What size supply duct for 3 ton unit

Discover the LG 3 ton split AC and DUALCOOL inverter AC and its features, including energy-saving tech, ThinQ AI, and fast cooling. ... Fuse Size(A) 25 Exterior Color Code Munsell 9.54Y 8.34/1.31 ... 3 x 2.5 POWER SUPPLY TO UNIT. Power Supply to Unit Outdoor POWER AND COMMUNICATION CABLE. Power and Communication Cable(No. × ㎟) 4 x 1 PIPING ...

Originally Posted by tigergrad97. 12" -14"...by appearance anyway. 2-14" would be ok for 3 tons (depending on length and bends/turns. So your a bit small for 3 tons if 1 is 12" and the other 14". Which may be why your current 3 ton struggles on some days. Reply. 11-10-2010, 09:09 PM #10. tedkidd. Professional Member*.The right size of return duct for a 3.5 ton AC is 22 X 22 inches. In the case of a 4 ton AC, it’s 24 X 24 inches. And for a 5 ton AC, the correct size is 27 X 27 inches. Calculate the return duct size. And multiply AC tonnage by 3.14 for round and 144 square inches. This is for rectangular ducts. Now, we have all the answers and calculations ...The Trane Engineered Products Rooftop is a packaged air, heating and cooling system, suitable for heating, cooling, ventilating and makeup air applications. Unit sizes range from 800 to 14,000 CFM (0.4-6.6 m3/s) with 1/2-15 HP. motors and 100,000 BTU/Hr to 1,200,000 BTU/Hr (29.3 to 351.4 kW) input. Duct furnaces are ETL certified for safety and ...In short, there's two prevailing standards that determine whether duct detection is required. The first (and most common in the United States), is the International Mechanical Code (IMC). Section 606.2 identifies areas where smoke detection is required for the purpose of mechanical unit shutdown. The other prevailing standard is NFPA 90A, the ...Now size the ducts and branches so that the velocity is 600 to 900 ft. per minute for sheet metal and 600 ft per min. Maximum for flex duct. (Example: a 7" dia. round flex duct has an area of 38.5 sq. in. {or .267 sq.ft.} and 140 cfm will pass through it with a velocity of 539 ft. per min.) This is rule of thumb information and experienced ...

Our previous 5 ton unit only had a 16x16 (leading to a 12 inch round) and a 12x12 (leading to a 8 inch round). We had many issues with our previous unit which i believed to be linked to our low return air duct sizes. In the 15 years we owned that unit we had to replace the condensor 3 times (about every 5.19 Jan 2021 ... Understanding the procedure of reducing the size of an air duct based on sound principles, not rules of thumb. Proper Duct sizing, no rules ...What size return air grill for a 48000 BTU heating system? 48,000 btus is equal to 4 tons of air flow, 12,000 btus per ton. You need 144 sq in per ton.Installation Figure 34. Cooling and gas/electric —10 tons high Figure 36. 4 to 6 ton high efficiency units, 6(074)-8.5 efficiency— horizontal airflow, supply and (Microchannel) high efficiency units and 6 to 10 return ton standard efficiency units - down flow supply and return air openings w/ through- the- base utilities 3 7/8"...Note: For duct pressure control, a Duct Static Pressure Transducer is included. However, 5/16- or 1/4-inch plastic tubing and a static pressure probe must be field supplied/installed approximately 3/4 down the longest supply duct run. Single Zone VAV - Series 100 is available for single zone variable air volume (VAV) ap-Air handler closet dimensions: Minimum of 30"W x 49.5"H x 32"D for small units and 39"W x 60.5"H x 36"D. Furnace closet dimensions: Minimum 26"W x 40"H x 42"D for small furnaces and 37"W x 46"H x 41"D for large furnaces. Of course, those are minimum dimensions, and the closet can be much larger. But these AC, furnace or ... In most cases, if you are installing ducts in each room where there is a supply, you will want to go with the same size as your supply vents. If you are installing just one or two return vents, you will want to go with a 12-inch return for 2-ton units and lower. 14- inches for 3 and up. 16-inch should be suitable for 4 ton systems, whereas 5 ...

