![]() Allow 2 CFM per square inch of filter grille area for appropriate functioning. ![]() Step Three to Calculate Return Air Grill Sizeĭetermine the area in square inches required for your filter grille. For example, a 40,000 BTU furnace would produce 800 CFM. 2nd Step To Calculate Return Air Grill Sizeĭivide the BTU by 50 to determine the CFM, or cubic feet per minute, that your furnace produces. Check the plate to find how many BTUs (British Thermal Units) your furnace produces. To obtain access to the service plate, open the cabinet of your furnace. Step 1 To Calculate Return Air Grill Size The return air filter grille must be properly sized for the furnace to perform properly. How to Size Return Filter Grillesīecause furnace filters should be replaced at least every 90 days, going into an attic to change the filter may be impractical. Otherwise, if feasible, utilize more than one grille. You may also look for return air grilles with a bigger free space. If you must utilize a smaller return air grille, I recommend that the face velocity not exceed 800 fpm. The more the noise, the smaller the grille. The grille may make audible noise with a greater face velocity. Using a smaller return air grille with the same type of grille will result in a greater face velocity (thus, same free area). What Happens If A Smaller Return Air Grille Is Used When measuring exterior grilles, I recommend using 50% free space because external grilles often have thin blade profiles to prevent rainfall from entering. Both grilles are suited for the HVAC unit with a capacity of 1050 CFM.Īlternatively, just match the size of the grille to the airflow (cfm) of your HVAC unit. If you don’t want to utilize a horizontal grille, you can find the 24 inches by an 18-inch grille or the 36 inches by 12-inch grille using the CFM table for vertical grilles. Using the CFM chart for horizontal grilles, the 18-inch-by-24-inch grille has a grille area of 432, which is sufficient for the HVAC unit with a capacity of 1050 CFM. This is no doubt very easy to go through. Grille Area (sq.in) = Airflow (cfm) ÷ 500 ÷ 0.7 x 144Īssume we have a 1050 CFM airflow HVAC unit, then: Using the aforementioned calculation and 500 fpm with 70% free space, we get: The following formula is used to compute the size of the return air grille:Īirflow (cfm) Face Velocity (fpm) Grille Free Area (percent) x 144 = Grille Area (sq.in) ![]() The people who need to have the option to cook for a bigger group may increase to around 400 square inches. These barbecues are generally at least 360 square inches. **Unless otherwise stated in the listing.With regards to a standard barbecue size, the vast majority who need to cook sausages and burgers go for a comparable size. Delivery is generally next day service when ordered before 1pm Monday-Thursday. Orders over £100 are delivered Free of Charge to most mainland UK addresses, and orders under £100 incur a £6.95 delivery charge to most UK addresses. The Delivery By / Estimated Delivery Date is shown under the 'Add to Bag' button. Items bought over the weekend will usually be dispatched on Monday or Tuesday. We aim to pack and dispatch all our items within 48 hours of payment (Monday to Friday)**. This item is available for either Click and Collect or Delivery.Ĭlick and Collect is from our Hitchin, Hertfordshire Shop and Warehouse, Monday-Friday 9.30am-4.00pm - just choose the Click and Collect delivery option at the checkout.ĭelivery is via Courier, and the delivery date is shown under the 'Add to Basket' button above. The Delivery By Date / Estimated Delivery Date for each product is shown beneath the 'Add To Bag' button on that products page. ![]() But FireBoard 2ĭrive/Pro models will power fan directly, no Drive Fan Control Cableĭelivery details / options for this product Power source: 12 VDC, 0.68A, 8W (not included)įlange outer dimension: 1.95 x 2.45″ (49 x 62 mm)įlange mounting hole distance: 1.32 x 2.05″ 34 x 52 mm, hole size, 3īlower does NOT include Drive Fan Control Cable. For maximum fan speed, external power is required. Specifications: Variable Speed, powered by FireBoard’s internalīattery. Includes 1 Large/XL Kamado Adapter Plate: 3.43 x 3.03″ (87 x 77mm) Includes 1 Small/Medium Kamado Adapter Plate: 2.75 x 1.97″ (70 x 50mm) Installed on many smokers using the included adapter plates. Variable Speed 20 CFM Blower used with FireBoard to maintain precise
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