Over the years, many promising inventions (and “improvements”) have adorned HVAC equipment.  Not all of them proved to be of great value.  Some even turned out to be problematic, and remain in place on systems we encounter.  The same applies to a few furnace and A/C unit designs too.  Trial and error is a basic part of the design process.  That’s how “better mousetraps” come about.  In any large industry, people all have different likes and dislikes.  Mine are quite similar to those of most of my experienced colleagues.  We’ve all been fooled by smoke and mirrors marketing at least once or learned over time that certain designs just didn’t work as well as expected or created undesired side effects.


Olden day devices


  1. A white plastic box a local electric company installed on (or near) your outside A/C unit with the homeowner’s consent many years ago, in order to “reduce their peak demand”.  In return for allowing this to be installed on their systems, the homeowner received a $10 a month discount for 3 months during the A/C season.  The box contained a thermostat and a timer mechanism, and it would cycle the outside system off for 5 minutes every half hour after the outdoor temperature reached a certain number of degrees.  This would cause many systems not to be able to keep up on warmer days.  It also caused them to use more electricity, because it didn’t cycle off the indoor blower system during the off cycle.  The program was discontinued several years ago, but many of the boxes are still installed.  The electric company doesn’t want the boxes back.  And they need to be disconnected if they are still there.  The electric company will not send people out to remove them.  (The electric companies are now using a different strategy to control, i.e. minimize peak demand by installing radio controlled thermostats in customer’s homes.  This method gives them more control over the peak demand than the old plastic box did.) 
  2. After-market “energy saving” boxes installed on or near the furnace that were supposed to save you money on your gas bills by periodically cycling the electric valve in the furnace that delivers the gas to the burners.  The savings never seemed to materialize and it could also cause acidic condensation issues and poor drafting issues.  These also need to be removed or at least electrically disconnected.  (As an amusing asides, I once ran a call where a gas company technician had shut off and “red-tagged” the furnace because it was “short-cycling”.  The short-cycling was actually the device doing what it was designed to do – cycle the burners on and off.)
  3. After-market thermal flue dampers.  These were typically cylindrically shaped stainless steel housed devices installed in the galvanized flue systems of furnaces and some water heaters.  These devices had metal “fingers” in them that were supposed to close off the flue system when the furnace wasn’t running.  When the furnace came on, the heat would cause the fingers to “automatically” open to allow the flue gases to travel through and go up the flue pipe.  The problem was that the fingers would bind/stick in the closed position and not allow the flue gases to exit.  These devices should either be removed and replaced with galvanized flue pipe, or the guts should be ripped out of them, leaving only the stainless steel housing.  NOTE: These are NOT the ones with the electric motor boxes on the side.  Those are MOTOR OPERATED – not THERMAL flue dampers.
  4. After-market electronic pilot re-lighters.  These were just a bad idea.  They’re somewhat similar to the “trick birthday candles” you can’t blow out.  As soon as the pilot is extinguished, the automatic pilot re-lighter automatically senses the absence of a pilot flame and starts to spark until it senses that the pilot has been relit.  These are NOT electronic spark ignition systems.  These were installed on only standing pilot furnaces (the ones where the pilot is always on).  Here’s why they’re dangerous in my opinion.  And I know for a fact that they are, because I spoke to a gas man who got blown across the room because he didn’t understand how that system worked.  If the thermostat is calling for heat and you turn the gas control knob from the on position to the off position, the pilot light and the burner flames both go out.  But like the gas man, if you then immediately turn the knob back to the on position, the thermocouple device is still hot and will immediately allow gas to flow into the burners BEFORE the pilot light is relit.  