48VL-E300603-TP 48VL = Single Packaged Air Conditioner and Gas Furnace System / Type of Unit-= StandardE = Major Series 30 = 2.5 Tons / Nominal Cooling Capacity 060 = 60,000 / Heat Input Size (Btuh) 3 = 208/230-1-60 / Electrical Supply-TP = Base unit with tin plated indoor coil hairpins (Single Phase Only) Single-Packaged Products with Energy-Saving Features and Puron® refrigerant.It has a 2 ton Skymark HVAC unit that produces 750 CFM for heat and 800 CFM for A/C. The unit is located in a bedroom closet. There are 2 supplies coming off the HVAC unit supply plenum: - 16 x 6 rectangular sheet metal duct feeding the bedroom. - 12 x 6 rectangular duct feeding the living room (and remainder of apt), fed by 9" flex duct …What return air duct size for a 3 ton AC? 18” for a round return air duct, and 16”x15” to 40”x7” for a rectangular return air duct. What size round return air duct do I need for a 4 ton AC? 19” in diameter, according to the return air duct size chart. Sizing Rectangular Cold Air Return Ducts6.4.2.3 "Fan units whose sole function is to remove air from inside the building to outside the building." (NFPA 90A, 2012, 6.4.2.3) Application Documents The International Mechanical Code (IMC) specifies that "If the space is air conditioned and the A/C unit is over 2,000 CFM, a duct smoke detector isI wanna know what size duct work works with a 3 ton unit. Contractor's Assistant: I understand you're looking for information on the size of duct work that works with a 3 ton unit. Is this for a residential or commercial HVAC system? ... I suggest return be 25% larger than supply.20 X 14. It was my pleasure working with you today. Please ...

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This article will guide you in determining the appropriate size for the supply duct of a 5 ton unit. Factors to Consider. Before selecting the size of the supply duct, you need to take into account various factors, including: The BTU (British Thermal Units) rating of the unit; The length of the duct run; Any bends, elbows, or turns in the duct ...The Main power is supplied to the outdoor unit. The indoor unit draws its power from the outdoor unit. The system is operated by a wireless remote control (supplied). ... 3. Number of Tons.75 ton. Pack Size. 2. Returnable. 90-Day. Voltage (v) 110v. Wattage (watts) 1140. ... (3/4 Ton) Ductless (Duct Free) Mini Split Air Conditioner and Heat Pump ...A supply duct can be too big if it exceeds the capacity of the HVAC system or if it results in inefficient airflow distribution. Proper duct sizing is essential to avoid these issues. ... What size duct does a 5-ton unit need to operate properly? A 5-ton HVAC unit typically requires ductwork sized to handle around 2000-2400 CFM. The exact duct ...Square Supply Duct; Supply Tubing; Unico 1-1.5 Ton Components; Unico 2-2.5 Ton Components; ... Bosch BRB-36HWD1N1-M18 3 Ton Inverted Ducted Packaged Unit. $6,220.58; ... Bosch IDP Brochure.pdf File Size 12.07MB Downloaded: 329: Bosch specifications.pdf File Size 2.01MB Downloaded: ...

That duct size can handle twice what your asking to do . ... I currently have a 3 ton unit but am looking at upgrading to a 3.5 ton so addition can have a vent. Do I have to create a bigger intake? ... Question regarding sizing supply and return extended plenums. This is a 2 story colonial type house with a half basement. Its 1,770 square feet ...Installing a window AC unit costs between $200 and $1,300, depending on size and brand. These units work like central air conditioners, pulling in outside air, cooling it and circulating it into ...So if you go 25% bigger, I'd expect to notice much improvement in capacity & efficiency you'd certainly need more duct and register capacity. I'd bet staying 2 ton and having the duct system checked and improved would be all you need. Reply. 08-02-2013, 08:27 PM #7. kangaroogod.3.3 Ducted Split System - High Static Pressure 42K - 48K - 60K 3 1 : Supply Air To Indoor Unit 2 : Return Air From Indoor Unit 3 : Air filter (s) 4 : Electrical Box 5 : Condensate Drain Hose 6 : Inter-connecting refrigerant piping lines and electrical cables between outdoor and indoor units. 7 : Wired Room Controller ( Standard )3.0 Ton AC - Heat Pump. 855-382-8110. Home - About - SiteMap - Contact . Search BY BTU Capacity: 9,000: 12,000: 18,000: ... 3: Supply Duct: 18" x 10 5/16" Connection type: Sweat: Pipe Size (liquid - gas): ... Once a non-defective unit is installed by a HVAC company, chances of anything going wrong are very slim and almost all contractors will ...A common rule of thumb for HVAC duct sizing is to have around 400 CFM per ton of cooling capacity. So, for a 5-ton unit, you would aim for 2000 CFM. How many CFM does a 3-inch pipe use?HVAC Unit Sizing Chart with CFM per ton and starting supply and return size Notice that the CFM values in the above table are listed as a range. Whether your system flows at the minimum or the maximum of this range is dependent on the system’s friction loss as well as the equipment chosen.Hi, I have a 5 ton a/c unit cooling just shy of 2,000 sq ft. My air return is built into a sealed box positioned between 2 walls at the bottom of the second floor. ... 2 to 3 feet of horizontal duct, and another 90 degree elbow to connect the duct to the unit. Thanks for your help! ... I am trying to figure out what size supply trunks, return ...

