I started trying to get estimates today, and with one company I contacted for an estimate on a Santa Fe Compact dehumidifier and an Aprilaire 600 humidifier, the owner told me that it sounds like the problem we have is not going to be fixed by a humidifier and dehumidifier. He said that we could very well end up spending money on the dehumidifier and humidifier, and then having them run up the electric bill, and still not getting to our desired humidity levels because our air leakage is high (it was 3667 at the first home energy audit, then insulation and air sealing brought it down to 3150 or so). He said that we should be trying to get the air tightness down to 2500 CFM50, and that he's done that for people, but it would cost a whole heckuva lot of money, a lot more than getting a dehumidifier and a humidifier, and actually even more than we spent on getting a totally new furnace and AC system. He said that we should also be taking a look at the duct system, which the home energy audit showed to be not performing efficiently. A ComfortMaxx Quick Check Customer Report of the cooling system a year ago showed that the duct system operating efficiency was 50%. He said that the amount of reduction in CFM50 is not enough, you can go down 500 just by insulating the attic hatch. He said it shouldn't be the case that the house quickly (in the space of hours) goes back up to 65% humidity after a normal cooling load brings it down to 50%, that means that we need more air sealing.
So now I'm stuck between a rock and a hard place. If he's right, a new humidifier and dehumidifier wouldn't solve the issue, the only thing that would solve it is spending much, much more money on air sealing and increasing duct efficiency. And I haven't got a big enough budget for that, sadly.
And my neighbor, who's an architect of some sort, tells me that the problem is that I need to get an exhaust fan over the gas stove in the kitchen. So lots of different theories about how to fix the humidity problem.
How much cooking do you do? What are the different components that your walls are composed of? That room over the garage is probably very well connected to the garage.Air wise.
An answer without a question is meaningless.
Information without understanding is useless.
You can lead a horse to water............
You don't know me from a bale of hay. I can assure that there is enough moisture left on your a/c coil at the end of the cooling cycle that evaporates back into your home and raises the indoor %RH 10% within on hour. It has nothing to do with air leakage. Its the moisture on your a/c coil/pan and you breathing. It has to do with your a/c not running enough to remove the moisture from you and a small amount of high dew point infiltrating your home. You need to remove a 1-4 lbs. of moisture from your home per hour to maintain <50%RH, depending on the outdoor dew point, the amount of infiltration, and the number of occupants in your home.
Originally Posted by Dr Gaius Baltar
If you want to know for sure how much fresh air is actually infiltrating your home, get a CO2 meter and monitor the CO2 levels. I can help you with this. There $100 at CO2.com During mild, calm weather, minimal fresh air gets into your home. When your a/c operates a significant amount, your %RH is <50%,Right?
Properly ventilated homes need supplemental dehumidification when the outdoor dew point is above 60^F and low/no cooling loads. These are engineering principles that many a/c techs do not comprehend.
You need 100 cfm fresh air in most homes to purge indoor pollutants and renew oxygen, winter or summer when the home is occupied.
Two occupants provide 1 lbs. of moisture per hour. You need 2-3 lbs. of moisture per hour to humidify during low winter outdoor dew points.
If you want the ideal comfort, you need a humidifier during extreme cold weather and a 2-4 lbs. per hour dehumidification during the summer.
The rest is up to you.
Yes tightening your home up less the need for winter humidification and summer dehumidification.
Extreme air tightening is unhealthy but cuts down on problem.
Good Luck. Keep us posted.
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"
An exhaust fan over the stove, would then require fresh air to be pulled into the house to make up for the air you exhausted. So you would still have high humidity.
Originally Posted by Dr Gaius Baltar
Lately, I do about 1 hour of cooking per day. The foundation walls are masonry, exterior walls are siding. Interior walls are drywall.
Teddy bear, when the a/c operates a significant amount, RH is about 50%. The owner of the business that I was contacting for a quote on a Santa Fe Compact dehumidifier and Aprilaire 600 humidifier believed that homes are supposed to always have humidity levels of around 50% without a dehumidifier or humidifier. So if that's not true, then I guess that casts doubt on the other things he was suggesting.
beenthere, Oh. D'oh!
