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  1. #14
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    Originally posted by amd
    It's called relative humidity for a reason. Heating systems do not remove moisture - they simply increase capacity of it.

    30F outdoor air is @ 60% RH is very dry when heated to room temperature for example. Newer homes have much less infiltration relative the moisture produced by occupants.

    Homes with natural draft furnaces tend to be much drier - outdoor air has to displace what goes up the stack.

    I would have thought that all hvac technicians grasp the concept of relative humidity. Guess not.



    [Edited by amd on 10-27-2005 at 08:13 PM]



    still does not explain why hot air furnace dries house out more than hot water boiler. both draft up chimney.

  2. #15
    Join Date
    Aug 2001
    Posts
    1,936
    if you dont have storm windows try putting one in and see if it helps with that one window

  3. #16
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    Originally posted by Edmund Forsthe
    if you dont have storm windows try putting one in and see if it helps with that one window

    O P stated 55-75% humidity, don't think its a window issue.

  4. #17
    Join Date
    Jun 2004
    Posts
    8
    Thanks to everyone for the replies thus far...

    To answer the questions I saw: Yes, there is a 30pint dehumidifier that's been on for a few days (I think 4 days this year...but I tried the same one for awhile last winter too)...it fills and needs to be emptied, but it seems to have zero effect. I don't know much about dehumidifier capacity, but I think it's rated for a house about 1/4 sq ft of mine (when you include my basement)...

    There was another comment about opening a door for ventilation. I actually tried that last year...and a window...the issue of course is that quickly I get a very cold house (I did this on the worst days - it was probably 1 degree out)...no matter how much heat I seemed to waste, it didn't seem to have much of an effect (if any) on the window condensation...

    Thanks again, looks like the repeating suggestion is to get an HVAC guy in to look at bigger humidifier or some type of ventilation system...

  5. #18
    Join Date
    Oct 2005
    Location
    Quincy, Il
    Posts
    24
    tinknocker, not dumb. I was thinking the same thing. should have a tech check it out, and if there is a humidifier have them install a humidistat.

  6. #19
    Join Date
    Apr 2002
    Posts
    11,808
    The first winter after new construction there is moisture, but ventilation should take care of it. The ventilation would work hard the first winter.

    Dehumidifiers are designed to work the best in summer time, they will not be effective when you need to be pulling the RH down in your house to be low enough to stop window condensation in the dead of winter.

    You seem to realize that cooking and showers create humidity, and as a dumb sounding suggestion, make sure you are not hang drying laundry in that big basement.

    I would assume that there is a vapour barrier under the basement floor slab. Easy test would be to place a pail on the slab, go back a day or so later and pick up the pail and see if there is a ring of moisture under it.

    Most likely you need to ventilate, exhaust some humid air and replace it with cold dry air to dry out the home.

    For a house your size you would need a system capable of moving 180 to 200 CFM. This ventilation system could be controlled by a dehumidistat to turn on when RH rises. The setting will depend on how cold it is outside and how good your windows are. I would initially try a 35% setting once the outside temp falls below freezing.

    If the system maintains 35% and there is still condensation, then lower the setting. You may find that a higher setting of say 40% will work as well. This depends on the quality of your windows.

    Your house sounds fairly tight so exhausting a large amount of air could make chimnies spill. You should make a provision for a way for air to get back into your house.

    Exhaust fans with a make up system will work. The Humidex mentioned by others are just a packaged exhaust fan.

    Our group's leading dehumidifier salesman has recently suggested a good test and I am going to plagerize him here and now. Since it is not overly cold out right now, crack open a couple windows and run the clothes dryer on 'air fluff' for a few hours and see if RH starts to drop off. Other wise try a couple bathroom fans continuously for a day or so. Do this when it is in the 40s outside.

    You mentioned that you opened windows before and were concerned about all the cold air at 0F. You may be interested in a heat recovery ventilator or HRV as pecmsg
    has already suggested. This is a successful system used in Canada and other northern states.