A very large volume of gas enters the chamber and when the pilot finally does light, you have a fairly good size explosion.  And  you’re at the epicenter of it (like the gas man was).  If you’re having a problem with frequent pilot outages, the cause of the pilot outages needs to be diagnosed and corrected, rather than installing one of these re-lighters.  The standing pilot system can also be converted to an electronic spark ignition system as well (which will save on gas usage too).  I realize that gas company technicians are not furnace technicians.  But it also occurs to me that they know at least as much about furnaces as the average homeowner.  And it scares me that a homeowner could easily make the same mistake the gas man made.
  5. Flat, (horizontal upflow) cooling coils with very narrow condensate tracks running under them to catch the water.  The manufacturer of this coil learned fairly quickly what a disaster this coil was.  These very narrow troughs clogged up with gunk and water would run down into the furnace.  And you could not clean the face of the coil either.
  6. Outside A/C units with horizontal condensers where the coils were facing upward.  Hail storms would often flatten the entire face of the coils.  Imagine how a car radiator would fare if you laid it out horizontally in a hailstorm, and you’ll get a pretty good mental picture of the carnage.
  7. Outside A/C units with one piece vertically configured condenser with the hot air exhausting out of the upper of the part of it on the same side as the inlet air.  These used a double-shafted (expensive) condenser fan motor with 2 squirrel cage blower wheels.  The hot, exhaust air would get sucked right back into the condenser inlet.  As a result, the A/C system had to run much longer and work much harder to cool the house.
  8. Plastic refrigerant hoses running from the outside A/C unit to the indoor cooling coils.  They leaked like a sieve. 
  9. Plastic flue pipes on some of the older furnaces with really hot flue gases. The plastic gave out causing dangerous flue gas leaks.
  10. Setback thermostats with little battery operated clock motors in them.  Many of these even had proprietary batteries that ran the clock motor.  You would set these little pins in the appropriate position for the time you wanted the temperature to change.  But they’d typically get stuck in the wrong position.
  11. Furnaces that pulsed the combustion system.  Big recall due to flue gas leakage.  The design was abandoned.  (Lots of them still out there and working okay though).
  12. Combination hot surface igniter and flame sensor in furnaces.  The hot surface igniter also served as a flame sensor.  It didn’t work out, and the conversion kit to convert the furnace into a conventional design cost an arm and a leg.
  13. High efficiency, high voltage electronic air cleaners that caught fire when the high voltage arced and ignited the plastic inside them.
  14. Self washing, high voltage electronic air cleaners.  These were monster size boxes, almost as big as a furnace.  They had water and a drain system plumbed to them.  They actually washed out the cells.  I only saw 2 of those – the electronics were fried years before in both for obvious reasons.
  15. Humidifiers that sprayed water into the ductwork.  No explanation necessary.
  16. High efficiency A/C system made in the early 1980’s.  Very few of these were sold (luckily).  The contraption I saw was about 5 feet tall and 4 feet square, and this was merely the smaller 2.5 ton version.  It had a little tiny fan motor up in the top, and a tiny little compressor down in the bottom that looked lost in that expansive area.  The problem was that the volume of refrigerant in the system was over 15 pounds and the little reciprocating compressor just couldn’t handle it.  So they ate compressors for lunch.  I did a warranty compressor replacement on one of these, but only under the condition that I would add numerous devices to ensure the survival of the replacement compressor.  The system lived a long, happy life after that, and was extremely efficient by early 1980’s standards.  These were only made for one year for obvious reasons.
  17. Rheostat control in the outside unit that varied the speed of the condenser fan motor as the temperature varied.  These controls had a very high failure rate.