If the return duct size is too small, it will restrict air flow and decrease efficiency. If the return duct size is too large, it will cause increased energy costs due to wasted airflow. A good rule of thumb for sizing a return duct for a 4 ton unit is to use a 6″ diameter pipe for every 1000 CFM of airflow.

Heat strip would be sized to 80% of 27,230 = 21,790 BTU/HR = 6 kW per ACCA Manual J practice. Two 3 kW heat strips would be practical to handle the Aux Heat down to 10'F with a 2-ton 10 HSPF rated heat pump. Auxiliary heat (one 3 kW strip operating) would typically be necessary at > 22'F and < 34'F.Unless you select a square grille (such as a Cube Core with an Eggcrate design ), the size of the hole in the wall will not be the size of the grille you need. This is because a frame’s outer dimension adds roughly 2 inches to the overall size. For example, a 14x12 inch supply or return air grille with 16x14 inch dimensions will require a ...We would like to show you a description here but the site won’t allow us.R410A, the 7/8" suction line will lose 936 BTUs of capacity per 100 foot. So at 35', it will lose 328BTUs of capacity. R22, the 7/8" suction line lost 2105 BTUs of capacity per 100 foot. So at 35', it lost 737BTUs of capacity. Using 7/8" on the R410A Goodman 4 ton, will lose you a tad of its efficiency.Small to medium-sized enterprises contribute 60% of Indonesia’s gross domestic product. But companies in the D2C space still struggle to compete against bigger brands. Praktis want...By using this equation, we can determine the size of the return grille we need for 400 CFM airflow like this: Grille Area (400 CFM) = 400 CFM ÷ 500 FPM ÷ 0.7 × 144 = 164 Sq In. That means we will need a grill with at least 164 square inches of area to accommodate for a 400 CFM airflow. 10×10 grille, for example, has a 100 sq in area; it ...Feb 19, 2024 · We have included charts for most of the popular standard air duct sizes. These include: Round flex duct: 5 inch – 20 inch. Metal round pipe: 5 inch – 20 inch. 4 inch rectangular duct: 6 inch – 24 inch diameter. 6 inch rectangular duct: 4 inch – 30 inch diameter. 8 inch rectangular duct: 4 inch – 36 inch diameter. 1. Yes, my "Ductulator" says a 12" diameter duct (with insulation on the exterior of the duct) is a little small, but barely adequate for a 2 ton unit. If I was sizing it I'd use a 14" diameter with a friction loss of .09 per 100 feet of duct on the SUPPLY side and .07 on the RETURN side. However, your 12" duct will make the air ...QUICK-GUIDE. Select the duct material from the drop-down list (most duct sizing tools are typically based on galvanised steel ducting by default) Enter the air flowrate in cubic feet per minute (CFM) Enter an internal duct size in inches (this must be limited to a maximum aspect ratio of 5:1 for the results to be valid) The resulting velocity ...

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As far as the air goes. a 4 ton unit on medium is probably putting out 1400 to 1500 depending on yuor duct sizing. You need to size the bypass for the Total unit airflow, minus the smallest zone. So if your small 10" zone is around 300CFM. Then its unit T- Small zone= 1400-300=1100. You're probably somewhere in that neighborhood.The following duct sizes are based on a fraction drop of .10 inches per 100 feet of lineal duct. This "Equal-Friction" method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Larger volumes or higher static pressures should be dealt with on an individual job basis.I looked at Goodman site and they recommend a larger suction line (1 1/8"). But their TP-107 long line set application for R-410A for a 4 ton unit shows suction line values at 3/4", 7/8", and 1 1/8". My interpretation from this table is a 3/4" suction could be used but you may lose 1% capacity of the system and the same with 7/8" line for 50 ...As the summer months approach, many homeowners find themselves in need of an air conditioning system that can keep their living spaces cool and comfortable. One crucial aspect of e...A plenum is a distribution box attached to the supply outlet of the air handling unit. And the purpose of plenum box is to distribute the cooled or heated air to several spaces. It is also used to balnce the air and attenuate the sound caused by …For floor registers, they follow the same rules as return grilles, where you state the dimension parallel to the louvers first. This means that floor registers will often have a smaller number first, like 4×10 or 4×12. Ceiling and some sidewall registers will usually just be described as long side first, such as a 10×6 or 12×8, but that can ...That would be a 6" duct with a 6"x6" grille or 6"x8" grille and boot for 100-120 cfm to each of 4 registers. Or a 7" duct for 160-180cfm per 6"x8" boot and register. Throw and velocity make a big difference on small right sized systems. The registers Can't Be stamped cheap registers.What size of return duct do I need for a 3Ton HVAC air-handler. Answered in 4 minutes by: HVAC Technician: HVAC Guru. Hello, Typically a 16X20 would be fairly standard for most applications on a 3 ton unit. However if you want superior air flow I would highly suggest putting in a 20X20 as that gives you far better airflow hands down. ….