    This system exhausts humid indoor air through a heat exchanger, and at the same time it draws in cold dry air from the outside. The exhaust air heats the fresh air and recovers 60 to 70% of the heat that would otherwise be going straight outside.

    In your case if it was 0F outside and 70F inside, an HRV could recover 65% of the heat you are exhausting.

    There is a 70 degree temperature differential between indoors and outdoors so the system could recover 70 x 0.65 = 45.5 degrees. The fresh air coming into your house would get heated from 0F to 45.5 degrees, so your heating system would not have to work so hard to compensate for the ventilation.

    Another fine edit as I really need to use spell check and the 'preview post' option more frequently





    [Edited by Carnak on 10-28-2005 at 01:24 AM]
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  7. #20
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,289
    Originally posted by deejoe
    check out HUMIDEX. An installation of a Humidex may solve your problem instead of using an electricity guzzling de-humidifier. The Humidex uses approx 35 watts.
    http://www.humidex.ca
    "
    WHAT YOU GET WITH YOUR HUMIDEX:
    10-year warranty on all parts.
    Lifetime warranty on cabinet (against rust or corrosion).
    Vented outside like a dryer no heavy buckets of water to pour out, no filters to change or wash.
    Installation time 1 to 2 hours, complete with assembly kit and instructions. Quiet operating fan (55dB).
    Powerful - able to process 205 cfm (independent lab test)."

    WHAT YOU GET is
    a SIGNIFICANT, additional ~20% heat loss ! ...
    Q = 1.08 * dT * CFM
    __= 1.08 * 40 * 200 = 8640 BTUh

    REAL cost $200 annual +
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #21
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,289

    Lightbulb Sounds Impossible

    Originally posted by battman
    Last winter was my first winter in the house, and there was a significant amount of condensation on the windows when the outside temperature dropped below 35F. At 0F, I would experience dripping levels of condensation from all windows.

    When I called my builder (the house was then under warranty) I was told it was just the new house drying out, and to turn on my furnace fan (to run at all times) and run all ceiling fans/bath vents/etc. Additionally, I bought 2 humistats, and found the humidity levels to hover in the 55-70% range throughout the house.

    So winter #2 is starting, and the Wisconsin weather has had a few nights in the 30's, and again I'm experiencing some condensation on the windows...not dripping yet...but it's also not that cold yet. My humidiy levels are holding between 55 and 75% depending on cooking/showers/etc.

    Again, sorry for questions outside of the norm, but thanks for the advice. Jeff

    " ... found the humidity levels to hover in the 55-70% range throughout the house. "

    FIRST, Turn the HUMIDIFIER to OFF.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #22
    Join Date
    Jul 2004
    Posts
    322
    Newer homes are well sealed and this can create condensation problems. My solution was to crack the door to the attached garage and crack a door upstairs that leads to the attic. The garage air is warmer than outside air, and the attic by design has slight negative pressure. This brings the humidity down without making it too cold or having to run any fans.

  10. #23
    Join Date
    Feb 2004
    Posts
    2,597
    Originally posted by fat bob
    My solution was to crack the door to the attached garage and crack a door upstairs that leads to the attic. The garage air is warmer than outside air, and the attic by design has slight negative pressure. This brings the humidity down without making it too cold or having to run any fans.
    that could work, but be careful with the gasses being given off in the garage such as CO from the vehicles, the gas vapors from the gas can, the lawn boy tank, fertilizers, etc...



