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  1. #1

    Question Lowering humdity levels

    I live in a home deep in a coastal redwood forest in Northern California.

    The weather in the summer is dry and warm. For around a quarter of the year it drops to 45-55f and rains a lot often constantly for weeks.

    The home is heated with forced air a new 97%-efficient furnace was installed last year and a wood-burning stove, which we use most winter evenings. (There's no need for air-conditioning in the summer.) I work from home, so the temperature inside is never below 67f during the day. We lower the thermostat to 55f at night, though the temperature doesn't often drop below 60f.

    Humidity levels inside are routinely between 55% and 68% in both the summer and winter. Most mornings in the winter, we wake to (really) dripping windows, especially in the north-facing bedroom which doesn't get any direct sunlight for a few months of the year. The windows are quite old aluminium-framed models.

    In order to try and reduce the indoor humidity levels, we're investigating adding a whole-house dehumidifier to the HVAC ducts.

    One contractor has suggested an ERV instead, though as the winters are colder and very wet, I'm not sure this would help.

    Any suggestions for solving the humidity and condensation problem? Would a whole-house dehumidifier help in this climate? Is an ERV a viable solution?

    Thanks in advance,

    Russell.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,446
    Yeah a whole house dehu should be able to keep below 50% rh and you can bring in outdoor air for better indoor air quality. Look up teddy bear's posts in the search engine on this site, he's real knowledgeable about dehus. Check out ultra Aire and santafe dehus they're super efficient at moisture removal.

  3. #3
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Is your home built on a slab?

    IMHO an ERV would be a more efficient option and may do the trick about 75% of the time.

    One thing you really need to do is tighten up the whole home. Your leaky, drafty non insulated windows are causing you more harm than anything else.

    If the home is built on a slab, you will find this problem really difficult to remedy, I have a friend that lives in the mountains of Arcata and we added radiant floor heating and he is using a solar water heater to do most of the work. This solved virtually all of his humidity problems and made the home much more comfortable. not to mention cut his energy usage in half.

    Look in to windows, sealing up the doors and potentially more insulation first, most insulation contractors will promise you the world, but I would look into that before I did anything else.

    Good luck.
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  4. #4
    Join Date
    Nov 2012
    Posts
    31
    Quote Originally Posted by GT Jets View Post
    Is your home built on a slab?

    IMHO an ERV would be a more efficient option and may do the trick about 75% of the time.

    One thing you really need to do is tighten up the whole home. Your leaky, drafty non insulated windows are causing you more harm than anything else.

    If the home is built on a slab, you will find this problem really difficult to remedy, I have a friend that lives in the mountains of Arcata and we added radiant floor heating and he is using a solar water heater to do most of the work. This solved virtually all of his humidity problems and made the home much more comfortable. not to mention cut his energy usage in half.

    Look in to windows, sealing up the doors and potentially more insulation first, most insulation contractors will promise you the world, but I would look into that before I did anything else.

    Good luck.
    Would an ERV get the humidity out as well as a dehumidifier? If with an ERV you can bring fresh air plus dehumidify why not install that in every occasion rather than getting a dehumidifier?

  5. #5
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Quote Originally Posted by wak View Post
    Would an ERV get the humidity out as well as a dehumidifier? If with an ERV you can bring fresh air plus dehumidify why not install that in every occasion rather than getting a dehumidifier?
    Not as well as a dehumidifier by a long shot, but the area the OP is talking about experiences a lot of cold rain, not warm rain like in the east...

    If the air is cool and the house is warm, an ERV will work more often than not. Look up a psychrometric chart and see why it works, use a test like 40 degrees F at 100% humidity with a 68 degree F room temperature... You'll find that the end result for humidity will end up in the 50% range.

    Wont work well in the deep south or the eastern united states.

    Hoping this answers your question.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,534
    Quote Originally Posted by russellq View Post
    I live in a home deep in a coastal redwood forest in Northern California.

    The weather in the summer is dry and warm. For around a quarter of the year it drops to 45-55f and rains a lot often constantly for weeks.

    The home is heated with forced air a new 97%-efficient furnace was installed last year and a wood-burning stove, which we use most winter evenings. (There's no need for air-conditioning in the summer.) I work from home, so the temperature inside is never below 67f during the day. We lower the thermostat to 55f at night, though the temperature doesn't often drop below 60f.

    Humidity levels inside are routinely between 55% and 68% in both the summer and winter. Most mornings in the winter, we wake to (really) dripping windows, especially in the north-facing bedroom which doesn't get any direct sunlight for a few months of the year. The windows are quite old aluminium-framed models.

    In order to try and reduce the indoor humidity levels, we're investigating adding a whole-house dehumidifier to the HVAC ducts.

    One contractor has suggested an ERV instead, though as the winters are colder and very wet, I'm not sure this would help.

    Any suggestions for solving the humidity and condensation problem? Would a whole-house dehumidifier help in this climate? Is an ERV a viable solution?

    Thanks in advance,

    Russell.
    Basics:
    Ocuupants add moisture to the air in a home. The air in a home is outside air that is slowly passing through the home. During calm wind and moderate temps, air changes declines to near nothing.
    The real moisture content of air is the dew point of the air or the grains of moisture per lb. of air. An occupant adds .5 lbs. of moisture per hour. When there is no air change, one lb. of moisture raises a 2,000 sqft. home 5^F dew point or about 5%RH. Several hours of low/no air change will evelate the indoor moisture levels. Homes need an air change in 4-5 hours when occupied to renew oxygen, purge the indoor pollutants, and moisture. Adequate air change reduces the increase of indoor moiture levels. The more air that passes through your home the less the home's dew point is elevated above outdoor dew points.

