We have a handyman who always puts in a furnace filter that is twice as large as the hole for it. He bends it in half like a puptent, with the top ridge facing into the downdraft. He says it’s simple math, that the filter will take twice as long to clog up.
But I wonder, is this going to block the flow?
Let’s say it normally would take 1 month to clog a singe filter.
With this double filter it seems less clogged. because if you took it out and held it spread out to the light, half the light would come through.
But if you keep it in the tented position, it lookes blocked and there is as much dust between the top of the pipe and the bottom as a regular clogged filter, so shouldn’t it be blocking the flow?
It doesn’t seem like it would block the flow, but actually aid it as there is more ‘space’ for the air (not light) to get through. But I have never seen a furnace set up to accept a pup - tent filter. I would just be concerned that air is not getting around it.
It might surprise you to know that the furnace filter is there to protect the FURNACE and not to fight for your oveall comfort.
If air is bypassing that “jury-rigged” filter it can admit undesirable materials to accumulate in the plenum and shorten it’s life by creating"hot spots".
These will inevitably shorten the life of the heat plenum.
Stick to the size and type of filter recommended in your manual.
You and your purse will be glad you did.
EZ
As long as all the air entering your furnace return passes through the filter, all is well. Having twice the surface area will give you more time between filter changes. This is the rationale behind pleated filters. It also (as pointed out by kanicbird) reduces blockage by allowing a larger surface area for air to flow through. The important issue is that no air is leaking around the edges of the filter. If your furnace is part of a central A/C system which includes a cooling section, the filter’s most important role is protect your evaporator coil. Dust and dirt building up there can have serious negative consequences for your air flow, cooling efficiency and life of the A/C compressor.
These are good points-which I had forgotten to include-------But I repeat-----the filter is to protect the Unit!
This is nuts. As was stated, air with dust in it can go around the edges of the filter and get into the duct work. I would tell the handyman either he use the correct filter or to not change it and then I would do it myself. I don’t know how much your filter costs but it can’t be much of an expense.
Right. Filters can be placed in angled positions to provide a larger surface area, but the furnace has to have filter frames designed for it (and in these cases, multiple filters are used). Otherwise, air will simply bypass the filter altogether where the filter and the furnace housing do not meet and create a gap. The basic idea is sound, but the implementation needs to be considered. I doubt that a folded filter in a frame designed for a flat filter is doing what the handyman intended.
Increasing the area of an air filter has a fantastic effect of prolonging its life. The life varies as about the third or fourth power of area, not the “simple math” your service man suggests. How compressible the trapped “dust cake” is, and what the failure mode of the filter is, will help dictate this.
But, yeah, air bypassing the filter could be a real problem here.
If you have a practical way of seeing that there are no leaks - or perhaps better to say that the leaks are below, say, 1% or 3% or so of the flow - then the pup tent is a good idea. Perhaps not, otherwise.
You could make everything almost perfect if you adapted your ductwork to take larger filters in the first place, and bought huge pleated filters such as the new electret filters (which work much better when you decrease their local air velocity by increasing their area). Boy, if they offered this as an option for, say, $500 when you had the system first installed, it’d be a great choice.
This is very sound advice/information.
And I would add that I can’t think of a single configuration that wouldn’t allow air to pass ‘around’ the filter. Whether the filter “rack” or “track” is in the ductwork or built into the furnace, it is designed to accomodate a specific filter size. The purpose is to force all the air through the filter.
I service HVAC equipment and I can’t think of one incident of a [well meaning] handyman gerry rigging a filter (often the ‘handyman’ is the homeowner) where there wasn’t a poor seal around the filter.
Ditch the filter. Pick up the appropriately sized pleated filter (and a pleated filter is disigned to give you more surface area!), like a Farr 20/20 or Farr 30/30.
I would second that (other than dust control in the house) the filter is going to protect primarily the outside air conditioner. (condensor) A dirty $8 filter will destroy a $1000 compressor that is outside.
In this particular case the tented filter makes a tight fit all around. You have to squeeze the paper border just a tad to get it into the square shaft at all.
I’m thinking about the importance of the edge fit, and I see that it becomes very important when the filter is clogged, since all the air will squeeze through the cracks. But if you change a filter while there is still airflow, then the edge gap is a very small part of the equation.
Not necessarily!
When ‘air balancing’ a system, one is amazed how much air will pass through a small opening----and certainly more than pure logic and observation would dictate.
For example, in a round duct with a damper, a damper at the half point would suggest that half the air is being restricted. Not so. Further, a damper almost completely closed will pass much more air than you would imagine.
As to your situation, [forced] air will take the path of least resistance. The filter is a form of resistance, and if there is a gap around the filter track (which has no resistance) you will pass more air through that gap than simple logic and/or observation would suggest.
The point is this: the edge gap is [potentially] a large part of the equation, whether the filter is clogged or not. It’s good you have a tight fit. That’s good. Still, to the extent it is reasonably possible, all gaps around filters need to be avoided. You’d be surprised how much air will pass through a small gap.