Hello, I was wondering if there is magic ideal number for humidity in a home.
Our house was built in 1924 in the NW with basement main floor and attic converted to 2 bedrooms. I doubt its very tight.
In the basement is a Carrier 98 percent effecient variable furnace The air intake is on the main floor on the side of a gas built-in fireplace in the dining room. Its almost centered in the home next to the basement stairs.
I brought a humidity gauge inside that read 60, now in the house reads 50.
Thanks for any insight.
Replies
"In the basement is a Carrier 98 percent effecient variable furnace The air intake is on the main floor on the side of a gas built-in fireplace in the dining room. Its almost centered in the home next to the basement stairs."
Are you talking about the COLD AIR RETURN or the combustion air for the furnace.
For a high eff furance either has a pipe to bring in outside combustion air or an option for it. To get the most eff out of one outside air should be used. Otherwise you are using condition air to burn and send out the flue.
And 98% eff sounds high to me. Seem that the highest that I have seen is around 94-95, but I might be wrong.
IIRC the max recommended humidity is 60% with 30-50 prefered.
RH for people is more comfortable between 30% and 40%
But that can cause problems with the house. You will see materials move, windows condense, mold and mildew party down...
The house itself will be happier just below 20%
so you will have to strike a compromise with the house.
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>RH for people is more comfortable between 30% and 40%
>But that can cause problems with the house. You will see materials move, windows condense, mold and mildew party down...How do you figure? With constant humidity levels, things don't move. Big fluctuations cause that. And by all other accounts, mold/mildew aren't inclined to grow beneath 50%. I keep 35-45 year round and have no expansion/contraction of floor, furniture, doors, have no condensation, and have absolutely no mold. And by keeping away from a too-dry 20, we have no static shocks either.I advise clients to aim for 30-45.
In your area, there is much greater humidity outside most of the year, so you are far better with it as you report.The breakover point is 40% where mold beginns to grow. below 40% and it will not grow. Kick it up to 45% and it will grow faster.
But we are not necesarily talking apples and apples either. RH is a measure of the percent of moisture the air at a given temperature is capaable of holding. The actuall amt is based on what the temp is at the time.But the references for mold growth are based on percent of volumn by weight...any time you have a dusty surface or other food for the spores to grow on such as bare wood, and surface condensation, the water content of
that immediate surface or material
is definitely greater than the 40% that makes mold happy and hangs out the welcome sign.
See how the RH of the overall air and teh moisture content of the mold growing medium are not exactly the same?Since your temperature differential between in and out is less extreme than up north here, you probably have less condensation with RH of 40% inside than we do at the same. The condition of cleanliness also will make a difference. A clean painted surface in a home where the air is swept by filters in the HVAC system will grow less mold than a bare wood surface in a home heated by wood or where it is cleaned less often. The dust is afood for the microbes Add the water of condensation and you have invited it to start. Keeping the RH below 40% will mean you have less condensation on surfaces. Every home where I have checked out the complaint of too much condensation on windows is one where humidifiers are in use and the RH is above 40%
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I forgot to confirm - yes, IF you keep the humidity constant, and the temp, the materials will not move.
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The model Carrier is a Weather Maker Infinity. I guess I exagerated the 98%, more like over 90%.The Return Air Grill is in the Dining room, but I don't think any other outside air is supplied to the furnace.When I got home this afternoon, the outside air temp was 50 and the humidity inside read 36, and the inside house temp is 67. I don't know how inaccurate the gauge reads.The air feels dry inside.So what average number do you thinks would be ideal? Thanks for the insight
If you have a dehumidifier, set it for 35 - 40%
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its usually about 100% humity outside. I would love to get 50% humity. 2+3=7
I don't have one. Do I need one?
Right now my digital gauge is reading 20%, my cheap Harbor Freight analog is reading 30%, and the more expensive unit I borrowed from work is reading 30%. That's about where it's been all winter inside.
Whenever I pet the cat, I'm constantly zapping him, and I noticed a while back that my hardwood floors are showing significant gaps.
During the summer, I set my dehumidifier to 60%, but I think it's actually dropping it below that-- will have to take some better measurements. At that level, I don't have a musty smell in the finished part of the basement (carpet starts to get an odor when the humidity starts to climb), and the water pipes in the unfinished part of the basement don't sweat. I don't have any water problems in the basement, just that it's enough cooler down there that it drives up the RH.
Since the dehumidifier drives up the electric bill a good $40 during the heavy use months (August & Sept., usually), I try to set it for as high an RH as I think I can get away with.
I guess the question is whether the absence of smell and pipe sweating is an accurate enough indicator that the RH is low enough to prevent long-term mold/mildew buildup.
Don
You don't say where you live or how cold it is out.
No home built in 1924 would be able to have 60 percent humidity inside with the outside temp below about 30F, so I'm guessing that it's much warmer than that.
The normal "ideal" wintertime humidity is around 30-40 percent. Indoor humidity needs to be reduced below about 20F -- 5% for each 10 degrees F -- or condensation on windows and within walls can become a serious problem.
AFAIK, the highest efficiency forced air furnace available is 96%.
Be aware that most humidity guages are incredibly inaccurate -- often off by ten points or more.
happy?
There is an "ideal" range for health and comfort, from 30% relative humidity to 60%. Typically, the lower end is where you want to stay in the winter and the higher end for the summer, depending on the details of your home and location. I have a large home in the upper midwest where winters are very cold and dry (-17 was the lowest I saw this winter) so I have to add moisture to the air and try to keep it in the high 30's (% rh). I do this with a powered humidifer on the supply plenum of my furnace. In the summer, I get more humidity than high (100+) heat, so my intentionally undersized AC runs 20 hours/day at OAT over 95 and dehumidifies the air in the house well, keeping it in the 45 to 50% range most of the time.
If the air in your home is at 70 degrees F and 30% relative humidity, the dewpoint of that air is 54 degrees, at 70degF/50% rh, the dewpoint is 58. This will cause condesation on most windows in a cold environment. In your basement, unless the walls are very well insulated or you have a very well thought out ventilation system, the walls are cold approaching the dewpoint temp of the air and air is moved throught the space effectively. So you get a clammy, damp feel to the space.
>unless the walls are very well insulated or you have a very well thought out ventilation systemThat's a key qualification...you gotta know your walls and how they behave. One wall assembly can have different requirements from another based on how it allows temp and humidity to migrate...and require different equipment or controls.
Basements are problematic to treat properly. The typical, uninsulated or minimally insulated basement is one problem. Well insulated basements pose a different problem, that being that there is essentially no load due to outside air temperature, in either heating or cooling seasons. For most installations, air movement is somewhat, if not specifically, tied to the load; i.e sensible load in a space in btu/hr divided by 21.8 will give you the necessary cooling air flow. How to move air without over cooling or heating? There are a few options from which to select, but it has to be intentionally addressed by a competent professional.
I don't do basements. :)
Some might say that's all you do being surrounded by the concrete and all!My respects. Stu