* Prices * Questions about your home * Frequently Asked Questions * 713.781.6090

The HVAC System

Photographs of the HVAC system found during home inspections.

Are you a real estate investor? Here is a resource page for real estate investors.

Back to the contents page for the home inspection photos

Heating Equipment

Energy Source:there are different types of equipment, so we report on the energy source here. Most common types of energy source in Houston are electric and gas heaters.

a. If the inspector deemed the furnace to be inaccessible:

 The ability to access the furnace area is needed to have a good view of what is going on when the furnace is on during an inspection. Another aspect of why this is reported can be workspace. If a technician does not have the space to properly work on a unit, he may not find everything that is wrong, but the cost of repair can be greater, since he could take longer to work on the unit in a confined area.

b.Temperature difference between input and output air: the average temperature of the conditioned air has the average temperature of the supply air subtracted from it. One issue is where are these measurements taken? Most home inspectors will take the temperatures at the vents and at the return chases. Air conditioning professionals will drill holes into the system near the furnace to insert thermometers just before and after the air has been conditioned. The temperature at the vent method will indicate issues with the conditioned air through the system. The temperature near the furnace method isolates issues closer to the furnace.

For the test performed, a range between 30F and 55F is acceptable.

c. Other findings

HVAC burner compartment
Heat from a gas fired unit comes from these burners in the furnace. The gas is ignited to heat the air down these tubes. Air from the home passes over these tubes to warm up. The tubes are the heat exchanger.





unstrapped furnace ventAttics with limited space cause situations where different items are pushed into the same space. Wiring for the alarm system was run too close to the furnace vent for my liking, but there is another reason for this picture. The furnace vent can become damaged during windstorms. High winds will push the vent or objects into the vent. This can cause leaks at the point where the vent penetrates the roof, but the movement could cause damage to the vent. Strapping the vent between the rafters will prevent such damage.

rust on the furnace ventAs mentioned above, furnace vents can become leak spots, so we check for water signs on the vent. With vents making turns to reach the furnace compartment, water can stay in an area on the vent. This leads to rust, which can cause holes or other damage to the vent. Combustion gas should not be vented into the space near the equipment. In the case of the photograph, the rust seen on the vent may not be from a roof leak. This equipment was located in a basement (yes, there are a few homes in Houston with basements for old boiler systems). There were signs of condensation issues occurring in this space, so the moisture on the vent could be from this cause.

unpai nted ventChecking the vent on the interior and its connection to the equipment is important, but checking on the roof is needed too. Vents are painted to protect them from rusting/deteriorating from exposure to the sun and rain. High temperature paint (frequently found in automotive supply stores) may be better for this application. In the photograph, we are looking at the side facing away from the ground where we find unpainted spots. The most common cause for this is that contractors paint what the builder and client will see from the ground, but not take the time to do the job right.

vent heightFor the last fifty years, the trend in home construction may be summed up by saying that safety was a concern, and the current trend in construction may be marked by efficiency. Having combustion gas expelled from the building has been done for some time (although not always); however, we now look at what happens to that gas once it leaves the structure. Many older vents simply forced the gas onto the roof surface.  Vent caps are designed to prevent the rain from coming into the home, but some combustion gas will still head down to the roof surface. This combustion gas can be hot, so the roof covering can be damaged, or in the worst case, a fire could occur. To prevent this from happening, vents are required to be higher off of the roof surface. Most homeowners may not realize that there vents have an issue, because various roof surfaces need different heights. With the slope of this roof, the rear part of the vent comes too close to the roof.



Cooling Equipment:

a. Proper performance by operating system when outdoor temperature is above

60F by checking the temperature difference between supply and return air:

Why above 60F?  I was told once that damage can occur to the unit when operating the cooling system during colder weather. This may be true, but there is a better reason. If the outside temperature is too cold, you will obtain false readings at the vents. The compressor could be so cold that the refrigerant is releasing its heat at the compressor, even when the system is not working. If the evaporator coil is in a cold attic, or if the ducts are traveling through a cold attic, heat from the conditioned air could be released from any of these points, even though the system is not working. For this reason, I place the exterior temperature on the second page of the actual report.

The formula for the difference is Average Temperature of Returns (Supply Air)- Average Temperature of Vents (Output or Conditioned Air)= the difference. See description above for the heater for methods that can be used to test the system. Instead of a furnace being the center, the evaporator coil becomes the center of the holes in the system for a technician. A range between 15F to 22F is acceptable for the test performed.


b. Noticeable vibrations in compressor fan:  Vibrations can occur due to the unit being unstable or to equipment in the compressor (mainly the fan) being loose.