Current devices


  1. Three layer, sealed, permanent “washable” furnace filters.  You can’t wash the middle layer out.  Dirt continues to accumulate in that uncleanable center layer until it finally kills the system airflow.  One of these I’ve seen had another “novel idea” – a round, plastic whistle in the middle of it.  The whistle was supposed to whistle at you through the ductwork when the filter became restricted and needed to be cleaned.  (Dirt plugged up the hole and it never made a peep).  The whistle also protruded out a ways, and it would get caught and pulled apart when you inserted or removed the filter through the filter slot, leaving a big round hole for dirt to go through the filter.
  2. After-market “water assisted cooling device” for outside A/C units.  These spray water on the outside unit’s condenser coils on demand to help it work more efficiently.  Not a bad idea if you use distilled water.  The problem is that the mineral build up can mess up the heat transfer through the condenser by insulating it.  When this occurs, it can’t remove as much heat.  Then you have big problems, especially if you can’t remove the scale – without damaging the condenser.  Air cooled condensers aren’t designed to be used as waterfalls.
  3. Electrostatically made/treated filters.  Some disposables have this feature and some of the permanent ones have it too.  It’s supposed to give you better particle trapping efficiency.  These are supposed to create like a “static cling” effect when the air moving through the furnace filters causes the fibers to move around.  So the dust particles will supposedly be captured more efficiently.  The problem is that in literally no time at all, a fine coating of dust covers them and disables/insulates the static field.  You still have filtering, but you lose that extra amount of filtration afforded by the electrostatic.  ASHRAE (our rating standard) prohibits the filter manufacturers from including the  slightly higher initial particle trapping rates in the filter’s MERV (particle trapping efficiency) rating for this reason.
  4. Sticky filter sprays.  You buy this in a spray can.  It makes the surface of the filter tacky/sticky.  It’s called a “tackifier”.  Same problem as the electrostatic methods – it doesn’t work once the dust covers it.  But at least if you’re industrious enough, you could keep taking the filter out and respraying it from time to time.
  5. I know I’m going to catch some flack over this one.  But sometimes you just gotta.  Not all my colleagues agree with me on this.  AIR CONDITIONER COVERS.  I’ve seen some MAJOR disasters occur when the system got turned on with the cover on it.  That can really mess up your unit when it happens.  Don’t’ think it can’t happen.  You could be the only person who knows that cover’s on there.  So if you have a house-sitter while you’re on vacation or you’re in the hospital, etc. it can happen.  And an electrical malfunction can also turn the outside unit on without the thermostat even being turned to the cool position.  Obviously you could turn the A/C breaker off when you put the cover on it, but if you don’t remember to turn the power back on to many units 24 hours in advance, they can be damaged the first time you turn them on.  I saw a setup at a customer’s house once that was pretty ingenious.  The lady had a piece of screen with a couple of 2 by 4’s on each end laid over the top of the unit.  So if it did come on, the air could at least move through the screen.
  6. After-market replacement silicon nitride hot surface igniters for replacing OEM silicon carbide igniters.  I understand that some of these designs work better than others.  But the first and second long, skinny, stick shaped models I tried only worked for 8 days, and 2 weeks, respectively.  These were supposedly “appropriate replacements” for the silicon carbide igniters I was replacing.  For those of you that don’t know, silicon nitride igniters typically last a lot longer than silicon carbide igniters.  But most silicon nitride igniters are being powered with only 70 volts, whereas the typical silicon carbide igniters are being powered with 120 volts.  But the manufacturer of the after-market replacement silicon nitride igniters claimed that their design would allow the use of their igniters in a 120 volt circuit.  But I found that both of the ones I had purchased split down the middle from the combined heat of the flame and the extra voltage that makes them run much hotter in a 120 volt vs. a 70 volt power environment.  After discussing this later with some friendly competitors, I learned that I got out lucky.  They had purchased dozens and had experienced the same issues I did.
  7. Direct drop-in replacement refrigerants for R22 systems.  Some of these come with a penalty of less BTU output of cooling power from the A/C system. 
  8. Cheap “home improvement store” pleated furnace filters.  These can literally destroy your furnace and A/C unit.  The restriction to airflow is unbelievably high, and to make matters worse, the frames are extremely flimsy.  They end up warping and allowing dirt to pass around them, which can damage your system.  I’ve seen several of them turn into sails and end up getting stuck in the blower motor, where they can wreak all kinds of havoc.  See the furnace filter tutorial page for more information.
  9. “Intelligent” gas control valves.  We jokingly refer to them as “dumb valves”, especially when they don’t work properly.  These are gas control valves that actually contain a processor.  These have a history of problems.
  10. Computerized humidistats.  This is a really neat concept.  Hopefully they’ll get the bugs ironed out someday.  The humidistat has a processor that automatically adjusts the humidity setting for your furnace humidifier as the outdoor temperature changes.  I’ve seen a lot of problems with these systems.  Granted, some of them were not properly installed per the manufacturer’s instructions.  But others were and many still failed.  The remote (outdoor) sensors fail a little too often for my liking.
