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Discussion Starter · #1 ·
Every so often I keep thinking about adding a UV lamp into the furnace. After doing some research i concluded it can be a controversial topic.


Regarding the installation location: UV lamps can be installed int eh return duct or after coils or both. Just wondering the value in return duct (ignoring mold on coils for now). ow easily does mold actually make it though a quality filter?


Do UV lamps only work to clean coils or is air actually cleaned? Wild mold pass through heat in winter?


Any products more effective than others? At the core it seems UV lights are pretty simple, it is really all about the UV light bulb?
 
user_12345a

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#3 ·
I don't think the air will be exposed to the uv light long enough to kill much.

A UV light is good for stopping mold from growing on coils, in air handlers but can damage plastic parts not made to be exposed.

You may have better luck with a high-merv media filter or something like the lennox pure-air. https://www.lennox.com/products/indoor-air-quality/air-purification/pureair
 
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#4 ·
Is this due to the virus concerns?
What is a “quality filter”? Most residential air handlers don’t have the airflow capability to use highly restrictive air filters.
Contrary to what a lot of consumers believe the air handler filter is not there to filter air within the home. It’s there to prevent dust and debris from getting into the air handler. If your using a filter that claims to stop mold spores then it’s likely having a negative impact on your air handlers performance.
 
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#6 ·
I added a custom filter at the return duct so increase the overall filtration. It is 3 inches thick and I replace it now once a year in the fall. Despite have a two-stage filtration at the furnace it has helped a great deal to filter dirt that was being sucked into the return duct from the floor of the hallway in my house.

The filter fits inside the framing for the return duct which is why I needed a custom size for it. $50 a filter but well worth the cost.
https://www.airfilterusa.com/
 
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#9 · (Edited)
I would check it immediately before your equipment suffers damage from lack of airflow. Until then take out the filters and install one of those cheap blue fiberglass filters you can see through.
Restrictive filters limit airflow. Your equipment needs air to run.
Those 3M filters sell on scare tactics. Whose to say you have mold to worry about. Most material that people consider to be mold, is nothing more then a little mildew that’s not harmful at all.
 
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#10 ·
roughneck said:
We call those 3M filters furnace killers, because they usually cause destruction of the equipment.
The furnace isn’t intended to be a whole house air filter.
What’s your static pressure drop across all these filters?
Click to expand...

That is a dumb thing to say. All the air inside a house goes throught the return ducting and then to all the vents in the house. It is the only reason that I need to replace the filters for as the air is not drawn in directly from the outdoors.

The pressure from a blocked filter is what reduces the efficiency of a furnace as less air is passing through it but this does not magically increase the load on the fan motor for the furnace. Following your "logic" a MERV furnace or AC filter that traps more particles is going to damage the unit and that would be news to professionals in the HVAC industry that my company supplies.

False statements do not become true because of the age or experience of the pretend expert. I have often found that when I talked to people with 30 years of experience that they actually had 1 year of experience that was repeated 29 more times and their "facts" were either untrue or way out of date.

I worked with one food manufacturing company that was using foil lined bags for its products and when I requested that they actually test how well they worked it was discovered that the foil lined bags let in more moisture than the non-foil bags. This was because the heat sealers for the ends of the bags were less effective with the foil dissipating the heat and the result was a bad seal and moisture was coming into the bag as a result. The company had been paying more for the foil bags over the prior 30 years and no one thought to actually test them. I have seen this lack of critical thinking my entire working life.
 
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#11 ·
Calson said:
That is a dumb thing to say. All the air inside a house goes throught the return ducting and then to all the vents in the house. It is the only reason that I need to replace the filters for as the air is not drawn in directly from the outdoors.

The pressure from a blocked filter is what reduces the efficiency of a furnace as less air is passing through it but this does not magically increase the load on the fan motor for the furnace. Following your "logic" a MERV furnace or AC filter that traps more particles is going to damage the unit and that would be news to professionals in the HVAC industry that my company supplies.

False statements do not become true because of the age or experience of the pretend expert. I have often found that when I talked to people with 30 years of experience that they actually had 1 year of experience that was repeated 29 more times and their "facts" were either untrue or way out of date.

I worked with one food manufacturing company that was using foil lined bags for its products and when I requested that they actually test how well they worked it was discovered that the foil lined bags let in more moisture than the non-foil bags. This was because the heat sealers for the ends of the bags were less effective with the foil dissipating the heat and the result was a bad seal and moisture was coming into the bag as a result. The company had been paying more for the foil bags over the prior 30 years and no one thought to actually test them. I have seen this lack of critical thinking my entire working life.
Click to expand...
It’s common knowledge that standard furnace filters are not intended to be whole house filters.
If the customer wants high levels of filtration this can be achieved via high capacity filters, such as 4”, 5” or even media filters.
High MERV filters are very restrictive, and limit airflow. Limited airflow causes equipment problems and even damage.
 
user_12345a

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#12 · (Edited)
All 1" pleated filters start off quite restrictive.

The typical 16x25x1 merv 6 or 8 is only good for up to 800-900 cfm or so, a 40 to 60k furnace or 2 to 2.5 ton a/c.

A Larger unit needs 4 or 5" filter to get decent filtration just to keep the blower and coil clean.

The high merv pleated 1" filters actually start off at a similar level of restriction to the lower ones.

The problem is, the holes in the media are very small and they plug up really fast. The pressure drop shoots through the roof as soon as there's a little dust on the media.

When really dirty, a 1" filtrete allergen filter can be almost bad as a piece of plywood in the filter slot. You can actually find a youtube video showing this. Clean, most are around 0.18 to 0.22" at 300 to 400 fpm.

Allergen 1" filters should never be used!
 
user_12345a

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#16 · (Edited)
destruct said:
Interesting. So, out of the Filtrette's the 1900 is actually the least restrictive.
Found this link:
https://www.iallergy.com/pages/compare-3m-filtrete-filters


So, what is an acceptable pressure drop for my furnace?
Click to expand...

Only when new!

The pressure drop after 2 to 4 weeks of being in there is what matters.

Pressure drop goes up dramatically as airflow does and what's acceptable depends on the rest of the duct system. Each system needs to be individually tested to see if a filter is too restrictive.

Generally 0.5" static or less for the entire system including filters and coils is optimal.
Up to 0.8" is okay if the blower still has capacity to deliver proper airflow.
 
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user_12345a

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#19 ·
what size is your furnace?

model number suggest 100k furnace -> need a large filter slot to use 1" unless it's a old furnace that's designed to run hot.
 
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D

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Discussion Starter · #20 ·
I don't know the size/capacity of furnace. The furnace is original when house was built in 1999.


BTW. are thee any low cost pressure gauges that work?
The simplest I found is this:
https://www.amazon.com/General-Media-Cleaner-Filter-Gauge/dp/B0195UXV7O
Granted it doesn't give you a number reading and doesn't have a true differential pressure measurement.
 
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