3 Bottom panel: 2 units 2 4 1. Control box 2. Fan casing 3. Fan 4. Motor ... SIZE (H x W x D mm) 120 x 120 x 18 WEIGHT ( g ) 160 CABLE LENGTH ( m ) 10 ... DUCT TYPE ARGA18-25FMTA DUCT TYPE ARGA18-25FMTA 3. SPECIFICATIONS NOTES : • Specifications are based on the following conditions:What size ductwork do I need for a 3-ton unit? 1 ton of cooling is equal to 400 CFM approximately. Hence, the airflow of a 3-ton heat pump is roughly 1200 CFM (400 x 3).Using the chart, you'll see that for a 12" round flex duct, maximum CFM is 480 CFM or 500 CFM depending on the friction rate. Duct size for 115 CFM. Find the CFM closest to 115 in the table above. It will be found in different columns depending on the friction rate. If there isn't an exact match, go up to the duct size.My 19yo AC (3.5 ton Trane) finally bit the dust and doing a complete system replacement though will likely leave most duct work. This unit serves our upstairs (about 2000 sq ft). A 2.5 ton serves our downstairs (about 1300 sq ft). Central NC. House has no shade and gets a lot of sun (dark roof, dark brick) and the attic naturally gets extremely ...Because the SDHV main supply plenum is ¼ the size of a similarly sized large duct system, 12 tons of SDHV can fit in the same physical space as 3 tons of a conventional AC system. Supply duct or tubing — SDHV systems use flexible supply tubing with a 4-inch OD and a 2-inch ID core for air delivery. These connect to the main plenum and weave ...duCt Size 01-510-16 01-515-16 47 5/8 23 5/8 13 1/2 21 45 22 1/2 11 1/4 10 1/2 16 RD 01-510-18 ... • Units are fully insulated (both supply and return). ... SUppLy DUCT ThROUGh RETURn TRAnSITIOn (15 TOn AnD LARGER) DOUBLE DEFLECTIOn GRILLS BUILT In TURnInG vAnE. Typical specifications Furnish and install Ruskin Rooftop Systems “530 …With Carrier ducted systems, a wide range of outdoor air conditioners work seamlessly with innovative indoor fan coil units to create reliable solutions that are easy-to-install and service for a wide range of residential HVAC needs. 38PK/FB4. Capacity Range (Tons): 4.0 - 5.0. Efficiency Range (EER): Up to 11.85. Details.Sep 30, 2021 · September 30, 2021. Sky Heating’s HVAC Ductwork Sizing Guide. The right sized ductwork ensures your HVAC system will work efficiently. If the ducts are too small, the system will work harder and use more energy; oversized ducts will reduce air velocity, and you might not know air is venting into rooms. HVAC ductwork sizing involves using a ... What size supply duct for 3 ton unit, Infections, gallstones, and cancer can result in bile duct problems. Discover the types, causes, symptoms, and treatment of bile duct diseases. Your liver makes a digestive juice c..., Room air conditioner size for a 3-bedroom house Room Air Conditioner Size for 4-Bedroom Houses. Below are room air conditioner sizing charts for 4-bedroom houses (2000 sqft and 2400 sqft). The air conditioner sizes (BTU) are rounded to the actual common air conditioner sizes rather than just the result of the calculated cooling capacity., Jun 7, 2023 · Undersized return air ducts result in the ducts and grills being more noisy than usual and the air conditioner components becoming stressed, thus reducing the lifetime of the unit. Use our handy return air duct size calculator or charts below to help you determine the correct return air vent size for your home. , Goodman. MSRP: $2,995.00. Items 1 to 12 of 32 total. 1. 2. 3. Next. Air Conditioning Packaged Units for Sale, Rheem 3 Ton Package Unit - Budget Air Supply., Forum Rules. I currently have a 3 ton with 16 inch metal return duct work. I was told this by a contractor: 3 ton heat pumps with the new r410a refrigerant …, Gree's High Lift design allows for extended piping length, up to 262 feet total, as well as 50 feet of vertical lift from the condensing units. This allows for greater flexibility in the layout of the system. Allows up to 262 feet of pipe length. Outdoor Unit Indoor Unit Power Supply Transmission System. Energy Saving., sure sensor must be supplied by others and installed approximately 3/4 down the