Air Exchanger

[dnoz]

I am thinking about installing a air exchanger in my house. Does anybody know how difficult they are to install? Does anyone have a estimate on costs or recommendations of any installers in the north metro? Any information would be helpful.

[DRH1175]

How do you know if you need one? I know my Dad has one in his older home. I have a 1993 home and wonder if I should have one installed too. I have an insulated duct that runs from my outside to my cold air return.

[Wormdrowner]

If you have excessive condensation on your windows in the Winter, you would probably benefit from having an air exchanger. Another nice feature is your house will smell a lot fresher, it will get rid of smoke odors and cooking odors pretty quickly. If it's not new construction you might want to hire a qualified contractor to install. I installed ours before we sheetrocked...doing after the fact creates a lot more work. Back in 1992 ours cost around 1000.00 dollars. Call a few heating and cooling companies and get a few estimates. After having one I wouldn't be without it.

[bottomdweller]

I had one put in last year, 1300 dollars. I think it is well worth it.

[Down2Earth]

These things are just a big waste of money. We just built a new home and had to have one by code. The heating and plumbing guy said after one year everyone he knows turns them off. In the winter you pump in cold air and pump out the warm air. Opp. for the summer. The same guy also said you get enough air exchanged in your home by going in and out.

[Wildlineman]

I turn my air 2 air off in the Summer. In the winter it runs a lot and keeps the condensation off my windows. Works for me...

[harvey lee]

I would agree that it keeps all the condensation of my windows and opening the doors from going in and out does not help.

[BKB]

Never had one till we built our new house two years ago and I will never be without one now, we also shut it off in the summer.

[MNice]

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These things are just a big waste of money. We just built a new home and had to have one by code.

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FYI, these are NOT required by code, there are ways to build a new house without an air to air, but they are the easiest way to comply with the ventilation requirements.

[Down2Earth]

Any way you do it I assume it's wasting money. Allowing warm air out in the winter and cold air out in the summer. Mine hasn't ran in over a year now. The only time it wouldn't be a waste of money is the times of year you aren't running the furnace or the AC. I haven't even had condensation on any windows. If I did I'd just by a dehumidifier. Save the money and go on a hunting/fishing trip.

[Down2Earth]

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Another nice feature is your house will smell a lot fresher, it will get rid of smoke odors and cooking odors pretty quickly.

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It will make your house smell like the outside. So if the wind is right and you live next to an ethanol plant, sewage treatment center, a farm with animals on it, etc guess what your house will smell like.

[jerk bait]

You guys who turn off your air ex. in the winter are asking for trouble. Your house is a system with several working parts. The air exchanger is only one part but it is very important. It exchanges moist stale air for dryer fresh air. If it is installed correctly it will exchange the entire volume of air in your house once every 3 hours. If your house requires an air ex. by code it was built very tight. Imagine your entire house wrapped in plastic. The only way to get fresh air is from your air ex. Opening and closing doors can only let air in or out depending on the pressure in your house: Positive or Negative. Living in house that does not get fresh air exchange often enough can cause serious health problems. It can also damage your house even if you don't see condesation on your windows. You probably have moisture built up inside the walls or attic and aren't aware of it. This will lead to mold build up which can be serious. As for heating efficiancy is concerned, fresh dry air heats twice as efficiant as moist stale air. Think about it water is slower to heat and cool than air. Humid air has more water vapor. I could go on and on. If you want some more answers look on the UofM wabsite for cold climate housing.

[reddog]

(edit) Good post jerkbait. I didnt see page two when I wrote mine, so its a lttle redundant, and I agree with everything you said.

If you have a relatively new home and dont need any kind of mechanical ventilation, then your home is breathing on its own and not very energy efficient. If your home has a natural ventilation rate of 8-12 ach/hr, then you are correct, you wasted the money to install it, run it, and burn energy to replace the air it needlessly exchanges. In fact, its probably costing you considerably more to heat your home when you run it. BUT, if your home is breathing at a rate of 1.25 ach/hr @50 pa pressure (blower door diagnostics), then you darn well better have some way for that house to breathe, because this equates to a natural ventilation rate of about .35 ach/hr

Thermal efficiency in a home is half based on how well you do your thermal envelope and the other half is how air tight the envelope is.