  11. #24
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,440
    High humidity indicates inadequate fresh ventilation or an excessive moisture source. Homes naturally ventilate much more during cold weather than warm weather because of the "Stack Effect". Most new homes do not get the necessary 75-100 cfm of fresh when occupied throughout the year. Fresh air renews oxygen, purges pollutants, dries the home during cold weather, and wets the home when the outdoor dew points are +55^F. As the cold season approaches, retained summer moisture must be removed to avoid condensation on cool surfaces like windows. Because the moisture level must be reduced to <35% RH(<35^F dew point) and dry fresh air is readily available, ventilation is more practical than dehumidification. Initially, several hundred gallons of water that must be removed via ventilation from the damp materials in a house. After intial Fall dry down, normal fresh air ventilation will remove the 24 lbs./day of moisture generated by a typical family. Therefore, crack some windows for a week or two during low dew point weather in fall to remove excess summer moisture. The ventilation rate should be like a couple good bath fans. If 75-100 cfm of fresh air ventilation doesn't keep your home dry, find the excess moisture source or increase the ventilation rate. Supplmenting a homes natural leak rate to remove normal moisture cost less than $100 per year of heat with NG or heat pumps at <8,000 heating degree days.
    Homes need more supplement ventilation during the warm times of the year for IAQ. In green grass climates, this must include supplemental dehumidification to avoid the wet home in Fall. This issue is the guts of Indoor Air Quality in a healthy home. TB

  12. #25
    Join Date
    Oct 2005
    Posts
    1
    Wow, I see great contradiction in these answers. The problem for the question is weeding out right from wrong. Your home clearly is too tight. Alot of new construction is built with energy efficiency as the number one priority. My number one concern would be your indoor air quality from not getting enough air changes. As stated in some answers you should install a HRV not only for your condensation problem but also for your families over all health...I would hope any professional HVAC person would understand that Air Conditioners dehumidify not heating systems. If I took a cube of air and raised its temp without adding or removing moister the RH% will drop. If you do the oppostite it will rise. Look in a book at a enthalpy chart. Warm air funaces carry air accross a very hot heat exchanger causing the air to heat more rapidly without adding moisture causing a graet drop in RH%. That dry air is forced around the home and accross peoples bodys. In alot of cases it is an illusion that the forced air homes RH% is lower, compared to hydronic, it is the simple fact that the air being forced around is grabing whatever moitser it can get, skin is a great place for that air to pick up moister......Get a HRV and your small increase in energy cost will be off set by co-pays and missed work from getting all those extra colds this winter. Hope that helps.

    [Edited by bokani on 10-29-2005 at 10:00 AM]

  13. #26
    Join Date
    Jun 2004
    Posts
    8

    one little twist...

    I was planning to call an HVAC guy today but while poking around yesterday, I found something that seemed worth bringing up...

    From what I can tell, there is no air inlet to the furnace - save the one that is on the outside of the house. This consists of a 6 (or 8?)" round duct pipe with an angled inlet cover. Presumably the air enters here, goes about 15' straight into my basement, enters a large chamber made of thin sheet steel and the I beams in my basment ceiling, turns 90 degrees and goes about 30' to the furnace.

    But here's the thing, If I'm outside my house and I look into the air inlet, it's blocked. There's some sort of butterfly looking valve blocking all incomming air.

    So I removed a section of the basement duct near the butterfly valve and looked at it. It's a purely mechanical valve made up of 2 flaps which pivot along the center of the round duct and seem to fold inwards (so incomming air (or a vacuum from the furnace?)) would cause them to open, allowing air in. Only, mine is stuck. It actually looked like it was painted shut...as there was a lot of 'overspray' on the foam gasket that helps make the butterfly valve seal. So, some questions:

    I assume this isn't supposed to be stuck?

    After I 'unstuck' it, I've run my air conditioner, heat, and just fan and looked at the valve under all 3 conditions...it doesn't move/change...and remains just slightly open (which is how it looked after I 'unstuck' it. So it doesn't seem to pivot very well. Assuming this has been stuck for the 2.5 years since the house was built, could it be broken?

    It is feasible that my furnace has been pulling air from the basement(through duct joints, etc) for the past 2.5 years - so it didn't matter that I had a stuck inlet valve (although it would certainly explain some of the moisture)?

    Thanks for all of the replies! Jeff

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