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Product specification for my new Trane XV-80 furnace mentions something about its filter - its recommended type is "High Velocity".

What is that? Is it related to MERV or MPR? If yes, what values of MERV/MPR make a filter "High Velocity" one?

  • High velocity means the filter can handle high flow rates. the higher the MERV number the more expensive they tend to be. A minimum MERV # 0f 4 is needed to protect the furnace a good value to help indoor air quality is 8-9 this blocks more with the max @16. The higher the value the larger surface area will be needed so they start getting thicker with larger pleated folds. Hope this helps. – Ed Beal Oct 30 '16 at 14:42
  • @EdBeal - I generally get the idea. The better the filtering, the slower the air flow, so the surface must be larger to compensate the loss of the air speed - right? My question was about numerical values... When I go to a store to buy a new filter I don't see a shelf with "high velocity" ones - there are only MERV's etc – HEKTO Oct 31 '16 at 18:54
  • MERV, MPR is the level of contaminants that the filter removes same thing from different standards the don't go below MERV of 4 because this can allow dust to pass through the filter and damage the furnace. I haven't installed many furnaces but the ones I did came with the recommended type based on the duct size. I only posted as a comment because "High Velocity" is manufacturer & duct size dependent what may be considered a high velocity in your house would be a low velocity in my home the intake ducts I installed are over 25% larger than needed so I could use higher MERV value (12) . – Ed Beal Oct 31 '16 at 19:28
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High velocity filters as it applies to Trane/American Standard filters are the black plastic filters that come with the furnace. They are designed to have very little resistance and can fit in the bottom of the furnace. The problem is they don"t filter that much. The common problem that virtually all modern furnaces have is that they make the furnaces so small that they can not fit a proper size filter in the furnace itself. A 3 ton air conditioner for instance, requires 1200 cubic feet of air per minute to operate properly. Assuming a relatively good MERV 10 filter, the filter would need to be at least 20" X 30" X 1" or 14" X 25" X 2". Those are not going to fit in many furnaces. The installer would have to install an additional filter rack to fit these filters (which I would recommend)if you want proper air flow and good filtration. In order to have as much air flow in the limited space available the manufacturers specify high velocity filters that don't filter very well but it is better than starving the furnace for air. A dirty high velocity filter will still flow more air than a brand new high MERV filter.

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I would like to clarify perhaps the original questioner's issue which was not answered: The question seems to be what specification(s) do I need (look for) in an after-market filter that meets Trane's requirement for "high velocity air-flow?"

As previously stated by one response, MIRV only rates "cleaning" capacity and that is not an air-flow specification. Unfortunately, Trane does not define what range of air flow is necessary in order to meet its "high velocity" requirement, which leaves the filter manufacturers unable to provide the information. If high velocity is a meaningful term associated with the operation of the system, then the owner needs to be told exactly what that specification relates to as to system's air flow capacity requirements!

If the homeowner purchases an after market filter, it will likely decrease system efficiency to varying degrees, but worst, may give manufacturer/dealer opportunity to disclaim warranty.

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