter humidification wastes energy Date: 11 Feb 2005 08:33:11 -0500 Organization: Villanova University
Sent: Monday, January 17, 2005 8:58 AM
Subject: Attn: president/legal--Winter humidification wastes energy
Gentlemen,
I suspect that winter humidification wastes vs saves heating energy, and the savings claim is an energy myth. People tend to forget that evaporating water takes heat energy, and that heat energy has to come from somewhere, even if something like a humidifier belt motor uses little energy by itself.
The heat saved by turning a thermostat down appears to be far less than the extra heat used to evaporate water, in all but extremely tight houses with little insulation, eg submarines.
http://lennox.com/pdfs/brochures/Lennox%20WB2-WP2%20Humidifiers.pdf claims that 69 F at 35% RH and 72 F at 19% RH are equally comfortable, but the BASIC program in the new ASHRAE 55-2004 comfort standard predicts that 69 F and 35% RH and 69.7 at 19% RH are equally comfortable (PMV = -0.537, see below.)
If a 2400 ft^2 tight house has 0.5 ACH and say, 400 Btu/h-F of conductance, turning the thermostat down from 69.7 to 69 saves (69.7-69)400 = 280 Btu/h.
Air at 69 F and 100% RH has humidity ratio w = 0.015832 pounds of water per pound of dry air, so 19% air has wl = 0.00301, and 39% air has wh = 0.00617. Raising 69 F air from 19 to 39% requires evaporating wh-wl = 0.00316 pounds of water per pound of dry air. Dry air weighs about 0.075 lb per cubic foot.
With 0.5x2400x8/60 = 160 cfm or 9600 ft^3/h or 720 pounds per hour of air leakage, raising the indoor RH from 19 to 39% requires evaporating 720x0.00316 = 2.275 pounds of water per hour, which requires about 2275 Btu/h of heat energy, so it looks like humidifying this fairly airtight house wastes 2275/280 = 8 times more energy than it "saves." And many US houses are less airtight, so humidification would waste more energy.
Thank you.
Nick Pine
10 SCREEN 9:KEY OFF 20 CLO=1'clothing insulation (clo) 30 MET=1.1'metabolic rate (met) 40 WME=0'external work (met) 50 DATA 69,35,69.74,19 60 FOR CASE=1 TO 2 70 READ TC,RC 80 TA=(TC-32)/1.8'air temp (C) 90 TR=TA'mean radiant temp (C) 100 VEL=.1'air velocity 110 RH=RC'relative humidity (%) 120 PA=0'water vapor pressure 130 DEF FNPS(T)=EXP(16.6536-4030.183/(TA+235))'sat vapor pressure, kPa 140 IF PA=0 THEN PA=RH*10*FNPS(TA)'water vapor pressure, Pa 150 ICL=.155*CLO'clothing resistance (m^2K/W) 160 M=MET*58.15'metabolic rate (W/m^2) 170 W=WME*58.15'external work in (W/m^2) 180 MW=M-W'internal heat production 190 IF ICL<.078 THEN FCL=1+1.29*ICL ELSE FCL=1.05+.645*ICL'clothing factor 200 HCF.1*SQR(VEL)'forced convection conductance 210 TAA=TA+273'air temp (K) 220 TRA=TR+273'mean radiant temp (K) 230 TCLA=TAA+(35.5-TA)/(3.5*(6.45*ICL+.1))'est clothing temp 240 P1=ICL*FCL:P2=P1*3.96:P3=P1*100:P4=P1*TAA'intermediate values 250 P508.7-.028*MW+P2*(TRA/100)^4 260 XN=TCLA/100 270 XF=XN 280 EPS=.00015'stop iteration when met 290 XF=(XF+XN)/2'natural convection conductance 300 HCN=2.38*ABS(100*XF-TAA)^.25 310 IF HCF>HCN THEN HC=HCF ELSE HC=HCN 320 XN=(P5+P4*HC-P2*XF^4)/(100+P3*HC) 330 IF ABS(XN-XF)>EPS GOTO 290 340 TCL0*XN-273'clothing surface temp (C) 350 HL1=.00305*(5733-6.99*MW-PA)'heat loss diff through skin 360 IF MW>58.15 THEN HL2=.42*(MW-58.15) ELSE HL2=0'heat loss by sweating 370 HL3=.000017*M*(5867-PA)'latent respiration heat loss 380 HL4=.0014*M*(34-TA)'dry respiration heat loss 390 HL5=3.96*FCL*(XN^4-(TRA/100)^4)'heat loss by radiation 400 HL6üL*HC*(TCL-TA)'heat loss by convection 410 TS=.303*EXP(-.036*M)+.028'thermal sensation transfer coefficient 420 PMV=TS*(MW-HL1-HL2-HL3-HL4-HL5-HL6)'predicted mean vote 430 PPD0-95*EXP(-.03353*PMV^4-.2179*PMV^2)'predicted % dissatisfied 440 PRINT TC,RC,PMV 450 NEXT CASE