  11. 1” thick electronic air cleaner filters.  These just don’t have enough surface area to be effective.
  12. Central steam humidifier systems.  This is another fantastic concept.  But like anything else, it’s a better idea to wait until they iron the bugs out, especially all that racket when they vibrate the ductwork they’re mounted to and the water leaks.  And they’re extremely expensive units too, typically costing up to 5 times as much as a conventional humidifier.  I saw one brand that actually cost ten times as much as a conventional unit.  But when they’re properly installed, they can humidify your house using a small fraction of the water used by a conventional humidifier. 
  13. Electric/pneumatic damper controlled residential zoning systems.  When properly installed with good quality components and adequate ductwork these systems have a lot of potential for people unlucky enough to have only one system for a large 2 story home that really should have been built with 2 systems.  So far I’ve been sorely disappointed, having only seen damaged equipment and poor performance, typically much worse than you’d see with a 1 system configuration without the zoning installed.  The problem is usually that there just wasn’t enough duct capacity to support the dampered zoning system, and no easy ways to add more.  So you’re left without much to work with when configuring the zoning system.  There are numerous workarounds, but the extent to which they can be applied is limited in scope when the duct capacity just isn’t there.  The A/C system and furnace both need x amount of airflow per minute moving through them.  And they aren’t happy campers when they don’t get it.  They’ll voice their disapproval by rewarding the energy companies and/or repair companies with more of your hard earned cash.  Some of the commonly used, manufacturer recommended workarounds result in decreased BTU output and/or decreased efficiency.
  14. Drum type humidifiers.  These have a motor that turns a media wheel through the same water, i.e. no water flows through them and goes down the drain to keep gunk and mineral accumulation at a minimal level.  They use a float mechanism, similar to the ones found in a toilet to maintain the water level at a specific height in the humidifier.  But just like toilet floats, the float ultimately fails to shut off the water.  So the tank overfills until the water reaches the overflow hole and  (if you’re lucky) runs out a drain hose.  When that happens, water goes straight down the drain 24/7, like a toilet that keeps running.  If the hose clogs, the water goes into the ductwork and sometimes the furnace and rots them out, before ultimately ending up on the floor.  But at least the humidifier is getting purged of some of the built up stuff when that happens.  Very few of us in this business have installed these type units.  Most of them we see were sold through department stores or home improvement stores.  We on the other hand typically prefer the “flow through” models where all the water drains out of the humidifier via gravity when the furnace turns off.  And that’s the type most of us have on our own systems, because we don’t need to “drum up” business at our own house.
  15. Hog’s hair media, permanent, washable filters.  These aren’t really made of hog’s hair – they just look like it.  These are better relegated to use for “door mats” to wipe your shoes on than for air filters.  They are just too limp to maintain their shape, because they have no frame around them.  So they tend to curl up around the edges and let all the dirt bypass them.  So if you have one of these in your system, replace it with a real furnace filter.  Then cut the hog’s hair one into the shape of a hog and put it on your stoop.
  16. Paper humidifier water panels, AKA humidifier filters.  This product is so bad that the results are almost comical.  Humidifier water panels typically reside in a vertical position inside the furnace humidifier and are honeycomb shaped.  So the water dribbles into the top of them and runs down through them via gravity in diagonal back and forth downward paths.  These are typically made of thin, flat aluminum with a “wetting agent” applied over it.  The home improvement stores are now selling these cheap replacement models that have paper attached to a honeycomb shaped, extremely thin wire frame.  So what happens when you keep running water over paper?  The paper goes bye-bye.  You look in there and you see what looks like a partially decomposed skeleton of a frame made of trash bag tie wires with the paper stripped off them.  So the water coming in the top of the humidifier just falls directly to the bottom of the humidifier without evaporating.  But where did the paper GO?  I found the answer to that question immediately when I saw a humidifier leaking water, because the drain hose coming out the bottom was plugged up with PAPER.  It wouldn’t be so bad if they at least stated on the box that they were paper.  Some tell you that you should change them twice per heating season.  They just don’t tell you why they should be changed twice instead of once per heating season.  Being a somewhat artistic person, I can think of one good use for these.  You could create a paper sculpture by controlling the rate of water flow into the top at varying rates from side to side.  So it’s artwork created by the process of removal over time – like woodcarving or sculpting.  Then you could paint them and sell them as “water panel art”.  Paper has its uses.  It just doesn’t work well in some applications involving water, which is why we don’t see much paper swimwear.
