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BoxMN

Air exchanger questions

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First time with air exchanger. New construction, and there is a bit of condensation on bottom of windows. Our contractor saw this and said he turned up the rate to 30% to help get rid of moisture, as he says that new places have moisture still in the wood, etc, and then after it starts to dry out that you turn it back down. I was just wondering if more moisture just put into the house via the air exchanger during snowfall, etc?...

And if you all agree with turning the air exchangewr a bit higher to help get rid of mositure, as some poeple recommend to me to turn it off iin the winter...

Thanks for advice and thoughts!

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In winter theres not as much moisture (Humidity)in the air,That lumber dryin statement seems wierd! your interior is sealed with plastic vaperbarrior = no moisture entering through the walls & lumber.The fresh air drawn in from exchanger or required outside air to mix is probably the moisture issue.

What to do? I have no experience with exchangers,However when the fresh air from outside is the 6,8,10 inch flex and moisture build up was detected I just closed it off,I figured no need to heat COLD air and have moisture problems,just going in & out supplied fresh air!

Another regulation that is in my opinion foolish! (Making houses air tight extremely air tight!)

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I kinda thought that as well, but there is a lot of pine in the house - trim, doors, ceiling, and some basement framing - not sure if enough to have noticable moisture. But he said it is normal and expected. My wife did a bunch of cooking, so maybe that helped add to it, and I certaily have been going in and out plenty smile

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Thats all kiln dried lumber,once installed it may pick up more moisture,but its so low in moisture thats not it.Its probably finished also sealed from moisture.

Kinda like wood floors you have to leave expansion room for when moisture enters the wood cause its kiln dried and has real low moisture content.

To sum it up I dont belive what was said about moisture comming out of the finish wood or any wood.

The cooking adds yes,

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Last year was our 1st year with an air exchanger. It took a couple weeks of tinkering before we found the right setting. Make small adjustments, I started out going from condensation on windows to getting static shocks a few times by changing it to much. Talking to other people that have them it seems every house has its own "sweet spot" setting and trial and error is the only way to find it.

I know when there is alot of cooking going on the stove top it seems to increase the moisture in the house quite a bit.

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Actually, my experience is new build moisture mostly comes out of the concrete in the basement. I know when my Uncle built a new home, he had moisture problems for 3-4 years until the slab and other concrete in the basement dried out.

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You know Jolly, I didn't remember that until now, but he did say the moisture in the slab. For some reason I remember "wood" but now that you mention it, it was the slab he was talking about... so much new stuff for me, I am learning a lot, but I am not exactly the brightest bulb on the tree...

"Sparce", yep, all wood is finished, and all sealed, so I uinderstand what you are saying it not being from the wood.

Thanks guys, I guess some fine tuning and finding the spot, and letting slab time to slough off moisture....

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2 kinds of air exchangers HRV Heat recovery ventilator and ERV Energy recovery ventilator They are both great they basically take the place of fart fans and unitentional air infiltration (leaky walls) They are touchy you will have to toy with the humidistat to get it set to your liking. as long as you don't have water running down your windows your home will feel more comfy with a higher humidity. Also there is lots and lots of water induced during construction in my opinion the biggest culprit is sheetrock and sheetrock mud they mix alot of water in there. paint has high moisture so does stain as well as carpet glue and grout. Any thing that needs to dry put some moisture in the house you will have to adjust accordingly.

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Actually, the relative humidity in the winter time, often exceeds the summer relative humidity. The difference is... air temperature. Lets say that 10 cu ft of air at 90 degrees can hold 2 oz of water. (Lets say 82%- these numbers are for illustrative purposes only )The warmer the air, the more capacity it has to carry water vapor. Mpls. Mn, on a -25 degree day, still averages 82%RH, Mpls. Mn. on a 95 degree day, averages 82% relative humidity

Now, in the winter time, you can take the same amount of air 10 cu ft, at 0 degrees, and it still carries 2 oz of water vapor. again, 82% rh.