More insulation doesn't make a home any more thermally efficient any more than more flour makes a better cake. Its just one part of a system in a house and one part of a recipe in a cake.

Moisture management within and through the structure is another key reason for mechanical ventilation. Not only are the occupants generating moisture and contaminants but, depending on how the house was put together, it could be taking on a large dose of moisture vapor from the ground also that needs to be exhausted out of the home. Relying on natural ventilation in an airtight structure wont work, unless you are going to open the doors and windows every hour or so and flush the house.

With a non airtight structure, relying on natural leakage points, like doors and windows, outlets, recessed lights, rim joists etc, can ventilate the house, but it is not controllable. Positive pressure(wind) on one side of the house, allows air to come in on that side, which is fine, but the negative side of the house is now exfiltrating, taking warm moist air along with it where it will condense on the first condensing surface, usually in the stud cavity, which is bad. The house breathes when the wind blows. Our forefathers homes were loose and drafty and ventilated on their own. They were also built before cavity insulation was popular, so they withstood the test of time, because they were able to dry, when they became wet. Not so with most of todays structures. When our homes of today become wet, they stay that way till a seasonal change allows it to dry.

Stack effect also plays a major part in ventilating a leaky structure. The larger the delta T (temperature differential) is, the more pressure is put on the upper levels of the home to exfiltrate, while the lower portions of the home are providing the makeup air for the stack effect. Hence a cold basement vs a warm upstairs. Heat can only rise, if allowed to rise. It has to be able to escape out the top and infiltrate at the bottom. The tighter the structure is, the less stratification of temperature between levels.

Central, mechanical ventilation, whether it is an HRV, ERV, or exhaust only is not a waste of money in a properly constructed energy efficient home. It is a necessity. 24/7/365

Retrofitting a new system into an existing home is not hard to do. Blower door testing, should be done first, to determine if the house is tight enought to justify mechanical ventilation, or, let the windows be your barometer. Even air tight, thermally efficient homes will carry moisture or even frost on the windows during periods of extremely cold weather. Its simple physics. There are two things you can do to eliminate moisture or frost on a window. Lower the rh of the home or warm the temperature of the glass to where is is no longer a condensing surface.

[hawgeye]

Down to Earth,

My guess is that you bought a cheap air exchanger. They make high efficiency ones now that are 95% efficient at bringing outside air to room temperature. They are definately not a waste of money. My brother's 5 year old house did not have an air exchanger. Long story short, he got mold on his windows and the $25,000 he had saved for a new boat went in to new windows. A house built right is built tight and if its tight you have to get the humidity and stale air out of your house.

Dave

[Down2Earth]

If it was cheap I'd hat to see an expensive one. Also with the new High Eff. Furnace they pull fresh air in from the outside. Mine is the high eff air exchanger but say it is 95% effective like you say. That is 5% longer both the furnace and the air cond. have to run. Which is a waste of money. The plumbing and heating person who put in everything has been in the business for over 15 years. Our house is built tighter then grandma's wallet. Still he told me he would only recommend running it for the first year or so and after that it was no longer needed but wouldn't hurt anything. He said the slab will be giving off moisture for the first year or so and that is why he recommended running it. Plus he said if I ever decided to get a indoor hot tub to start running it again.

[reddog]

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If it was cheap I'd hat to see an expensive one. Also with the new High Eff. Furnace they pull fresh air in from the outside. Mine is the high eff air exchanger but say it is 95% effective like you say. That is 5% longer both the furnace and the air cond. have to run. Which is a waste of money. The plumbing and heating person who put in everything has been in the business for over 15 years. Our house is built tighter then grandma's wallet. Still he told me he would only recommend running it for the first year or so and after that it was no longer needed but wouldn't hurt anything. He said the slab will be giving off moisture for the first year or so and that is why he recommended running it. Plus he said if I ever decided to get a indoor hot tub to start running it again.

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The air that the high efficiency furnace brings in, is combustion air. It never mixes with the house air. These are also sealed combustion units, because if they werent, they would be backdrafting into the house when they fired. All combustion appliances in a house, should be sealed combustion, including, the water heater, gas fireplace, etc.

I will agree that the first year drydown period is the most important regarding managing the moisture brought to the structure during construction in the concrete, lumber, drywall mud paint etc.