Here's a basic view of what happens to a house, concerning humidity levels, as you make it more airtight:
- In winter, a tight house seldom needs humidity added. It will need controlled ventilation to keep humidity levels from rising too high, and to assure the indoor air does not become foul.
- In summer, a tight house will need fresh air and dehumidification to control mainly indoor sources of moisture generation; i.e. cooking, showering, etc. Overall it will be much easier to dehumidify than a leaky house (because humidity is not seeping in uncontrolled through gaps and cracks everywhere), and the a/c can normally accomplish the job without a supplemental dehumidifier
- In spring and fall, a tight house still needs fresh air. Depending on how humid the air is outside, a dehumidifier may be required...at other times just fresh air can meet the need.
That said, what Teddy Bear said about moisture on the cooling coil re-evaporating back into the house applies mainly if the indoor blower is left running when the compressor outdoors has cycled off...which we have already discussed on this thread is not advisable in humid climates. What I would like clarity from you on is if you see notable spikes in your indoor humidity levels when the compressor AND indoor blower cycle off. This means you would need to ensure the blower does not run even on the very low speed it does when in circulation mode. If humidity spikes with the a/c completely off (including indoor blower) then you have some serious air leakage issues with your house. A slow rise would be expected, but not a sudden one.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
Okay, I am setting the AC to 65 and taking 1-hour snapshots of the humidity level at the main air return near the thermostat on the main level (not the basement). Once the humidistat gets down as low as it will go humidity-wise, I'll set the AC back to a normal setting, and see what the humidity is at again in 1-hour increments. Fan on AUTO.
08-01-2013, 06:33 PM
1:00PM: Starting the experiment. Set fan to AUTO. Reduce thermostat from 73 to 65. Humidistat reads 61%, 73F.
2:00PM: Humidistat reads 54%, 72F.
2:30PM: Humidistat reads 52%, 72F.
3:00PM: Humidistat reads 51%, 70F. It seems to me that humidity has gone as far down as it will go (it's less than 85F outside, so I don't think the AC will go into stage 2). I reset the thermostat back to 73F. Fan remains on AUTO.
3:30PM: Humidistat reads 53%, 72F.
4:00PM: Humidistat reads 52%, 73F.
5:00PM: Humidistat reads 53%, 73F.
6:00PM: Humidistat reads 55%, 73F.
6:30PM: Humidistat reads 55%, 75F.
During this time, no cooking on the gas stove (a little bit in a toaster oven), no showering.
After I reset the thermostat to 73F, the AC didn't turn on again all that much. Maybe once for 5 minutes or so.
08-01-2013, 08:01 PM
So from 3 PM till 6:30 PM, your homes total(grains of moisture per pound of air) moisture content increase by 22%. or an average of 6.28% per hour.
08-01-2013, 08:20 PM
What does that say about my home? Am I gaining humidity at an accelerated pace? Or is this normal? Should that change my mind about whether to get a dehumidifier and humidifier?
7:00PM: Humidistat reads 56%, 73F.
8:00PM: Humidistat reads 56%, 73F.
08-01-2013, 08:57 PM
Dehumidifier. Don't know that you will need a humidifier.
08-01-2013, 09:34 PM
Yes, I think I would look into a dehumidifier.
There are things one can do to 'tighten' a house (caulking, insulation, those gaskets behind switches and outlets, foam sealing all the penetrations both inside and out-- like water faucets outside and water/drain penetrations inside). Your example did not include cooking or showering... which is a significant amount of humidity added indoors.
I think the whole house de-humidifier would be a good investment. Note it usually has its own separate air filter, I would watch that filter carefully for a few mos until I understood the change times.
A humidifier (which adds humidity) is for the winter when it is cold outside and the house gets dried out due to forced air heat. I would wait until the dead of winter to see if you really need it. Humidifiers are a bit less complicated to install than de-humidifiers.
Let us know how it works out.
When your home is comfortable, Six will probably come back to visit... <grin>
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