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  1. #1
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    Default Nutone Air-to-Air Heat Exchanger

    I saw this in a 40 yeard old house yesterday. The manufacturer label says it is an air-to-air heat exchanger. It had separate intake and outtake vent hoods on the exterior side wall of the house. Two supply ducts branching off of it into the finished areas of the basement. When I turned it on, the round wheel of plastic-type strips (see in pic 2) rotated and the fan blower kicked on but it produced no heat or temperature change. I alreday called it out for being a potential problem being located too close to the oil-fired boiler.

    Does anybody have any familiaruty with this unit? It has no coils and no refrigerant lines. It seems any heat it is supposed to generate starts with the rotating wheel of platsic strips.

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  2. #2
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Arrrgh! Pics here.

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    Jerry Peck's Avatar
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Nick,

    Where did that duct go?

    "air-to-air heat exchanger" makes me think of an outdoor fresh air make up where heat from inside is used to warm cold air entering from outdoors, so the fresh air make up air is closer to return air temperature.

    Does that make sense, or did I just babble on?

    It's not a "heater", but a "heat exchanger".

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  4. #4
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    Default Re: Nutone Air-to-Air Heat Exchanger

    That looks like a commercial air handler. I have seen units that look like in buildings above a suspended ceiling.

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  5. #5
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    Default Re: Nutone Air-to-Air Heat Exchanger

    So are these units supposed to actually generate some type of heat? This one did nothing but blow air.

    Jerry, the duct you see in the pic is a supply duct blowing into one of the finished rooms in the basement. What my pics do not show are the fresh are intake and exhaust lines. There were two separate vent hoods on the side exterior wall for the intake and outtake.


  6. #6
    John Arnold's Avatar
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Nick - If the temp inside and outside are close to the same, you wouldn't notice any heating or cooling taking place, if I understand these things.
    Let's say the house is very tight and it's winter. The heat exchanger brings in cold fresh air, but heats it with heat extracted from the warm but non-fresh indoor air that its sending outside. Hence, the "exchange". I've never seen one, but I've heard about them.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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    Default Re: Nutone Air-to-Air Heat Exchanger

    I think it is just exchanging air from outside with the air inside. The concept is to blow the incoming air past the outgoing air, to help warm it up before it hits the inside of the house. We will see more in the next 20 years as fuel costs rise and houses get even tighter than they are now. It won't generate heat, per se, but it should raise the incoming air temperature (or lower, depending on what time of year) from the outside. The proximity to the boiler, etc. shouldn't be relevant if it is pulling air from the outside and everything is sealed up properly.

    Jim Robinson
    New Mexico, USA

  8. #8
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    Default Re: Nutone Air-to-Air Heat Exchanger

    I guess I'm getting a little confused here in terms of how much heat this type of unit can generate. It sounds like it's primary function is to introduce fresh outside air to the interior air with heat generation being secondary. Assuming an exterior temperature of 40 degrees and an interior ambient air temperature of 68 degrees, is one of these units when functioning properly enough to serve as the primary heat source for a finished basement (size of unit and size of space considered)?


  9. #9
    Thom Walker's Avatar
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Would this look like a modern version of your setup?
    http://www.broan.com/display/router.asp?ProductID=2187

    I think this article explains improvements to what you were looking at.
    http://www.patentstorm.us/patents/6176305-claims.html

    I suspect that it was used for dehumidification as much as for heat.


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    Default Re: Nutone Air-to-Air Heat Exchanger

    Also acts a as whole house air filter, you sometimes see them installed ahead of a electrostatic filter - in this case the ES filter can go years without cleaning.

    I have one of these in my house, works quite well:

    UltimateAir RecoupAerator®::Learn More!


  11. #11
    Bob Mayer's Avatar
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Quote Originally Posted by Nick Ostrowski View Post
    I guess I'm getting a little confused here in terms of how much heat this type of unit can generate. It sounds like it's primary function is to introduce fresh outside air to the interior air with heat generation being secondary. Assuming an exterior temperature of 40 degrees and an interior ambient air temperature of 68 degrees, is one of these units when functioning properly enough to serve as the primary heat source for a finished basement (size of unit and size of space considered)?
    Air-to-air heat exchangers do not generate heat, they conserve or transfer it. Do not think of heat generation when considering these units.

    Residential air-to-air heat exchangers, also known as heat-recovery ventilators, are used to provide fresh air while minimizing heat loss, or in cooling season, heat gain. The heat exchanger in a gas-fired furnace is (duh) an air-to-air heat exchanger. Heat is moved from the warmer air stream to the cooler one without the movement of any of the physical portion of the stream from one side to the other.