Like stated above, cold dry air is easier to reheat than warm moist stale air.

Its not physically possible to occupy a house 'tighter than grannies wallet" and not get excessive condensation on your windows during periods of cold weather. Whenever the glass gets cold enough to become the 1st condensing surface, moisture vapor turns back into water. I dont care if its on your windows, your cold water lines in the summer, or your beer bottle sitting on the counter. Moisture does not like being in a gaseous state. It wants to be a solid, whether thats water, or ice. It doesnt care.

Its hunting for a surface to condense on.

Maybe your home is extremely tight, but something, somewhere is causing it to breathe enough to cover your hind end when you shut your system off and whatever it is, is costing you money.

There are many potential air barrier bypasses that get overlooked every day in contruction, either because they dont know any better, or they just messed up. These bypasses can range from an open soffit above a kitchen cabinet or bathroom vanity that has connectivity to an interior wall and the attic space or lack of an air barrier in a fireplace chase. The opportunities are endless, and they all will ventilate your home, unknowingly.

As mentioned before, its a bad idea to shut these systems off. Typically, they are designed to run 24/7/365 on low speed to meet the requirements of residential housing.

When you shut them off, there usually is no "damper" system in them that closes, so now, they are subject to naturally ventilating your house thru positive and negative pressure, or stack effect, which ever is the stronger force on the system. Now, instead of one intake and one exhaust, you have two, with both feeding air into the home, or both exhausting, depending on which way the wind is blowing at the time, and where the exterior ports are located. When they are sitting idle, you lose the ability to exchange the heat molecules between the exhaust flow and the intake flow. Now, not only is it ventilating on its own, its also wasting energy on its own. Maybe this is why your home functions with it off?

Another reason for not turning them off is that condensation will form in the warm air side of the ductwork, when it mixes with the cold air coming in.

Go ahead and turn your off, if it works for you, but making a blanket statement that they are a waste of money is not the case. If your home functions fine with it off, theres a reason. If you're truly interested in saving energy, then I would find out what that reason is. Then, maybe you can turn your unit back on and let it do its job the way it was intended.

[jerk bait]

Reddog you beat me to it. You raise many good points. I can tell you are in the building industry as I am. This is what we teach our customers on a daily basis. The problem is that some have the same opinion as some on here. I guess this guy never changes oil in his car or drains the lower unit in his boat. The cost to fix your car or boat will be a fraction of what it will cost to fix your house in the future. Most problems with houses are not obvious. If you see a large amount of moisture on your windows that is only the tip of the iceberg. I would ask you to look in your attic in the winter. I would bet a weeks pay you will find frost on the underside of the roof decking. I also have a hard time beleiving a licensed HVAC/Plumbing contractor would make the statements you claim. I would get what he told you in writing so when, yes when, you have a problem you can take him to court rather than the general contractor. That is IF you used a licensed general contractor. Good luck with your home. I will do some simple math for you.

If you claim that your air ex. is wasting 5%[which it does not] but lets say it is. On an average sized home it costs between $1200 and $1500 in fuel to heat. %5 x 1200 = 60

%5 x 1500 = 75 I wouldn't take the chance on my health or the value of my home for so little.

[germanshorthairs]

down2earth, a humidifier uses electricity as well and I would bet that an air to air is more efficient than a dehumidifier.

[papabear]

the moisture problem is only one reason to use an air ex.

Indoor air quality is the main reason. the incidents of asthma and allergies has skyrocketed since the super tight houses became the norm. The reason is all the dust, mold, off gassing of chemicals and radon have no way to exit a house that is so tight. the one complete exchange of air every three hours is what it takes to maintain good air to breathe. The air ex. is meant to provide the fresh air that used to be provided by drafts in our homes. This winter open a door and notice which way the wind blows into or out of your house I bet it blows in if your air exchange is off.

[Down2Earth]

Ok now your getting rediculous. Why don't you just say something bad about my mom too. No I would never use a General Contractor but that's another topic. I'd just hire a Dang good carpenter who does all the generaling him/herself. By the way the wind is blowing really well today so I checked your theory and you are wrong.