Vibrations can indicate problems with the equipment that need to be investigated further.


c. Other findings

unit is called the compressor, condenser, or outside air conditioning
unit by various people. This is an older unit that still functions
well enough, but there are some issues. First, it needs to sit higher
off of the ground to prevent water damage. If you see the tubes to
the right, you will notice that the insulation is coming off of it.
This is the refrigerant line, and it needs to be covered. Another
problem with this unit is that it has not electrical shut-off. If the
electrical panel was on the same side of the house, the unit would
not need one. It is needed as a safety issue for working on the unit.


A shut-off for the electrical power to the compressor is needed when this unit is not near the electrical service panel (the breaker box). The idea behind this requirement is one of safety. A technician working on the compressor cannot have the power turned on by accident when he is working on it.  What you may nt realize about this shut-off is that the interior housing is not secure, so it is coming off when the cover is opened. This can be a safety hazard (sticking a screwdriver behind the cover is an electrocution situation) and damage to the parts (rain entering behind the cover). Another common issue is that the shut-off does not function; that it is missing parts; and the wiring may be unsafe.

HVAC in closet
Here is a unit in a closet. It was a tight hallway, and I was trying to find the best angle for the shot.


There are two plenums on an air conditioning system. The retrun plenum is just a box on one end. This is the plenum which distributes the conditioned air to the different rooms through the ducts.

safety pan
Underneath your evaporator coil is a pan to catch any water which does not go out of the primary. It is always a concern to see rust, because that means that water was in the pan. You also do not want to see debris in the pan, because this can clog the line. What is that I see? Burn marks on the evaporator coil around the cable entrance. Everything seemed fine now, but the homeowner knew nothing about this. She believed that it had been repaired by a previous owner.

insidecompressorThis is where the compressor and condenser are located in the exterior part of the cooling system. You can see the fins which have copper tubes running through them for the refrigerant. This unit has a housing to protect those fins. Rusting is occurring, and leaf debris in the housing helps with damage from moisture.

damaged fins

Damaged fins on an air conditioning compressor can cause the unit to be inefficient.

exposed coils evaporatorThe evaporator coil has coils with fins like the compressor, but his takes the heat out of the home’s air to have the temperature go down. These coils are not usually seen, since a housing covers these coil ends. Will the coil ends become damaged if not covered? That is possible, but a good reason for the cover is prevent exposure of the coils to the air temperature of the attic. The coils will be taking heat out of the attic as well as the home, making the appliance run inefficiently.

burn marks on evaporator coilHere we have the housing in place. The thin copper line is the hot refrigerant line, while the line on the right with insulation on it is the cool refrigerant line. What is unusual is the soot marks on the housing. To take this apart to determine cause is beyond the scope of the home inspection, so the home inspector will call for further investigation.

evaporator coil dustThere is not often access to examine the evaporator coil, but many technicians include an access panel in a plenum to be able to clean the coil fins. This evaporator coil is covered in dust, which makes the unit work harder, reducing energy efficiency.

hot refrigerant line on framingOne issue that I report on is if the refrigerant line is touching another object. The cold refrigerant line touching another item can lead to condensation of the moisture in the attic air. The hot refrigerant line can burn into objects that it touches. This does not happen in every situation, but when this line was moved, the framing had a black mark and smooth surface from the heat.

safety pan for the air conditioner

The safety pan sits under the evaporator coil, which is where the refrigerant cools the air of your home. This process causes condensation. This water should go out the primary drain line. If there is a problem, the condensate water will drop out of the evaporator coil, so the safety pan is there to catch it. When you see rust or stains in the pan, the cooling system has had a problem. As you can see, this pan has rust. The safety pan should have a drain to allow water to flow out. This drain is often placed over a window or pipe to allow you to see the dripping water, hence you know that your cooling system has a problem. This pan does not have that drain pipe. You see a white box on the pan. This is a switch. When the water level is too high in the pan, this switch turns off your cooling system. This kind of switch is often found in town homes or condominiums, where having a secondary drain is not always practical.

no pipe insulation on primary drain

In the picture above we see two primary drain lines for the cooling system’s evaporator coil. On the upper line, we can see that the black pipe insulation stops as the pipe was heading down into the insulation. This was a practice of builders, who did not want to fully insulate this line. The idea was that if the primary is in the attic insulation, the line itself was insulated. We want the primary drain line to be insulated in the attic, since the cold water running through the line, makes the pipe cold in a hot attic. Moisture in the air condenses on the pipe, which can then drip to the ceiling below. This will look like a roof leak. The builder did not cover this area with much insulation, then stored items and workers moving through the attic caused this line to become exposed.