Cold air is compressed air, it expands when heated.

What happens when you bring in cold moist air from the outside is that when you bring it in and warmed to room temps the volume of air explodes/expands but the actual amount of moisture vapor remains static. So now, your 10 cu ft of air at 0 degrees, turns into 80 cu ft of air at 70 degrees inside your home, but the moisture volume stays the same, so the Rh is now about 10% for the original ten cubic feet of air you brought into the home, That is how winter air dehumidifies a home in the winter. There is no way to get rid of excess moisture in the winter time without bringing in fresh air, or increasing the temp, which allows the air to carry more RH.

Now, we get into stack/chimnney effect on a house. When that air expands, it pressurizes the house and the pressure is equalized by the balancing effect of the fan.

Non airtight homes that breathe on their own, have the same thing happen to them, although, since they are not airtight, the warm air rises and excapes out the top of the house thru the ceiling cans, interior walls, interior soffits that are not sealed off to the attic space. etc. When stack effect takes over a home, the warm air rises and excapes, while cooler air is being pulled in my infiltration on the lower levels. Hence a cold basement and a too warm upper level. Stratification, its called. An airtight house, restricts stratification, because the air cannot leak out the top or leak in at the bottom. Think about a hot air balloon, The only reason it can float, is because the hot air is restricted from exiting out the top, the only way it can come down, is to open the top slowly and allow the hot bouyant air to excape and let the balloon drop. Its exactly the same with a house, only on a lot larger scale.

Building an airtight home is a great and necessary thing. What you are in effect doing is eliminating the wind from ventilating your home for you, which is uncontrollable.

Yes, a house has to breathe, no doubt about it, but by using mechanical ventilation on an airtight home you are in effect putting the home on a ventilator that you have control of, which is again, a good thing.

As far as condensation on the windows, during extreme temps, you are just going to have to expect some condensation around the edges. There are only two ways to avoid it. Over ventilate the house, which will cause static electricity and dry noses, or warm the surface of the glass by moving air across it.

As stated here before, you will need to monkey around with the settings to come up with a "sweet spot" for your home.

And, as also stated, the first year is usually the worst, with concrete, drywall, paint, and everything else acclimating itself to the level of RH that you want in your home. Where the sweet spot is this year, will probably not be where it will be next year, or possibly the year after, if the winters are different.

Run the ventilator, and forget about it, with the excption of servicing it annually.

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I was told that also about the wood (we have a lot of wood floors) that over the course of the year will tend to absorb moisture and this will cause condensation on the windows early in the winter. I had the same problem one year and I asked an HVAC guy about it and the first question he had was, "Do you have wood floors?" He also stated that once you turn on your air conditioner in the summer, shut off the air exchange until you are done with the AC in the fall.

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Actually, my experience is new build moisture mostly comes out of the concrete in the basement. I know when my Uncle built a new home, he had moisture problems for 3-4 years until the slab and other concrete in the basement dried out.

Jolly yer one smart feller.

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You know Jolly, I didn't remember that until now, but he did say the moisture in the slab. For some reason I remember "wood" but now that you mention it, it was the slab he was talking about... so much new stuff for me, I am learning a lot, but I am not exactly the brightest bulb on the tree...

Shack, yep, all wood is finished, and all sealed, so I uinderstand what you are saying it not being from the wood.

Thanks guys, I guess some fine tuning and finding the spot, and letting slab time to slough off moisture....

Box thats the second post you called me shack?thats ok Shacks allright.

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Sparcebag, sorry man! I told you I am not the brightest bulb on the tree! But I do know the difference - Shack is garage dude and Sparce is cabin dude wink

Sorry man, I owe you a couple brews if we ever meet smile

edit - drat, I even spelled sparce wrong on the first try... I need to go back to school...

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No problem! Thanks but I dont Drink,too much partyin when I was younger bein stupid. But Steak & lobster will do. grin

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