relative humidity

[jlore]

how do you measure relative humidity? it seems when i run to stove for a couple days i start to get sinus headaches. does that happen to anyone else or is just in my mind?

 

[jadm]

The therm. I got measures temp. and humidity. Got it at Ace Hardware.

 

[jdurando]

Humidity is measured with a Hygrometer some thermostats also have a Hygrometer built in or you can get one at any hardware or big box store. A lot of them come with thermometers too

 

[FLINT]

a hygrometer measures humidity. you can get them either by themselves or as a combo with a thermometer. should be able to get one almost anywhere - any hardware store or even walmart. I just bought one for $4 at i think walmart.

 

[Corey]

I don't get headaches or anything, but the indoor air can get pretty dry in the winter, so some type of vaporizer may be in order.

 

[pen]

Above 20 degrees I keep things at 45% humidity with a humidifier and a steamer on the stove.

Below 20 degrees I keep things at 40% If I go above those numbers my windows will collect moisture at the bottom and below these the wife gets noseblled.

I have not had good luck with this type of digital hygrometer. Other digital ones I have used (the cheaper non-research grade) have also been unreliable for me.

Here is the one I do not like that I own. It works very accurately for temp but the R.Humidity is way off

This is the hygrometer that I use and trust. No electronic interpretation, this is the real deal.

mine is similar to this with the only difference being a rotating cylinder in the center that is used to do the dry bulb vs wet bulb conversion to calculate RH.

 

[Martin Strand III]

Above 20 degrees I keep things at 45% humidity with a humidifier and a steamer on the stove.

Below 20 degrees I keep things at 40% If I go above those numbers my windows will collect moisture at the bottom and below these the wife gets noseblled.

I have not had good luck with this type of digital hygrometer. Other digital ones I have used (the cheaper non-research grade) have also been unreliable for me.

Here is the one I do not like that I own. It works very accurately for temp but the R.Humidity is way off

This is the hygrometer that I use and trust. No electronic interpretation, this is the real deal.

mine is similar to this with the only difference being a rotating cylinder in the center that is used to do the dry bulb vs wet bulb conversion to calculate RH.

Maybe it's me but the Taylor model (non-electrical, no batteries, the "real deal") has identical *F temperature scales to "130" on both sides and the readings are identical at "80". Curious, eah? I thought a humidity reading could only max at "100".

Anyone else see this?

Aye,
Marty

 

[jlore]

cool, thanks for the replies

 

[oconnor]

Maybe it's me but the Taylor model (non-electrical, no batteries, the "real deal") has identical *F temperature scales to "130" on both sides and the readings are identical at "80". Curious, eah? I thought a humidity reading could only max at "100".

Anyone else see this?

Aye,
Marty

The unit displays wet bulb and dry bulb temp. The difference is used in a table to calulate RH.

 

[SteveT]

Circuit City has a sale this week on an indoor/outdoor thermometer with an indoor RH indicator.

(broken link removed)

I have a different model (same manufacturer) and as far as I can tell both the temperature and RH are very accurate.

 

[pen]

Above 20 degrees I keep things at 45% humidity with a humidifier and a steamer on the stove.

Below 20 degrees I keep things at 40% If I go above those numbers my windows will collect moisture at the bottom and below these the wife gets noseblled.

I have not had good luck with this type of digital hygrometer. Other digital ones I have used (the cheaper non-research grade) have also been unreliable for me.

Here is the one I do not like that I own. It works very accurately for temp but the R.Humidity is way off



This is the hygrometer that I use and trust. No electronic interpretation, this is the real deal.

mine is similar to this with the only difference being a rotating cylinder in the center that is used to do the dry bulb vs wet bulb conversion to calculate RH.



Maybe it's me but the Taylor model (non-electrical, no batteries, the "real deal") has identical *F temperature scales to "130" on both sides and the readings are identical at "80". Curious, eah? I thought a humidity reading could only max at "100".

Anyone else see this?

Aye,
Marty

Marty, that is a picture from a site selling those. There is no water in the bulb so it wouldn't be reading different. Thats not mine in use.

pen

 

[WarmGuy]

I have the ACU-RITE model above and it has worked very well for me. I calibrated it (google for info) and found that it was off by 3%. So I just add 3% to the reading and I'm pretty confident in it. It's good enough for my purposes.