longest duct run. Single Zone Variable Air Volume (SZVAV) - The 70-105 ton rooftop units are available for single zone variable air volume (SZVAV) applications. Control can be used with a zone sensor or a BAS. Supply fans are controlled based on zone temperature., A 1.5-ton unit generally costs between $2,500 and $4,500 and could adequately cool 750 to 900 square feet of space. The table below shows the typical price for various unit sizes. Unit Size (Tons), A rectangular 6×6-inch duct has an airflow of 110 CFM. Bigger 6×12-inch ducts can handle 270 CFM airflow. The bigger the crosssection of ducts, the bigger CFM; that’s pretty obvious. The smallest 6×4 ducts can handle 60 CFM airflow. The biggest 42×12 ducts with 504 sq inch crosssection can handle 3000+ CFM airflow., It has a 2 ton Skymark HVAC unit that produces 750 CFM for heat and 800 CFM for A/C. The unit is located in a bedroom closet. There are 2 supplies coming off the HVAC unit supply plenum: - 16 x 6 rectangular sheet metal duct feeding the bedroom. - 12 x 6 rectangular duct feeding the living room (and remainder of apt), fed by 9" flex duct …, Size of Your Home. Generally, the size of your home determines how many vents you will need per room. If your room is larger than 100 square feet, you will need more than one vent (at least two) to really get adequate airflow to the room. If the room is smaller, you only need one. Our favorite tip: Divide the number of air vents that you have ..., Choose the wire size based on the minimum ampacity. 12 AWG wire has 20A ampacity; it's too small. 10 AWG wire has 25A ampacity (above the required minimum of 20.45A). That means that we need to use a 10 AWG wire (or larger) for a 3-ton air conditioner. Most air conditioners with up to 5-ton capacity require from 18 AWG to 10 AWG wire sizes., The cfm should be matched to the condensing unit. 1200 cfm max for your 3 ton unit. Even at 1600 cfm your temp rise should still be up around 17 deg, so either the system isn't performing well or you're taking inaccurate measurements. 1350 is fine for a heat pump, in heating mode. 1600 a bit too much., ROUND DUCT SIZE, THESE SIZES WILL INSURE A QUIET AIR SPEED OF ... •10% rule ( after 15' 0f supply run you lose 10% for every additional 5') ... •3 ton x 5 gallons = 15 gallons minimum buffer tank . Copper Pipe Pressure Losses (Type L) Pressure Drop, Ft water/100Ft, Multiply it by 144 to get the grille size in square inches and choose your preferred grille size based on that. For instance, 400 cfm ÷ 350 x 144 = 164.57 sq.in. So, the possible grille sizes are 20×8 (160 sq.in), 16×10 (160 sq.in) or 14×12 (168 sq.in) depending on your duct size. The above way is based on the grille sizing formula which:, What size return duct do I need for a 3-ton unit? A 3-ton unit uses approximately 1200 CFMs or approximately 400 CFMs per ton. The lowest you should …, When added to an existing forced-air heating system, central air for a 2,000-square-foot home costs $3,500 to $4,000 and can be done by two technicians in two to three days, often with little or no change to the ducting. For a house that needs ducts, the costs and work time double., Built-in drain pump allows for installation of slim duct unit in smaller spaces than traditional units. Smart System: Auto Mode. When the system is initially turned on, the fan speed is HIGH to reach the set temperature as quickly as possible. The fan speed will automatically adjust downward as the room begins to reach the set temperature., The smallest return air grille is usually starts at 4 inches by 4 inches. So, the next corresponding return air grille size includes 4×6, 6×6, 6×4, 8×6, 4×8 and so on. The largest return air grille is typically stops at 48 inches by 24 inches. Here are some examples of a standard return air grille: 4×4. 6×6., 3. Q: How many sizes of units do you have? A: Currently, there are 4 systems available; a 1218 model with a nominal capacity of 1 to 1.5 tons (3.5 to 5.3 kW) system, a 2430 model with a nominal capacity of 2 to 2.5 tons ... The system requires only two types of duct – the main plenum and the supply tubing. The supply tubing is a 2 …, Here's an example with the new ASHRAE duct size calculator. Our friction rate is 0.073 iwc/100′. ... 