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drewp
Furnace filter

Hi, I have a sister who's on a pretty tight budget. She has a "newer" furnace and I keep on her to change her filters routinely. Here's the issue. Her housing for the filter fits a 16x25x4" filter. These babies run about $30+ per filter (at the "box" stores). What's up with that? My unit..and most I've seen use a 1" thick filter which costs a fraction of the 4" filter. I don't see anything else really different about her unit than mine or others. What's the rational for a 4" filter? Can I change the filter housing or retrofit something to allow her to use a 1" filter? I notice that the 4" filter mentions on the package that it may only have to be changed once every 6 or 12 months. So, does it have a longer interval between changes? She has 4 kids and 2 dogs in a small townhouse. She usually requires frequent changes. Thanks for any input.

motoguy128
Re: Furnace filter

The 4" media filters are often more cost effective because you cna install a MERV 8 filter and it will last as long as 12 motnhs if you don't run the fan constantly. Comparatively a 1" pleated filter will only be good for 1-3 months.

You'll easily get 4-6 months even if you run the furnace fan constantly depending on the amount of airflow and how often you vacuum.

Ultimately with a lot of people and pets you should be vacuuming weekly. That will collect 95% or more of your dust.

The purpose of a filter is to keep dust out of the equipment and protect it, not clean the air. That's a side benefit. You don;t need more than a MERV 8. A MERV 8 will also last longer without reduced airflow than a MERV 10, 11 or 13 and is still fine enough to catch most dust, dander, pollen. A home isn't a ************** plant or a hospital ICU, you don't need to capture bacteria and ultra fine particles.... especially on a tight budget. You're health will be better improved by eating better food and having healthy lifestyles than installing a expensive air filter.

A. Spruce
Re: Furnace filter

You shouldn't have to change your filters more than twice a year, if you do, then you'd best be assessing your environment to see where the dust, dander, hair, etc. is coming from.

I can tell you that if her return air grill is at floor level that it will pull in a huge amount of dust and dirt. If the RA grill is near or in the ceiling, there will be far less. If the grill is at the floor, then I highly recommend replacing the existing grill with one that will hold a filter, then install a filter in it. This will stop more than half of the dust that is now clogging the other filters. The best part is that a grill of this nature only requires the cheaper filters. I would still go with a pleated filter rather than the mesh type because it will capture more debris.

Another thing, if dust and dirt is an issue, then I would also recommend reassessing the vacuum cleaner being used in the house. Most are poorly constructed with poor filtration, meaning that a good percentage of the dirt picked up is spewed right back into the air. Yes, you're going to pay more for a good quality vacuum cleaner, but your lungs and your environment are going to thank you for it. Finally, a good vacuum is not necessarily an expensive one.

My personal favorites are:
Dyson
Miele
LG
Oreck
Shark

drewp
Re: Furnace filter

Thanks for the input guys. I didn't think we should be shelling out $30 every 2 months or so. I did see..and like the idea of the filter on the return grill. We'll give that a try AS WELL AS check the efficiency of her vacuum cleaner. Re: the return grill filter. That shouldn't affect the return flow? (I'm supposing that it's not a really efficient (restrictive) filter AND it also should be checked regularly for buildup). Thanks again.

dj1
Re: Furnace filter

Another idea is to use washable filters: remove, rinse, dry, re-install.

A. Spruce
Re: Furnace filter
drewp wrote:

Re: the return grill filter. That shouldn't affect the return flow? (I'm supposing that it's not a really efficient (restrictive) filter AND it also should be checked regularly for buildup). Thanks again.

No, as long as the filter is kept clean, there will be little restriction. I used this method at my last house that had the return air at the floor just inside the garage door. I had a woodshop in the garage, so there was a little extra dust that came in right where the grill was. After installing a filter there, the furnace filter life significantly increased. We also ran our furnace fan almost 24/7 as it was used to circulate the air in the house in addition to any heating or cooling needs.

drewp
Re: Furnace filter

Re: the washable, reusable filters. I just "googled" them and found several options for a "washable, reusable, electrostatic filter" replacement. It looks like every couple of months or so, you spray on a "cleaner" (intake side), then rinse through the other side. Then let it dry thoroughly. This sounds a lot like what I do with my (reusable) K&N air filter in my vehicle. What do you guys think of these? Sounds like a nice concept. Money saving AND keeps excess material out of landfills, etc.

motoguy128
Re: Furnace filter

The 4" media filters also have a lot less airflow resistance. I'd lean towards sticking with that filter. I don't know about the washable filters.

But if the budget is that tight, it might be worth it. Again, you're trying to protect the equipment without restricting airflow.

dj1
Re: Furnace filter

Try the washable filter. I've been using them for years in multiple residences with no equipment failures whatsoever.

If after 1 month you find out that the filter is too dirty, wash it, add a regular filter behind it and continue to inspect it in a short time. Some of those washable filters, but not all of them, can be washed many times, just like you K & N car air filter (I have one too).

A clean filter is essential to a proper a/c-heating performance.

Fencepost
Re: Furnace filter

As previously mentioned, the 4" filter provides much less resistance to air flow than a 1" filter (because the surface area of the media is much larger). Newer, high-efficiency furnaces tend to have lower fan speeds, which means the air isn't sucked through as powerfully. A 1" filter may restrict the air flow too much for the furnace to operate a peak efficiency.

As for putting a "prefilter" at the return air vent, I think I'd use one of the mesh filters rather than a pleated one. It will trap the largest dust without restricting the airflow as much as a pleated filter would.

Any filter, no matter how coarse, will still trap some amount of fine dust because air moving across a surface creates a polarized static charge in the surface (in this case the filter media) and an opposite polarized static charge in the dust in the air. This causes the dust in the air to be attracted and stick to the filter media.

motoguy128
Re: Furnace filter
Fencepost wrote:

Newer, high-efficiency furnaces tend to have lower fan speeds, which means the air isn't sucked through as powerfully. A 1" filter may restrict the air flow too much for the furnace to operate a peak efficiency.

I thought I should make sure there isn't any misinformation or myths being spread. Many of the newer furnaces use Variable speed "ECM" motors. These motors match the airflow requirements more precisely than the older less efficient PSC motors. They can adjust to changing static pressure (airflow restrictions) and therefore maintain the roper airflow. Old furnaces might have often had their blower speed set higher than nessesary to make sure there was always adequate airflow.

That being said... technically, a high efficiency furnace will need MORE airflow. Why? Because a 95% furnace puts out more heat than a 80% furnace with the same fire rate. The maximum temp rise is typically the same, so to move the extra heat, you need more air. Example... a 60k BTU 80% furnace puts out 48kBTU BTU, and at a 50F temp rise needs 810CFM. A 95% furnace the same size puts out 57kBTU and therefore needs 1060CFM at a 50F temp rise. ON an older furnace, that an entire fan speed faster on a 4 speed PSC motor. OR put this way, if fed the same amount of air, will be at a 65F temp rise, and could begin to damage the heat exchanger.

A newer furnace might seem like it needs less airflow because those with VS fans are almost always 2 stage. SO on low stage the heat output is lower. Since most furnaces are oversized, they rarely go to high stage when maintaining temp. Actually low stage is 70% capacity, so even on a proerly sized system it won;t be in high stage very often either. why it might seem that it needs less

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