Forced Warm Air
There are two basic ways of heating a home; radiant heat room by room, or a central heating system. Radiant in each room can be electric, wood stove, gas heater , kerosene, coal, a fireplace, etc. Central systems can be hydronic, steam or forced warm air. Hydronic and steam are detailed under hydronic elsewhere in this site.
A forced warm air system uses ductwork to distribute heated air from a source (furnace or air handler) to each room. The furnace can produce heat from any number of fuels; gas, oil, electricity, wood, or coal, or a combination of any fuels. An air handler will use a hot water coil to produce heat
Unless fresh air is piped in from outside of the home, the system will re-circulate 100% of the air it supplies. This means it must obtain air from the home by way of a return air duct or ducts. Properly installed, a warm air system becomes a loop by which air is drawn from the living space through return ducts to the furnace, heated, and sent back to the same space through supply ducts. The advantages to this type of heating system are numerous.
The air can be heated, cleaned, sterilized, humidified, or cooled (central air conditioning). If return air ducts are strategically located, the will reduce heat loss by recycling the warmest air back in to the system that collects at upper areas of the house
Supply ducts located around the outside walls of the rooms will temper the cold air as it infiltrates the home and reduce any discomfort from the air flow to a minimum.
The disadvantage is that ductwork takes up space. When installed by an experienced contractor, the ductwork will take up minimal or no extra space, and literally disappear into the framing of a house.
The heat loss, zoning, and cfm calculators in this site were designed for forced warm air systems, but will work for all residential applications.
Wood Furnace
A wood furnace or coal fired furnace burns wood or coal in a sealed firebox to heat an exchanger. With the help of a blower air is forced over the exchanger and ducted into the space. It’s basic components include the cabinet or jacket, firebox, blower, access doors for stoking and cleaning, and a small blower to fan the fire when more heat is needed.
Accessories for a wood furnace can include: electronic air cleaner, high performance media filter, humidifier, evaporator coil for central air, and a coil to make domestic hot water. Sometimes a condensate pump will be used to dispose of the water produced by the dehumidifying action of the air conditioning.
Due to high temperatures in the supply plenum, extra precautions must be taken with regards to air conditioning, evaporator coils, as well as ductwork clearance from combustibles. Be sure to check the manufacturer's recommendations.
A combination wood furnace will include an oil or gas burner, or electric elements as a backup.
Proper sizing of a wood furnace is very important for comfort and performance. Btu output and blower size should not be guessed at but should be professionally calculated. Air distribution is also critical and just as involved as any central heating system, if not more so because of building code requirements. If the system isn't correct, the accessories won't work properly either. The air filter, humidifier, air purifier and central cooling should match the system and will not accomplish their task if the furnace is too big. |
What are the causes of insufficient air flow?
The cause of inadequate air flow for the outside unit or condensing unit is primarily due to dirt on the coil. This dirt can be entrapped in the coil and you may not even see it. Take a flashlight and shine through the opposite side of the coil to examine the coil correctly. This dirt blocks the air flow and lowers the heat transfer. This condition causes the compressor to work even harder. The energy consumption of the compressor increases dramatically as the pressure in the outdoor coil in the refrigerant increases resulting in increased stress on the compressor. The compressor motor temperature increases dramatically. This of course can cause the compressor to have a very short life span as the windings of the motor of the compressor begin to deteriorate. Other less common problems that can cause the condensing unit to have insufficient air flow is the outside fan motor not operating or not operating at the correct speed. Also something placed against the condensing unit or the condensing unit being located too close to a wall results in poor air flow. For this reason the condenser coli should be cleaned thoroughly annually using high pressure but being extremely cautious of not bending the fins on the coil. If you should find the fins bent over for any reason take a knife or a fin comb and straighten them immediately.
The biggest single cause of insufficient air flow on the indoor unit coil or air handler is due to a duct system that is undersized or poorly distributed. This is generally caused by poor design of the duct system and/or not enough indoor registers or grilles or diffusers. This is a problem that should be addressed immediately and corrected immediately. The outdoor unit should be turned off until the problem is corrected. To determine if the duct system is incorrectly sized request our Duct Design Form by email and you will be able to analyze the duct system and see if it is designed adequately with large enough ducting and sufficient diffusers or wall or floor registers.
The second biggest cause is oversizing of the heat pump system. For example let's say your house had a 2 ton heat pump. Somebody decides that maybe it would be better to install a larger replacement system like a 3 ton system. It's the typical American attitude if the right amount is good then a whole lot more should be tremendous. The duct system remained the same and was never changed. The 2 ton duct system was marginal to circulate the 800 cubic feet of air per minute.