Here's my question: how does a wood stove decrease the RH, apart from heating the air?

 

[Slow1]

Here's my question: how does a wood stove decrease the RH, apart from heating the air?

Relatively speaking, that's it

Seriously - stove doesn't actually remove a significant amount of water from the air (although one can argue that since some air is removed from the room for combustion and that may have more moisture than the air being pulled in from outside to replace it that in fact SOME water is removed from the house I think if one were to do the calculation you would find this to be insignificant in the big picture). However, it does warm the air and since warmer air can hold more water, the relative aspect of "relative" humidity comes into play - the amount of water in the air remains constant, temperature goes up, thus the percentage of capacity that the air can hold that is used is now less.

One way to think of it is like a bucket with water. The bucket is the air's ability to hold the water. As it gets warmer the bucket gets larger, as it gets colder it gets smaller. Unless you put water in or out, the amount of water stays the same. If the bucket is half full then you are at 50% relative humidity. You double the size of the bucket (heat the air enough to double it's capacity), then the bucket will be 25% full (same amount of water). If had halved the bucket (cooled it) then it would be 100% full - go and smaller and the water leaks (condensation - fog or rain if it is actual humidity).

 

[pen]

I have the ACU-RITE model above and it has worked very well for me. I calibrated it (google for info) and found that it was off by 3%. So I just add 3% to the reading and I'm pretty confident in it. It's good enough for my purposes.

Here's my question: how does a wood stove decrease the RH, apart from heating the air?

wood stoves don't necessarily dry out the air as much as thier combustion doesn't add moisture to the air.

Non vented propane wall heaters will add a lot of moisture to the air as their byproducts of combustion (CO2 and H20) are allowed to stay in the room.

With a wood stove, propane furnace, oil furnace, or any combustion style system that vents outside, the moisture produces during combustion leaves.

However, due to wood stoves being less effecient than other combustion furnaces, they require more air (oxygen) since to get the same BTU's into the room since so many go up the chimney.

Cold outside air contains very little moisture as cold air molecules are unable to hold on to much water vapor. Because of this, the air that your stove draws into the home is "relatively" dry and as it warms up, the previous cold air now can hold more water vapor and thus the RH drops.

It's easier if you look it up on google and find an example.

pen

 

[oconnor]

Second to Slow1's excellent explanation, is that once you heat the air inside the house, increased air leakage can occur, especially in an older two story, or when windows leak etc. Increaseing the temp in the house can increase the air change rate, and the air outside is much drier (actually drier, even though the RH may show it as wetter) than inside air. This is what kept my house at sub 20% RH all last year.

Sealed the windows and basement sill plate, and now, less airchange, and better humidity control.

Old non EPA stoves and open fireplaces are horrible as far as airchange issues go as they pump huge amounts of air out of the house. Newer EPA stoves actually vent less home air than most bath fans (I've read 40-90 CFM for EPA stoves), hence bath fans can reverse chimney flow in less than ideal setups.

Edit - If you add an OAK, then the stove isn't venting any inside air from the home.

See "Keeping The Heat In" at this link - http://oee.nrcan.gc.ca/keep_heat_in/introduction.cfm - to get an idea of how air leakage affects lots of issues in the house.

 

[Highbeam]

Having a stove pull combustion air doesn't prevent the RH from going down in the cold months. I am plumbed to OAK and still have low RH. It would be dier IMO if I was sucking the inside air into the stove to burn since it would be replaced by 20 degree air at 16% RH right now and by using Slow's example that would be a small bucket with a tiny amount of water in it.

Outside air, once heated to inside temps, will be much drier than the inside air so every time you open the door or get outside air into your home (corresponding leakage of inside air leaks out) then you will be lowering RH.

Woodstoves don't dry the air. The air is already dry.

 

[oconnor]

I think in the end, the best way to raise the RH, other than boiling water, or storing 4 cord of green wood in the basement, is to keep as much of the outside air from entering the house as is reasonable, and to do that we need to keep as much of the inside air from leaving as is reasonable.

Jlore, you mention headaches - I get the same, but it's worse if I get a face full of smoke. Do you get any smoke spillage when you load?