AC compressor fence

I understand that people wish to hide their air conditioning compressors, but this can lead to issues. In the photograph, we do have a fence that hides; and the fence allows air flow, which is good. The problem here is service. To examine the units, I had to hop over the fence, trying to find a place to stand. How is a technician to work on the units when he has no space. Making the area enclosed by the fence larger, giving three feet of space between fence and unit, would allow for access; however, this is a porch with limited space. Having a fence that can be easily disassembled would be the best option here. The fence does not effect function, but the repair costs would be higher.

compressor on platformThis photograph was taken while I was standing on the ground, so you are looking at an air conditioning compressor on a platform about six and a half feet above the ground. The location is not an issue, but workspace is a problem. Simple repairs can take longer since a technician will have to be on a ladder. Longer repair time means higher repair cost. The other problem here is the items being stored up against the unit and vine growth impede the free flow of air around the unit while also causing damage.

window unitWindow units are a weak point in the home. There are usually gaps around the unit, which reduce energy efficiency. They can also be pushed in by thieves to gain access to the home. For the home inspector, window units are also a clue. When these are installed in an area, and the home has a cooling system installed, we will probably find that the cooling system is not working well, or that the cooling system was not well designed.

Duct System, Chases, and Vents 

a. Filter type: types could be disposable filters, lifetime filters (sometimes called eco filters, which are ones that can be washed), and high media efficiency filters

Locations:The more locations can be better, since air is being pulled from several areas of the home. Also, a central location can pull air through the home. My reason for reporting on location is that I found some people may not know where the locations are when the first move into a home.

Replacing filters monthly improves air quality and helps the functioning of the equipment.

b. Other findings


space for a return


This is the space left under a closet air conditioning unit (heater and evaporator coils can be placed in a closet, while compressors/condensers are outside). This is meant to serve as the return air duct, so do not store anything in this space.




wiring in return vent

One item which has arisen as a safety issue over the years concerns how fires start in a home, and how they can spread through the home. Electricians (and other workers) would use the available spaces to run wires (or other lines). The concern is that damaged electrical wiring could cause a fire. In the return case, the air being drawn through the vent can help increase the fire, while allowing sparks to travel through the system as well. There may be nothing wrong with the condition of the wiring, yet the potential is there, so this fact is reported on the inspection report. Solutions? The wiring could be removed from the chase (alarm systems are often placed in the chase, and these could be easily moved); however this may not always be possible. Consult with an HVAC technician, but two basic means exist to correct this situation: 1) run a flexible duct through the chase to attach to the return vent opening; or 2)a wall covering material, such as sheetrock, could be applied over the studs covering the wiring.

dust in return vent

In some older homes, return chases are nothing more than the stud cavity. This can be an issue if newer equipment requires a greater volume of air to flow into the air conditioning equipment. The issue in this photograph has to do with dust. Due to not installing a filter at the chase opening, dust has collected here. This is a fuel for fire, but this can also adversely effect the ar conditioning equipment.

two return vents

two plenumstwo vents in ceiling

Do your rooms have two vents for the air conditioning? Sometimes people see these vents, and they do not understand what is happening. One vent is called the register, which is the vent supplying air to your room. The other vent is connected to the other rooms, but not to any equipment conditioning the air. This is called a jump drive. As we make our homes tighter, we also have the tendency to isolate the air in the different rooms when the door is closed. To equalize the air pressure between rooms, we connect them through ducts. Sometimes these ducts are connected to a central vent, which may be placed near the return air vent for the air conditioning system. The photographs show two vents in a room; two large return vents in a hallway; and two boxes, plenums, in the attic. Often the jump drive system will be simpler with a duct attaching two rooms only. Do these vents need a filter? You will find builders placing filters in these ducts more for appearance. The filter in the return air line cleans the air; filters in a jump drive hardly ever need to be replaced. You do not need filters here, but there is an exception: if the vent was designed to hold a filter, it should have a filter- the idea being that the system design intended a filter. Why do you need this system? The main benefit homeowners will notice concerns opening doors. If the pressure is lower in one room, and the door opens into the higher pressure space, you will have to really tug on that door, which can be hard for small children.