The new 3 ton system now requires 50% more air than the 2 ton system or 1200 cubic feet of air movement through the duct system in comparison to 800 cfm from the 2 ton system. Because the duct system was never examined for it's capacity before the change out occurred, the new 3 ton system begins to slug the compressor from the first day it is installed. A qualified technician can take temperature and pressure and air velocity readings and find this as a problem from the beginning. If the contractor selected the system and made a mistake he's likely to own up to it. So what the technician may attempt to do is increase the air speed on the indoor fan to try to compensate for the undersized duct. What will most likely happen then is the indoor fan will start huffing. Huffing is a condition that occurs when the fan capacity is increased beyond the capacity of the duct system and results in a build up of air pressure in the duct system. The amperage detector on the electronic fan controller senses this increase in current draw and slows up the motor. So the noise in the air handler and duct system will increase for a second or two and then get quiet repeatedly. This will continue to do this until the problem is corrected. If your duct system is huffing most likely this is the cause of the problem. This problem is easily avoided if the duct system is analyzed before the new system is selected and installed.
Poor maintenance on the system such as dirty air filters, dirty indoor coil or blower in the indoor unit will result in inadequate air flowing over the indoor coil. The indoor coil should be inspected as well as the blower and cleaned at least every 2 years. Another problem is closing of the dampers at the registers or grilles in the house for most of the diffusers in the wall or floor. The result is improper air flow and slugging.
A system that has too much refrigerant or overcharged will also slug the compressor.
The proper method of checking the system operation is to have a certified technician check the superheat of the compressor. This is the first test that will determine if in fact there is an air flow problem. Similar to taking your blood pressure and your temperature at the doctor's office this would be the first diagnostic test performed by a technician.
Let's examine more closely the results of slugging or liquid coming back to the compressor instead of gas. Over 95% of compressors returned under warranty to Copeland and other manufacturers are not defective due to poor workmanship or defective components. The compressors failed because they were slugged and the liquid literally killed the compressor. That translates into over 80% of compressor failures were due to slugging because of improper installations of either oversizing the equipment or a poor duct design. Every week the top trade magazines post problems with improper duct design, poor installation and leaky duct systems and oversizing systems as now in epidemic proportions in the HVAC industry. Epidemic meaning the vast majority. Your only remedy to stopping this problem happening to you is education. This problem is not usually due to contractors trying to gouge the public as much as it is due to ignorance. Our technical support deals with contractor questions everyday and we know this problem is not due to anything more than ignorance. Our tech support always asks the contractor in their first question when they have a problem is did they read the installation instructions that come with the equipment. 98% never even opened the installation instructions that came with the equipment to know what's happening. That problem alone could be discussed for many pages here but the only solution is for you to do your own installation following the guidelines we present or making certain the installer you select is following those guidelines.
Otherwise you'll become part of the epidemic problem of statistics of improperly sized and installed HVAC equipment and systems.
How does the manufacturer know what causes the compressor failure? Is this a new problem?
HVAC and compressor manufacturer's such as Copeland will randomly cut open returned compressors to investigate the reason for the compressor failure. They will perform what is called an autopsy. When a compressor has failed due to slugging there will be specific damage to certain areas such as the valves, piston walls and crankshaft and other areas. My own experience working in York International at their Advanced Engineering and Research department provided me with a wealth of information on HVAC systems and particularly the cause for their failures. Any compressor can have an autopsy performed to see what caused the compressor to fail. As it was true 36 years ago and as it is today, there were very few times a compressor failed because of defects in materials and workmanship. A compressor failure is the result of another problem in the system, not the cause of the problem.
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PROFESSIONALLY ANSWERED QUESTIONS
This page is designed to help people to complete their home improvement projects.
Below you can see a list of several pages every one of which is dedicated to a certain question answered before or to the one of the important stages of the project.
In order to gain accesses to any page please pay an access fee of $2.50. Just click on one of the “Buy Now” button below the topic you choose to buy. Once you pay, you will gain an instant access to the page!
Instant Access:
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First off, I just found your site and what a great resource! I'm finishing my basement and I've been trying to cobble together info on HVAC from all over the web, but I have found all the best info in one spot! I have purchased the cold air return and low heat instructions and should be putting them in next weekend.
So as I was hunting around the site some more, I saw the Leaking PVC quiz. I have this EXACT same issue! I would take a picture, but it would look exactly like the one on your site. It was much worse when the heat was on in the winter, but there is still the occasional drip.
Please let me know how I can fix it, thanks!
Matt
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 Finished Basement Edition is a book designed just for you! In this book you can find answers to your most frequently asked questions about ductwork installation in basement and more.
For more information please visit “Finished Basement Edition” page.
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Tap Takeoff into the Existing Duct
Hello Ed,
 I am installing a partition wall between mechanical room and the semi-finished part of the basement. The semi-finished part has carpet, painted walls. But, I do not intend to install ceiling.
I want to tap into the existing duct work for air-conditioning / heating.
Since there will not be any ceiling, I could just use round pipe and elbow to blow the incoming air from the top. For return I need to install something in the wall yet to be built. I am not familiar with all of different types of ducting parts and tools. Therefore, I was hoping that your website could be useful.