69 35 -.5376486 69.74 19 -.5372599
Engineering VP Mark Hogan said Lennox was embarrassed by all this and he didn't know where their numbers had come from, and he thanked me for bringing this to their attention and said they are changing their printed brochures and Aprilaire web site energy-savings claim.
This reminds me of David and Goliath :-)
Nick
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I want to thank everyone for the responses. I had hoped to generate a discussion but had not anticipated such a divergence of opinion. My overall impression is that my actions may have some merit as long as my dryer use is not excessive. We probably do a couple of loads every other day. Of course I considered safety issues before diverting the vent indoors and decided it posed no threat since the dryer is no more than a large electric heater with a blower fan. My plan is to try it for a while and keep a close eye on things. If the indoor humidity becomes excessive or lint becomes a problem, I can simply reattach the hose to the pipe venting outdoors. I plan to do this in any event as soon as the weather warms up and it is my hope is that winter does not linger for long here on the US eastern seaboard.
Also, thank you all for the suggestion on alternate ways to dry clothes as well as other energy saving tips. Unfortunetly I am stuck with what I have right now and will try to make the best of it. Sooner or later I know I will need to replace my dryer and I will need to decide whether gas or electric dryers are more efficent and cost effective at that time. I suppose I will cross that bridge when I get to it. Thanks again.
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I am a Certified Dryer Exhaust Technician. Most building codes require that the dryer vent to the exterior of the structure due to fire hazard issues. To say that "the dryer is no more than a large electric heater with a blower fan" does not take into account the highly flammable lint that is in the mixture. With the vent terminating inside, the lint content of the air is increased and the home's air becomes a tinder box that can ignite/explode with the right circumstances. Is this a good trade-off for some heat reclamation? It's your home. You decide.
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Well, this last post got my attention. I have never heard of a "Certified Dryer Exhaust Technician" and didn't know there was such an animal but I will take your word for it (that's just the kind of person I am). The last thing I want to do is create a hazard in my home in order to save a few bucks. As I have indicated I have a bucket of water trapping most of the lint but before I abandon my venting scheme I am going to have to do a little more research on the dangers of lint in the air. If this is such a danger I wonder why you can purchase a kit specifically made for venting a dryer indoors. Wouldn't that seem counterintuitive.
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The kits that are available that vent to a box specifically state that they are to be used ONLY IF an exterior termination point is not possible. Dateline NBC did a story about the fire hazards involved with clothes dryers and their lint. The "blow torch" effect suggests a constant flow of fire. The lint burns quickly and the amount of new lint fed to the flame is not enough for a "blow torch' effect. The cubustible air content requires a high concentration of lint in a closed-in area and a flash-point. This is possible with continued use of an internally vented clothes dryer. BTW, the Certified Dryer Exhaust Technician credential is awarded by the Chimney Safety Institute of America.
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