floor ventFloor vents are not the standard in Houston (we have few homes with basements). You do find them in the Medical center area, or any section of town with older homes, but this was in a relative new construction. I do not have a problem with them in general, but I question the placement of this register. This is located in the kitchen area, where you want a conditioned space while prepping the meal, but you also have various pieces of equipment present. The builder placed the vent here as a way to condition the air of both the kitchen and neighboring breakfast area, with other options not being easy due to layout. This vent may need cleaning more often if you use the kitchen frequently.

rusted vent

Rusted vent covers are an indicator of moisture in the home. The question becomes: where does the moisture originate from? Bathroom vents could suffer from moisture that is in the room due to poor ventilation of the steam from hot baths and showers. In other rooms, the rust on the vent may be from moisture in the home. Baths, fish tanks, and kitchens can be a moisture source for other rooms. Lastly, the moisture may be coming from the attic. With vents, a roof leak may be the culprit, but we also may have condensation forming, because of different temperature airs mixing or surfaces.  The vent may not be well sealed or insulated in the attic.

uninsulated vent box in attic

Connected with the photograph above, we see the duct that supplies the conditioned air to the room vent (also called a register). Often builders would place insulation over this metal box; however, current practice is to have insulation on the box just like we find on the duct itself. Also, the box is sealed from having conditioned air blow into the attic. This box is not sealed or insulated, which can lead to what we observed in the photograph above: rust on the vent.

loose vent

The vent cover should sit flush with the ceiling to have the air properly distributed. This may not be a homeowner’s biggest concern, but this needs to be reported none the less. The other factor for concern is that the vent is not properly attached. It could fall off, or there may be a problem with the box in the attic.

flex duct damagecrimped return air duct

There is not always a great deal of room in attics. This makes organizing the ducts harder. One consistent problem in these cramped spaces is crimping the duct, which restricts air flow. You may better understand this scenario by thinking of your garden hose. Bend the hose while water is flowing through the hose, and you begin to limit the water that comes through. The same happens with air ducts. In the photograph, we see a return air duct being crimped on a framing member supporting the roof. This will make the air conditioning system work harder as the equipment has to pull the air through the system. Sometimes these bends, as in the first picture, have damage to the sheathing.

ductoninsulationHere the air conditioning duct is on top of the insulation. This can compress the insulation some (depending upon what the duct is made of factors how much weight will depress down), which can hinder insulation performance. However, the duct can develop kinks with people moving it about, which prohibits air flow. It is also easier to damage a duct when it is not supported. Another issue with this situation is condensation. The air in the duct will be at a different temperature than the surrounding air of the attic. The duct and insulation contact point in certain cases could become a spot where the two different air temperatures collide, which will pull moisture out of the air. This condensation then will appear to be a roof leak below.

porr duct sealingduct sealing at plenum

We loose conditioned air through improperly sealed ducts. Poor quality installations and damage to ducts educes the efficiency of our air conditioning equipment. Above left, we see a placard being used to re-create the wall of a missing section of duct. This section is now not insulated, as well as being poorly sealed. Foam board insulation would have been a better choice of material. The tape used is duct tape, which is inappropriate in this application (the silver looking HVAC tape is needed) Above right, we have a flexible air duct attached to the plenum. Here, electrical tape was used instead of the HVAC tape. Also, the connection was not well made, so sealing was an issue.

torn away insulationduct covering damage

Ducts are better if they are run in conditioned spaces. Then we would not need to worry about the surface of the duct being affected by a different temperature, leading to heat transfer and then inefficiency of the system. The sheathing covering the duct helps hold the insulation in place, but it is to a degree assisting in sealing the duct from the attic. Once the sheathing is damaged, further damage can occur, which leads to the picture on the left: almost no insulation covering the duct wall.

touching deuctsEverything touching? We have the air duct, furnace vent, electrical cable, and refrigerant lines all touching. Many attic spaces are tight, but situations like this should be avoided. The furnace vent will become hot when the furnace is in use, and the hot refrigerant line will be hot when the cooling system is used. These can damage the other pieces with their heat. On the other hand, the difference in temperatures can lead to condensation of the attic air moisture, which will look like a roof leak below.

© Frank Schulte-Ladbeck Professional Home Inspector Houston, Texas
Frank Theodor Schulte-Ladbeck
home inspector, TREC# 9073
Houston , Texas , 77063 United States
  • Partners

  • Interested in advertising on this site? Contact me through the request a quote page.
  • Your Comments
  • Pages
My Store

Canonical URL by SEO No Duplicate WordPress Plugin