ADJUSTABLE PITCH ROOF CURB – A Complete Guide!
By Nick Bombard & Abbie Stancato
Adjustable pitch roof curbs are a variation of Knockdown Curbs that can be customized during installation to suit a roof pitched up to 1” in 12” in ANY direction. There are many situations in which an adjustable pitch roof curb is preferable to a fixed pitch curb, especially if:
- The pitch is not known exactly.
- There are multiple pitches on the same roof.
- There is multiple rooftop (pitched) orientations on the same roof.
WHO CARES IF THE ROOF IS PITCHED… WHY DOES IT MATTER?
Uneven Weight Distribution… The first, most obvious reason is safety. A heavy rooftop unit placed on a roof with a steep pitch displaces the load on the curb and could cause the unit to crush or buckle the curb. Furthermore, intense winds increase the odds that a rooftop unit could tip and fall off a roof curb posing damage to property, injury, and/or death.
Vibration… A pitched rooftop could be affected in the long term by increased vibration from the angle of motors and compressors designed to be level. Excess vibration can also cause tubing connections to vibrate and loosen, resulting in the loss of expensive refrigerant. Uneven stress due to pitch could cause the compressor to vibrate loose causing un-necessary noise and damage. Lastly, fan motor bearings can untimely wear out causing fan noise & fan failure.
The Compressor… The motor inside the compressor requires oil, just like the motor in your car. If the unit isn’t level, then neither will the oil level inside the compressor. This can lead to internal parts on the high side of the compressor’s motor not being properly lubricated. The lack of lubrication can cause the compressor to overheat and run less efficiently. Additionally, there’s always some oil that escapes the compressor and travels with the refrigerant throughout the lines. It’s possible for the oil to separate from the coolant and pool in one area of an angled condenser section. As long as the unit is level, this oil returns to the compressor and gets redeposited where it’s needed. However, if the unit isn’t level, the oil may separate from the refrigerant and end up pooling in the lines and coils. Over time, this can lead to a shortage of oil in the compressor, causing damage and overheating. Additionally, oil coating the inside of the coils can make it harder for heat to transfer, decreasing the system’s efficiency. See “How Does An Air Conditioner & Heat Pump Work? – Basic HVAC Tutorial.“
HOW IS AN ADJUSTABLE PITCH CURB DIFFER FROM OTHER PITCHED CURBS?
Adjustable pitch roof curbs consist of two assemblies, whereas a fixed-pitch curb is one. The lower assembly gets attached to the pitched rooftop. The top assembly slides over the bottom assembly like a sleeve. The slope of the roof is easily offset by leveling the upper assembly, while the lower assembly remains fixed. Unlike a fixed pitched curb, which must be ordered with a specific pitch & orientation in mind, an adjustable pitch curb can simply be leveled on the spot with no prior pitch information.
WHAT IF I DO NOT KNOW THE PITCH OF MY ROOF?
If this applies to you, you’re in luck. All you have to do is confirm that your roof is pitched less than 1” in 12”, and you can install an adjustable pitch curb regardless of the specific pitch of the roof or the orientation of your rooftop unit. Please see our blog post about measuring the pitch of your roof if you have questions about measuring the pitch to discover if your pitch is more or less than 1” in 12”.
WHAT IF THERE ARE MULTIPLE PITCHES OR ROOFTOP UNIT ORIENTATIONS ON MY ROOF?
It is frequently the case that a roof will have a slightly different slope in certain areas. Sometimes these subtle differences can be difficult to measure, or it may be more convenient for you to find a single solution for all the different pitched curbs required. If you find yourself in a situation where you anticipate the need for multiple differently-pitched curbs for the same job, you can order adjustable pitch roof curbs to satisfy all your needs without worrying about the specifics.
Not all rooftop units face the same direction – Orientation… It’s common for units on the same roof to be rotated differently from each other. Without the availability of adjustable pitch curbs, this would result in the need to order fixed pitched curbs with different pitch orientations. You can, instead, order adjustable pitch roof curbs with confidence that your roof curb will work for the desired application regardless of the orientation of the rooftop unit.
HOW DO I ASSEMBLE AN ADJUSTABLE PITCH ROOF CURB?
Similar to knockdown roof curbs, adjustable pitch curbs ship disassembled. MicroMetl adjustable pitched curbs come in a single, compact package that includes all the required hardware. The sides and ends of the top and bottom assemblies are joined with sheet metal screws that fit tightly into pre-punched holes at the ends of each piece. The locations of the screw holes that hold each assembly together are specially embossed so that the heads of the sheet metal screws will have clearance as the top and bottom assemblies slide past one another during construction & setup. The embosses of the top assembly face outward, and the embosses of the bottom assembly face inward. The top assembly will be slightly larger than the bottom assembly.