Any help will be appreciated, even if it costs.
Thanks
If you got a similar question please click the "Buy Now" button below and get the answer.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Duct Span Removal
On this page you can find a detailed explanation how to remove span of duct and how to put it back on.
This page has 3 pictures on it. Price for the instant access to the page is only $2.50.
On this page you can find an answer to this question:
Hello, Ed!
I am doing some structural work in my basement and the only way to get in the steel is to take down a span of ductwork, or to cut it. It looks like I can take out the piece I need to, it's about 3 feet long, on one end is an elbow that turns it upstairs through the floor, and the other end it joins a larger network that comes from the furnace.
I'm not afraid of home repairs, but I am a novice when it comes to HVAC. Is this something I should be able to swing on my own? If so, how do I go about removing the bands that connect the pieces, removing the piece I need to get out of the way and later reconnecting it?
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Cold Air Return in Basement – this page gives a description of installation of the cold air return on the wall which is separating mechanical room from the rest of the finished basement. On this page, you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 18 pictures on this page. All installation is divided into six steps that represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Supply Register in Basement – this page gives a description of installation of the sleeve that is a necessary fitting designed to hold a supply register, which should be placed straight down off the main duct. On this page, you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 20 pictures on this page. All installation is divided into five steps, which represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Register Installation on Ceiling Tile – This page gives a description of installation of a register on a ceiling tile. On this page you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 14 pictures on this page. All installation is divided into four steps which represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Offset Calculation – this page is designated to the professional visitors of my website. There you can find explanations:
1. How to calculate an off-set situated between two existing ducts.
2. How to calculate an off-set from full size duct and why it's different.
3. How to mark out and cut the duct before it’s snapped together and why it’s important to do.
4. How to find the spots where take-offs should be cut in.
5. What to do if the width of the duct would be too big for connection.
6. How to calculate, mark out and cut the duct using as a riser and off-set at the same time.
There are 14 pictures on the page. $4.00.
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How to Extend a Heat Duct to the Floor - this page gives a description of installation of the heat duct in the wall, which separates mechanical room from the rest of the finished basement. On this page you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 16 pictures on this page. All installation is divided into four steps which represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Bath Fan Exhaust through Brick Wall – On this page you can find out how to run a bath fan exhaust through the brick wall. If you want to know easiest and fastest professional way of doing that, do yourself a favor and get the information for a discount price.
On this page you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 15 pictures on that page. All installation is divided into four steps that represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Cold Air Return from Interior Wall – this page gives a description of installation of the cold air return from the interior wall, which separates two rooms in the finished basement. On this page you can see pictures of all necessary tools and materials and pictures of the system elements installed. There are 19 pictures on this page. All installation is divided into three steps which represent the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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How to Drop a Register to Shallow Ceiling – On this page you can find another way how to drop a register to the soffit right below a supply duct. There are 19 pictures of all necessary tools and materials. All installation is divided into four steps, which represents the entire project in the making.
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
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Ductwork Insulation
www.energysavers.gov
Properly insulating air ducts located in unconditioned spaces such as attics, crawl spaces, garages, or unfinished basements can help improve your home's energy efficiency.
Air ducts supply conditioned air from your space heating and cooling equipment to your living spaces. They also return an equal volume of air back to the equipment to be conditioned again.
Ducts are typically made out of thin metal materials that easily conduct heat. Therefore, uninsulated or poorly insulated ducts in unconditioned spaces can lose through conduction 10%–30% of the energy used to heat and cool your home. The heating and cooling equipment then has to compensate for the heat loss and gain by conditioning additional air. This added conditioning raises a homeowner's energy bills. In addition, when ducts lose heat through conduction, rooms served by long duct runs can experience "cold blow" during the winter because they usually have lower heating-supply temperatures.
Ducts in conditioned spaces experience minimal conductive losses and gains since they are exposed to indoor air temperatures. However, these ducts may also require some insulation to prevent condensation on duct walls and to ensure that conditioned air is delivered at the desired temperature.
Credit: 30% of cost, up to $1,500
When and Where:
* 2009 and 2010 only
* Primary residence only
* Existing homes only
Materials:
R4 Duct Wrap Insulation Sleeve Insulation
R13 Wall Insulation “Silver” Tape
Staples
Tools:
Utility Knife Tape Measure
PC4000 - Heavy-Duty PowerCrown™ Tacker Templates
Before insulating, seal all the gaps around drive, pipe connections and take-offs. The best stuff for duct seal are special mastics or duct sealants. Do not use aluminum tape – it will not stick to old ductwork because they are covered with dust..........
Installation on the paid page might not exactly describe your upcoming project. However, it will give you an important example of how this type of installation should be done. In addition, it will open the gates for as many questions as necessary to make sure that the job is done right.
Please use "Buy Now" button below, pay $2.50 and get onto the page instantly!
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