    Houses require air exchange with the exterior to avoid the buildup of noxious substances, including, perhaps, moisture, in the air inside the house, a general recommendation is for 1/3 of an air exchange per hour. There are two different ways of doing this, which, for simplification and objectivity , I will label The Good Way and The Bad Way.

    I will discuss this in terms of the heat flow during the heating season. In The Bad Way, a house, by design or not, is built with a certain amount of leakage. Driven by the stack effect and wind pressure, cold air flows into the house and warm air flows out. The rate of air exchange increases with decreasing temperature and increasing wind speed. The air exchange rate is not controlable by the occupant for different conditions inside the home (except for opening windows) to adjust for internal contamination conditions, such as cooking or have many guests. Instead, the air exchange rate increase with greater inside-outside temperature differential, meaning that the heat loss increases exponentially with increasing temperature differential, because each unit of air causes more heat loss because of the greater temperature differential and there is more air being lost because of the increase of the forcing of the stack effect. The air transfer movement is determined by where the leaks are. Some parts of the house may have too much ventilation, some too little. This system provides random air exchange with maximal heat loss.

    In The Good Way, the house is build as tightly as possible, so that there is almost no air exchange. A whole-house heat recovery ventilation system is installed, with air being brought into the 'clean' rooms, such as bedrooms, and the living room, and exhausted from the 'dirty' rooms, such as bathrooms and the kitchen. The system is designed for no dead spots and the longest possible path between incoming air vents and the exhaust vents. In the heat exchanger itself, outgoing stale air warms the incoming clean air, with about a 75% conversion efficiency. Most systems have two or more fan speeds, for more air exchange when conditions warrent. The system's air exchange rate is effectively independent of outside weather conditions. The system provides the maximum benefits of air exchange with minimal heat loss.

    One of the benefits of a heat recovery ventilation system is that is minimizes indoor-outdoor pressure differences. I installed such a system in my house when it was built in 1994. We measured indoor-outdoor pressure differences under four conditions, with the system on and off, and with the exhaust fans (kitchen and the half bath too remote to put into the system) on and off. There was less pressure differential with the system and the exhaust fans on than with neither on. The system, in addition to its other benefits, provides pressure balancing.

    The system Nick has shown is a wheel system. Wheel systems generally are used where there is the desire to move water vapor, as well as heat, across the streams. Such systems may have a small amount of cross-contamination. See, for example, Building Performance Equipment, Inc. - Air to Air Heat Exchangers.

    I have a background in thermodynamics, and I cannot imagine building a house without a heat-recovery ventilator. My system is from American ALDES American Aldes Ventilation Corporation. But I am opinionated, I would not have a scorched-forced-air system either.

    If you choose to evaluate such a system, check for airflow at the intake and exhaust vents in the house. If it is very cold, or hot, outside, the incoming air should be closer in temperature to the inside air than to the outside air. Most incoming vents will be at about 20 cfm, if the only ventilation in a bathroom, the exhaust vent must be at least 20 cfm, the kitchen exhaust flow will be much higher, it probably provides most of the exhaust for the house.

    - BOB


  12. #12
    Lowell Dahlman's Avatar
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    Default Re: Nutone Air-to-Air Heat Exchanger

    Bob is correct in his assessments regarding home air exchange and that the unit you are looking at is not a matter of heating or being a heating element in and of itself. It is helping to recover the heat that you already have in your home and not waste the energy on heating the air outdoors.

    Hoyme Manufacturing makes a motorless heat exchanger that uses the fan of your furnace (or any other in-line fan for that matter) to service the air through and exchange the stale air indoors with fresh air from outside in a controlled manner. In this way your are not losing the energy cost of having the warm air inside be lost to the cold air outside without first warming up the fresh air you need in your home. Energy cost are way too high to pay to heat the outdoors as well as your home. Hence the Heat recovery(or cool air recovery if you are in a warmer climate).
    I post this here because there is a diagram on the Hoyme website that may be useful in showing how this works.

    Hoyme Manufacturing Inc - Motorized Dampers & Ventilators - North America

    There is more information on Air Exchangers here.

    Hoyme Manufacturing Inc - Motorized Dampers & Ventilators - North America

    Nice thing being that the Hoyme Air exchanger is also not prone to frosting issues which has a negative impact on the effectiveness of the some of the other air exchangers on the market. And being motorless and using the furnace fan there is no risk of the air exchanger being a fire hazard as has been the case for some other air exchangers when their internal fan motor burns out or over heats.

    Again I offer this just as helpful information.

    Lowell


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