When you’re ready to install the roof curb, fasten the bottom assembly to the roof. Make sure you measure the corner-to-corner distance in both directions, verifying that both measurements are the same, to guarantee that the curb is perfectly square. Then, the top assembly slides over the outside of the bottom assembly. The top assembly will be loose, allowing it to slide up or down. Lift up the lowest (downhill) end of the top assembly in order to make the curb level. Once the top assembly is level, self-drilling sheet metal screws (called “Tek Screws” — included) are screwed through the holes of the top assembly into the sidewall of the bottom assembly, locking the top assembly in place. Tek screws must be inserted around the entire perimeter of the curb to safely and adequately secure the sections. Once leveled and constructed, it’s time to install the duct supports and gasket in preparation for the rooftop unit.
ARE THERE HEIGHT RESTRICTIONS ON AN ADJUSTABLE PITCH CURB?
There is no upper limit for the height of an adjustable pitch roof curb, but there is a lower height limit. Because the top assembly slides over the bottom assembly to alter the pitch of the curb to match the pitch of the roof, the minimum height of the overall curb is dependent on the height of the lower assembly. The minimum height of the lower assembly is related to the length of the roof curb in its longest dimension. Since adjustable pitch roof curbs are intended for roofs with a slope up to 1” in 12”, the minimum height of the bottom assembly will be the length of the curb divided by 12, plus 1” of overlap for tek screw installation. We must also account for any clearance needed by the duct supports when the top assembly is placed onto the bottom assembly. For example:
70” x 40” roof curb
70” long dimension
70” / 12 = 5.83”
5.83” + 1” overlap for tek screw installation = 6.83”
6.83” + 1” clearance for duct supports (typical) = 7.83”
In this example, the minimum height of an adjustable pitch roof curb would be rounded to 8”. Of course, there is no reason that you couldn’t order a curb that was taller than 8” in order to meet your specific requirements.
Adjustable pitch roof curbs are an inexpensive and versatile roof curb option that can solve a variety of issues. They eliminate the need to stress over the pitch details of a certain roof. Adjustable pitch curbs remove the hassles associated with ordering the wrong pitched / orientation fixed roof curb. This catch-all roof curb design offers the peace of mind you deserve when facing a variety of situations & circumstances. Adjustable pitch roof curbs allow you to deal with uncertainty on the job site without breaking the bank, and without forcing you to custom order a more expensive job-specific fixed pitched roof curb. Most small-to-medium curb sizes are available as adjustable pitch curbs.
MicroMetl is the leader in HVAC Accessories and Energy Recovery. Please read the more elementary article “What Is An Adjustable Pitched Curb,” for a more basic understanding of Adjustable Pitched Curbs.
How Do I Measure For A Curb Adapter?
You’re on the roof to replace the Rooftop Unit (RTU). The unit nameplate is worn down to the degree that you can no longer decipher the model number, the brand or manufacturer. It is never practical to break the integrity of the existing roof to remove the existing Curb. Therefore, you must measure the existing curb and order a Curb Adapter. But… There’s a unit on top of it! That’s what makes this video a great bookmarking asset. Here’s what you need to do the next time you need to measure an existing curb with the HVAC unit atop of it.
How Does An Air Conditioner & Heat Pump Work? – Basic HVAC Tutorial
The History of the Air Conditioner
The air conditioner was invented in 1902 by the founder of Carrier Corporation — Willis Carrier. The primary design was for Humidity Control, not Temperature Control.
The Simplistic Definition of an Air Conditioner
An A/C system removes heat from inside your home and transfers it outside. This article is intended to explain the most basic functionality and operation of an Air Conditioner And a Heat Pump.
The Basic Physics Behind The Process…
Pressure and temperature are directly related. When a gas is under high pressure, the temperature of that gas increases. Inversely, reduce the pressure, and the temperature of the gas decreases. An Example: Water boils at 212° Fahrenheit at a standard sea level altitude pressure of 14.7 Pounds Per Square Inch. Go to the mountains where the pressure is lower, and you’ll discover that water boils at a lower temperature. The higher the altitude, the lower the air pressure, the lower the boiling point. The liquid refrigerant inside the system called R410A boils at only 55.3° Fahrenheit. As the boiling point of water is affected by changing environmental pressure, so are the boiling points of refrigerant in regard to the variance of applied pressure throughout an air conditioning system. This is the entire premise by which an Air Conditioner operates.
Two Basic Parts of an Air Conditioning System
Most home split system air conditioners have two basic parts: an Outdoor Unit (Compressor – Condenser Coil – Fan) which sits next to your home and an Indoor Unit (Evaporator Coil – Expansion Valve – Fan) that’s connected to a central duct near your furnace.