    ERVs blow a controlled amount of air in and out of a home. They transfer a portion of the heat and moisture from the wet air to the dry air based on %RH. ERVs are not dehumidifiers. If the air being blown out is damper than the fresh air being blown in, moisture is transfered into the fresh air entering the home. NOT IDEAL during some of the conditions for your application because of the wetting effect. There are occasions when they help but are not a good solution.
    When the indoor dew point is about 10^F above outside dew point, you are probably getting enough fresh air to purge indoor pollutants and renew oxygen.
    Now back to the real problem, Sweaty Windows. Any surface that sweats is below the dew point of the air in your home. The measured temperature of a metal container full of water slowly cooled until the surface has condensate, accurately tells you the dew point of the air. This works inside or outside. Your single pane windows are cool and therefore prone to have condensate.
    What to do? A good dehumidifier will keep your home <45% RH (<45^F dew point). In all but the coldest weather, the windows will not sweat. With 2 occupants in 1,500 sqft home, if your indoor dew point is <10^F above outdoor dew point, you have enough fresh air. If the dew point is +10F above outside, you would benefit from adding make-up fresh air ventilation during calm weather. An Ultra-Aire whole house dehumifier with the ventilation option would solve all of the problems. Someday replace the windows. Another benefit of maintaining <50%RH is eliminating mold and dust mites in the home.
    Sound complicated? Get the whole house dehumidifier and use the fresh air option during calm weather. A good HVAC contractor with instructions from the factory can install the system.
    Keep us posted.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #7
    Is your home built on a slab?
    No, it's actually on a slope, on stilts. The top side is around a foot away from the ground, the lower side is around 9 feet off the ground. So the "crawlspace" is open and ventilated. The subfloor has insulation, although it probably needs replacing as it's old and not in good shape.

    ERVs blow a controlled amount of air in and out of a home. They transfer a portion of the heat and moisture from the wet air to the dry air based on %RH. ERVs are not dehumidifiers. If the air being blown out is damper than the fresh air being blown in, moisture is transfered into the fresh air entering the home. NOT IDEAL during some of the conditions for your application because of the wetting effect. There are occasions when they help but are not a good solution.
    When the indoor dew point is about 10^F above outside dew point, you are probably getting enough fresh air to purge indoor pollutants and renew oxygen.
    Now back to the real problem, Sweaty Windows. Any surface that sweats is below the dew point of the air in your home. The measured temperature of a metal container full of water slowly cooled until the surface has condensate, accurately tells you the dew point of the air. This works inside or outside. Your single pane windows are cool and therefore prone to have condensate.
    What to do? A good dehumidifier will keep your home <45% RH (<45^F dew point). In all but the coldest weather, the windows will not sweat. With 2 occupants in 1,500 sqft home, if your indoor dew point is <10^F above outdoor dew point, you have enough fresh air. If the dew point is +10F above outside, you would benefit from adding make-up fresh air ventilation during calm weather. An Ultra-Aire whole house dehumifier with the ventilation option would solve all of the problems. Someday replace the windows. Another benefit of maintaining <50%RH is eliminating mold and dust mites in the home.
    Sound complicated? Get the whole house dehumidifier and use the fresh air option during calm weather. A good HVAC contractor with instructions from the factory can install the system.
    Thanks a lot for this!

    Firstly, a note: the windows are actually double-glazed, not single-pane — though the seals have gone on a couple of them.

    Secondly, a few questions if you have time to answer:

    * Is there any difference between the Ultra-Aire 100V and XT105 aside from form factor and efficiency? (looking at: http://www.thermastor.com/Ultra-Aire-UA-100V/)

    * If ducted into the heating, what effect does a dehumidifier have on heating costs? (If the air is being refrigerated each time before getting back to the furnace...)

    * Same question, but regarding the ventilation option?

    Thanks again for your advice,

    Russell.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,534
    Quote Originally Posted by russellq View Post

    Firstly, a note: the windows are actually double-glazed, not single-pane though the seals have gone on a couple of them.

    Secondly, a few questions if you have time to answer:

    * Is there any difference between the Ultra-Aire 100V and XT105 aside from form factor and efficiency? (looking at: http://www.thermastor.com/Ultra-Aire-UA-100V/)

    * If ducted into the heating, what effect does a dehumidifier have on heating costs? (If the air is being refrigerated each time before getting back to the furnace...)

    * Same question, but regarding the ventilation option?

    Thanks again for your advice,

    Russell.
    The xt105 is our latest version of a whole house dehu with the highest eff. rating any dehu made. It is horizontal verses vertical.
    Regarding the impact on the home, the dehumidification process yeilds more heat than energy consumed. This is because each lb.of mositure removed provide 1050 btus of heat. The end result is that you get about 10,000 btus of heating for each KW used. This is like a heat pump COP of +3. This very efficient heating. Of course when cooling, this works against you. However warming air in a home also reduces the %RH at the rate of -2.5%RH per degree of rise. The XT105 is the finnest unit we make.
    Keep us posted.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #9
    Ah, we don't have cooling, only heat, so all sounds good. The home is actually only 1,450 sq ft, so the 70H seems to be the best fit.

    Now I just need to find someone out here to install it!

  10. #10
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    Quote Originally Posted by teddy bear View Post
    The xt105 is our latest version of a whole house dehu with the highest eff. rating any dehu made. It is horizontal verses vertical.
    The XT105 is the finnest unit we make.
    Keep us posted.
    Regards TB
    We installed an XT105 2 weeks ago, and I have to say, it is a nice machine. It is very quiet, and did the trick for a very picky client who had reservations about it's noise level, and ability to maintain his home at 46% RH. Just talked with him yesterday, and his feedback was very positive regarding everything about the unit, especially the reduced RH in his home, which maintains 46%.

    Just thought I'd share.

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