Now I'm not saying you are wrong about the air exchanger because I'm for sure not the expert here. But I'm very good at math, in fact I'd go so far to say I know about as much math as anyone you could every hope to meet. So if a machine is 95% eff. that must mean it's 5% ineff. So I don't understand how you can say it isn't. It just makes your credit about the air exchanger look bad to me. But maybe you are right and just haven't explained it yet.

[Down2Earth]

I also think we are getting a little off track here. The person asked about installing an Air Exchanger. Which tells me when is house was built it wasn't required. Which in turn tells me his house wasn't built as tight. I could be wrong I don't know for a fact. But at the cost of an air exchanger (and someone losing a wage to install it, sell it, etc.) it would be cheaper to install a few ceiling fans, humidifier, or dehumidifier. Which ever is needed to solve the problem.

[reddog]

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I am thinking about installing a air exchanger in my house. Does anybody know how difficult they are to install? Does anyone have a estimate on costs or recommendations of any installers in the north metro? Any information would be helpful.

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I agree, we did venture off topic for a while. I apologize.

I dont have any answers as far as what a metro contractor would charge to retrofit a system into an existing home.

I do kno, that we have done many retrofits in existing homes, so it can be done. Most of the installs are exhaust only systems with make up supply air and run about 1K installed.

Now, there is no heat recovery with this system, but its fairly simple to install. It can go in the unconditioned space (attic) as long as it runs 24/7/365.

The system we usually retrofit with is an American Aldes VMPK 3 or 5 depending on the size of the house.

These systems take a 6inch 70 cfm duct out of the kitchen that is boostable to 140 cfm at a remote switch, usually near the kitchen to help with exhausting cooking odors.

The other ports are ran to each bathroom, and exhaust 20 cfm continuous, regardless of whether the fan is on high or low. Aldes uses an inline CAR (constant airflow regulator) to maintain 20cfm continuous. Its a small rubber baffle that expands when the duct pressure rises when the fan is kicked to high, therefore restricting the amount of volume exhausted at 20cfm.

There are also 10 cfm CARs, that are for like laundry rooms and larger family room applications where the potential for moisture and odors is minimized.

These systems are extremely simple to use and economical, because they dont cost an arm and a leg upfront, especially if you dont have one and need one.

Again, there is no heat recovery, they are exhaust only systems that are designed to run.

Fresh, makeup air is done with an inline duct to the cold air return of the furnace, and also has a CAR inline, to stop the furnace from pulling excessive amounts on air in.

The fresh air intake is usually adjustable, and there are times when it is not required, because the house leaks enough. Usually these home experience some kind of air quality issue, (usually excessive moisture for one reason or another)

Keeping the house under a slight negative pressure is better than a positive pressure in a heating climate. Positive pressure can force warm moist air into the wall cavity where it can do extreme damage in short order.

There are homes requiring 6 figure remodels that are less than 10 years old. (do a search on " imageevent defective home" and look at Lisas (Pa.) 7 year old home) While this was not a direct cause of interior moisture, interior moisture was an extenuating factor .

There are many homes that have been built over the last 20 years, that are tight enough to justify mechanical ventilation, but dont have it.

[dnoz]

My house was built in 1998 before Air Exchanger's became code. The way my current system is designed seems very inefficient. I have a vent on the outside of my house that is piped directly to my cold Air Return. I am getting fresh air but the furnace has to heat all of this cold air being pulled from outside. I had one furnace person tell me that when it is very cold I should disconnect that. I think I am going to go the Air Exchanger route I think it will pay for itself in the long run. I am going to call around for some estimates. If anybody has any recommendations for a installer in the north Metro let me know.

[reddog]

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My house was built in 1998 before Air Exchanger's became code. The way my current system is designed seems very inefficient. I have a vent on the outside of my house that is piped directly to my cold Air Return. I am getting fresh air but the furnace has to heat all of this cold air being pulled from outside. I had one furnace person tell me that when it is very cold I should disconnect that. I think I am going to go the Air Exchanger route I think it will pay for itself in the long run. I am going to call around for some estimates. If anybody has any recommendations for a installer in the north Metro let me know.

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You have a duct that comes from the outside and ties into the cold air return with no ability to restrict or control the flow into the furnace?

[KSW]

reddog

I just bought a new/used house that has a air exchanger. I'm not sure how to set it on the control. Do I change it as the outside temp goes down?