The thermostat inside your home is set to 75°F. When the temperature inside the home exceeds 75°F, a fan inside the home turns on. Its purpose is to draw air from inside the home, into the ducts leading to the Inside Unit while forcing air through air ducts into the rooms of the home. As air is moved throughout the Inside Unit, it’s forced through a winding tube section called an Evaporator Coil / Heat Exchange Section. This evaporator coil is where cold temperatures are introduced to the air inside your home. It reduces the temperature of the incoming supply air.
So how do the cool temperatures get there? Let’s start with the Outside Unit containing the Compressor, Condenser Coil, and Fan. As the refrigerant travels throughout the AC System, it repeatedly changes from a gas to a liquid state.
The R410A refrigerant is in a gas state as it enters the outside unit. The gas enters into the compressor, which pressurizes the gas. The gas enters the compressor at about 50°F. As it exits the compressor it succumbs to a substantial pressure/temperature increase. The gas increases in temperature to approximately 150°F. If you’ve ever noticed all the very delicate air fins creating the walls of the Outside Unit, you’re looking at the condenser coil. The gas enters the coil and is snaked through the long winding coils throughout the outside of the unit. The fan on top of the Outside Unit draws outside ambient temperature air through the coils to remove heat, dispelling it through the top. Place your hand in the air stream of the fan output and you’ll experience just how much heat is being removed. By the time the gas makes its way through the coils, it has cooled to a liquid state. It is still under high pressure and still relatively hot… About 100°F. I’ll bet you’re wondering, how can it become a liquid when it’s 45°F above its boiling point… It converts to a liquid due to the high pressure exerted upon it at that time! The liquid travels through a tube from the Outside Unit to the Inside Unit.
This 100°F liquid encounters a device called an Expansion Value. This valve is designed to reduce the pressure of the refrigerant… cooling the liquid. Removing the pressure has the effect of lowering the temperature of the refrigerant. The departing temperature of the now liquid refrigerant is approximately 20°F as it enters the Evaporator Coil. The cold R410A Refrigerant travels through the Evaporator Coils and begins to cool the air of your home blowing across it. The coils produce approximately 55°F air. Therefore, the warmer 75°F home air is absorbed into the liquid refrigerant causing it to reach the boiling point where it returns to a low temperature – low-pressure gas state. The gas travels back to the compressor outside, and the process is repeated.
Facts And Maintenance Tips
- Most A/C Units are only capable of only a 15 to 20 temperature differential – In layman’s terms, if the outside temperature is 95°F, the best you can hope for inside the home is 75°F to 80°F. Therefore, any lack of maintenance will cause your system to be less effective and cost more than necessary.
- According to the Department of Energy, 78° Fahrenheit is the sweet spot for air conditioners to balance energy savings and comfort when people are at home and need cooling.
- An A/C system is a closed system. Meaning unless there is a leak somewhere, the fluid inside should always be present and will not dissipate.
Maintaining The Condensing Unit
- Clean The Condensing Coil and Protect Those Delicate Air Fins… Now that you understand how the system operates, you should understand the need for simple maintenance. Lawnmowers and weed eaters are the two of the biggest foes to your system. Remember, the air is being sucked to the inside of the condensing unit. Grass, cottonwood, leaves, and any direct contact which damages the fins reduce airflow across them is costing you money. A simple water hose and/or shop vacuum can easily remove much of the dirt and debris.
- Keep pets away… A pet’s urine is very acidic. it can cause serious damage to the coils over time.
- Protect the incoming (suction line), and outgoing (liquid line) copper lines… A typical residential AC unit has two copper lines which both exit the building’s exterior and run to the Outside Condenser Unit. Only one of these copper pipes, the cold line, needs to be insulated. This is called the suction pipe and is typically the larger of the two. Insulation will prevent outside heat from affecting the temperature of the incoming gas going into the compressor. There is no need to insulate the smaller, warmer copper pipe, often called the liquid line.
Replace Air Filter
- A dirty filter will restrict airflow across the evaporating coil. Replace filters regularly!
What is a Heat Pump?
We have all heard of Heat Pumps, but what are they, and how do they relate to an Air Conditioner? A Heat Pump is basically an AC system in reverse. I previously noted the heat you feel in the summer when you place your hand in the air stream of the exhaust fan of the Outside Condenser Unit. When the cooler days of fall and winter hit, a Heat Pump system reverses. It sends the cold temperatures from inside the home to the outside unit. That’s why you’ll see ice on the Outside Condenser Unit in the winter months. Heat Pumps are cost-effective because they don’t require a dedicated furnace. The problem with Heat Pumps is that they can’t often handle very cold temperatures without the assistance of an electric heating coil. This method of heating is very expensive during very cold winter days and should be considered when choosing between a Heat Pump and a dedicated furnace.
Who We Are
This article is courtesy of MicroMetl Corporation. Established in 1965… MicroMetl is the leader in HVAC Accessories. Specialist in Commercial HVAC Accessories & Energy Recovery.