400 cfm at 0.073 iwc/100′ corresponds to a velocity of about 725 feet per minute (fpm). That's fine for supply ducts. To move 400 cfm on the return side in this duct system, we'd need to move to a larger duct. ... This would keep sound ..., Calculating CFM requires knowing the output of the HVAC system in tons. This number is multiplied by 400 and then divided by the home's total square footage. The result is the CFM. HVAC professionals determine the CFM for every room in the house. Friction loss rate of ducts., By using this equation, we can determine the size of the return grille we need for 400 CFM airflow like this: Grille Area (400 CFM) = 400 CFM ÷ 500 FPM ÷ 0.7 × 144 = 164 Sq In. That means we will need a grill with at least 164 square inches of area to accommodate for a 400 CFM airflow. 10×10 grille, for example, has a 100 sq in area; it ..., Feb 27, 2017 · 2 ton does not give you 1000cfm. 2 ton gives you 800 cfm. Also, you need to tell us if you're measuring your return duct by inside measurements or outside measurements. Yes, I understand that 2 ton gives me 800 cfm. The picture just shows that my 12x16 gives me 1000cfm (sufficient for my units' return, maybe). , To know the size of the return air duct for your four-ton unit, use this formula: For a rectangular duct, multiply the size of the AC by 144 square inches, 4×144=576. The square root of 576 is 24, so the size of a rectangular return duct. For a round duct, you will need the CFM rating, which is 400 per ton. Multiply 4×400., Supply Duct Opening Return Duct 4.0 1.75 9.75 24.75 16.0 Condensing ... Heating Output (Btuh) CFM Range Heating Rise Range (°F) Cooling Output (Btuh) Blower Size Motor (HP) X24K080XB 80,000 64,800 1100 - 1350 35-65 24,000 10 X 10 1/2 52,000 42,120 750 - 1050 X36K100XB ... 2 TON UNITS 3 TON UNITS 4 - 5 TON UNITS BLOWER SELECTOR SETTING ..., Ventilation duct price list for supply air duct and exhaust air duct including spiral duct, flexible duct and rectangular duct. ... UNIT MATERIAL PHP / METER; 1: Rectangular Duct: W=150mm, H=100mm: 1 meter: GI: 615.98 : 2: ... Nylon tube or polyamide tube price list from size […] Pneumatic Silencer Price List. Pneumatic muffler or pneumatic ..., Here are two examples: a right and a wrong way to design this ductwork. The first (right) way uses 6" diameter pipe run all the way to the planer from the cyclone. This design will work and be able to deliver the desired 800 CFM. The second (wrong) way uses all 4" pipe run from the cyclone to the planer. This design will not get the desired ..., Hello! I am the owner for 9 months of a 3,500 sqft one-story home over full basement in central NJ. It was built 25 years ago and is of average++ construction. The heating and A/C is provided by 2 identical natural-gas, forced air furnaces and 2 X 3-ton A/C. All ducts are in the basement. The furnaces and A/C are original, so about 25 years old, Carrier units, 100K BTUH furnaces that have a ..., Size of unit for a proposed installation should be based ... 1½ Ton 24 - 2 Ton 30 - 2½ Ton 36 - 3 Ton 42 - 3½ Ton 48 - 4 Ton 60 - 5 Ton A - Air Conditioner ... the supply air duct flange and the first 3 feet of supply air duct require a minimum of 1/4 inch clearance to combustible material for model series W30, W36, W42, W48 and W60. ..., For a 3-ton unit, we use 18 inch round returns ducts or 20×12, 22×10, and 30×8 rectangular returns ducts. These ducts can facilitate at least 1,200 CFM airflow. For a 3.5-ton unit, …, Furthermore, without a return air duct in each major room, the supply duct air has to "push" all of the air in the room out of the way as it makes its way towards you. The return air ducts help pull the air as it is being pushed. An HVAC return air can be in the floor, but they work much better on walls up about 7 feet., What size return air grill for a 48000 BTU heating system? 48,000 btus is equal to 4 tons of air flow, 12,000 btus per ton. You need 144 sq in per ton.