  17. “Roman Hat” flue caps.  The last thing in the world we want to happen to our flue gases coming out of the flue on the roof is for them to be forced back down the flue pipe by the wind.  This can cause the flue gases (containing carbon monoxide) to come out of the appliances inside the house.  At the very least, it will blow out the pilot or cause nuisance lockouts on newer equipment.  Oddly enough, the Roman Hat flue caps were designed to prevent that, but more often than not, they cause it.  These things look like the battle helmets worn by the Romans, hence the name “Roman Hat”.  The idea is for them to work like a wind vane, and turn the opening where the flue gases escape in the opposite direction from the way the wind is blowing from.  But the flue system is a very hostile environment and eventually the Roman Hat ends up permanently stuck in one position due to corrosion of the pivoting surfaces.  And obviously a wind coming from the direction the opening is facing is going to force the flue gases backward when that occurs.  I’ve also seen these attached to fireplace flues on the roof as well.
  18. Rooftop attic ventilation turbines.  These were initially thought to be energy saving devices.  But I’ve seen studies indicating that in many cases, they can cause you to use more energy.  And they typically don’t provide as much ventilation as the standard 8” round attic rooftop vents they replace when no wind is blowing or when they get stuck and won’t turn.  Contrary to popular belief, the primary reason why codes mandate attic ventilation is to ensure that we don’t end up with condensation in the attic during the winter.  Yes, the attic ventilation does also provide the added benefit of removing some of the heat from the attic in the summer.  But its primary purpose is to prevent winter attic condensation issues.  If you have inadequate attic ventilation, the moisture from the living area can migrate up through the attic as humidity contained in the air in the winter.  And when it reaches the much colder surfaces in the attic, the relative humidity of that migrating air skyrockets.  When it reaches 100%, it condenses on the building materials in the attic.  A properly sized attic ventilation system prevents this from occurring by creating a continuous flow of air through the attic, though inlet vents and outlet vents.  The problem is, that if the turbines don’t turn, they provide less of an escape route for the attic air than the standard 8” roof vents do.  So we can end up with inadequate air movement volume to prevent the attic condensation from occurring in the winter.  And here’s the other totally different problem in either winter or summer.  The faster the outdoor wind speed is, the faster the turbines rotate.  Keep in mind the fact that the inlet openings where the air enters the attic are a fixed size.  The faster the turbine rotates, the more of a negative pressure it places the attic in, because it can’t move enough outside air into the fixed size air inlets.  Here’s what happens then:  A portion of the air from the living area that you’ve already paid to heat or cool is literally being sucked up into the attic and forced out of the attic through the turbines on the roof, running your energy bills up by making the furnace or A/C have to run longer.  Ideally, the attic should be fairly well sealed off from the living area, but that is rarely the case, especially in older homes with ceiling mounted can lights, bathroom fans that terminate into the attic, unsealed common areas between the living area ceilings and attic floor, etc.
  19. Power attic ventilation fans.  These are not what we call “whole house fans”.  These are typically fan systems that blow the air out of the attic.  It’s like a powered version of the rooftop turbines previously mentioned.  These units are typically installed with adjustable thermostats that turn the motor on automatically when the attic reaches a certain temperature.  And the thermostat is likewise supposed to turn it off again when the thermostat senses that the attic temperature has dropped x number of degrees from the setpoint.  The problems here are twofold.  First, they are subject to the exact same problem as the turbines, i.e. they can put the attic in a negative pressure and cost you more energy dollars.  And secondly, studies have shown that these fairly large motors use more energy than you save by getting that heat out of the attic.  But then someone came up with a very clever invention – a solar powered attic ventilation fan.  The problem was that the initial cost of the unit was so great, it would take it 20 years to pay for itself in the form of reduced cooling bills.  
  20. Foam filled A/C condensing unit pads that the outside unit sits on.  These are very lightweight pads with some type of foam covered in plastic.  They just aren’t strong enough so they collapse and come apart.
  21. “Duct boosters”.  These are small, inline blower systems, typically designed to be installed in a duct serving an area that is hard to heat and/or cool, usually due to a lack of adequate duct capacity serving that area.  I’ve seen quite a few of these, but have yet to see one perform effectively enough to justify the initial cost and the power consumption over time.  It’s typically just a drop in the bucket improvement scenario. 


Areas Served

Greater Kansas City including:

Johnson County, Kansas     Kansas City, Kansas       Kansas City, Missouri

Fairway, KS

Lake Quivira, KS

Leawood, KS

Lenexa, KS

Merriam, KS

Mission, KS

Mission Hills, KS

Mission Woods, KS

Olathe, KS

Overland Park, KS

Prairie Village, KS

Roeland Park, KS

Shawnee, KS

Spring Hill, KS

Stanley, KS

Stilwell, KS

Westwood, KS

Westwood Hills, KS


Copyright 2009 Leonard Arenson Heating & A/C


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