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Originally Posted by mark beiser

IF you decide to do a typical 1 or 2 bulb UVC system, have it irradiating the coil, otherwise it does little to no good.
All of the materials within about 3 feet of it need to be rated for UVC exposure too.

Ironically, though all materials within 3' need to be UV rated, UV light really only has a positive affect within 6-8" of the bulb and then only on substances that are exposed for a minimal amount of time. Air blowing across an UV light gets no positive results from that light.

Even pros have differing opinions. The main issue is keep the filter clean. I have seen both scenarios where the inside of the units were still clean after 10 years. I have also seen both scenarios where the units were dirty after just a few years.

Originally Posted by seanhoang

I've been looking into this option - replacing my 1" with a 4" media filter at the return grille.

Would this option at the return grille gives the same performance as the one at the blower? If not, what is the differences?

Also, I was thinking about adding a UV light behind the media filter. Is it really worth it?

Thanks in advance pros.

Filter(s) at the return air grille(s). The velocity will be lower there and dust won't accumulate in the return duct(s)/box/chase/whatever. Seal the return air path to prevent leakage or install a low resistance (cheap) secondary filter at the unit. Use your best judgment. Do some research on UV lights. They don't treat the air they treat the evaporator coil and can cause damage if not installed correctly.

Originally Posted by seanhoang

Also, I was thinking about adding a UV light behind the media filter. Is it really worth it?

IF you decide to do a typical 1 or 2 bulb UVC system, have it irradiating the coil, otherwise it does little to no good.
All of the materials within about 3 feet of it need to be rated for UVC exposure too.

Originally Posted by RoBoTeq

For total SP, yes, but not for velocity across the face of the filter. We have to also account for filter grills having 40% of the open surface area blocked by louvers.

Add in the ability for unfiltered air to infiltrate the return ducting between the filter grill and the blower assembly, and there are more reasons to put the filter close to the blower than there are reasons to have the convenience of a filter grill.

Velocities suggested for a one inch media are considerably more tolerable to higher values than the four inch pleats. An EAC next to a furnace does not make sense when the F.P.M. is double if not tripple the recommended statistic derived from an UL standard. Slow it down for better filtration efficiency.

Total not totatal... Forgive the typo.

Nobody that I thumbed through has pointed out the fact of face velocity per area of the duct. Every installation is unique with their own idiosyncratic developments. Mastic the return air duct weather it's part of a municipal code or not, and if your using it in the return add up the free surface of the grille versus your cubic feet for the totatal equivalent length of duct. In many cases a higher M.E.R.V. Value is an option of cost but efficiency can be improved by capturing the correct velocity through engineering an oversized rack even with a one inch fiber constructed media..

Originally Posted by 54regcab

I'm a bit confused on how the location of the filter affects the total static pressure drop. If the filter has a drop of .2" @ 1400CFM and the return duct has a drop of .1" @ 1400CFM doesn't that equal .3" no matter if the return duct or filter comes first?

For total SP, yes, but not for velocity across the face of the filter. We have to also account for filter grills having 40% of the open surface area blocked by louvers.

Add in the ability for unfiltered air to infiltrate the return ducting between the filter grill and the blower assembly, and there are more reasons to put the filter close to the blower than there are reasons to have the convenience of a filter grill.

I'm a bit confused on how the location of the filter affects the total static pressure drop. If the filter has a drop of .2" @ 1400CFM and the return duct has a drop of .1" @ 1400CFM doesn't that equal .3" no matter if the return duct or filter comes first?

Originally Posted by seanhoang

The reason for this thread in the first place was really to see if it is worth the trip to just to go with a replacement media filter at the grille or spend the money to go with the media filter cabinet. Is performance, as well as saving monthly cost, worth doing it?

By the way pros, I have 2.5ton units, 20x25x1 filter, 1750sqft house, 1 story.

While I have you on the topic of return grille. How does one determine if 20x25x1 is right for a 2.5ton unit? It is confusing the heck out of me when I read many threads different sizes for different unit and some home have 2 or 3 returns?

A 20 X 25 4" pleated filter at the air handler is a little more than is needed, which is really good. That same filter located at a filter grill is just about what you'd need to account for ducting static pressure and the decrease of free area space due to the grill.

Originally Posted by RoBoTeq

You want to have the filter as close to the blower as possible. With the filter located at the grill, the static pressure in the return duct now has to include the pressure drop across the filter.

Lower velocity across the filter increases the filter's efficiency.

The reason for this thread in the first place was really to see if it is worth the trip to just to go with a replacement media filter at the grille or spend the money to go with the media filter cabinet. Is performance, as well as saving monthly cost, worth doing it?

By the way pros, I have 2.5ton units, 20x25x1 filter, 1750sqft house, 1 story.

While I have you on the topic of return grille. How does one determine if 20x25x1 is right for a 2.5ton unit? It is confusing the heck out of me when I read many threads different sizes for different unit and some home have 2 or 3 returns?

You want to have the filter as close to the blower as possible. With the filter located at the grill, the static pressure in the return duct now has to include the pressure drop across the filter.

Lower velocity across the filter increases the filter's efficiency.

Originally Posted by seanhoang

How would that affect performances? Does slower velocity equates to better cooling? Better humidity reduction? Better noise reduction? Lower electricity costs?

Also, would a larger media filter makes much of a difference, such as 4" vs. 5"? Again, thanks.

Lower velocity will not affect cooling ability, that is affected by volume of air. The slower velocities allows the filter to hold particles better.

the 4" media filter at the air handler is the way to go. What size is your unit? Sizing is important to determine which filter to use. Common sizes are the 16x25 and 20x25. On the 4 and 5-tons the static will increase so with that said what size is your return air duct and existing grill opening?

As you increase the static you will affect the effeciency and capacity of your cooling system. Most filters are 4", but some that are 5" are higher MERV filters like Lennox's MERV16. I would keep it simple, like the Honeywell F100 or 200 (4" filters - MERV 10-12)

UV-lights, becarefull they can burn the media filter. Why do you want a UV-light?

Originally Posted by rglasgow

Agree with t527ed. Also look at where you will have the largest square inches of filter size. The larger the area,the slower the velocity.

How would that affect performances? Does slower velocity equates to better cooling? Better humidity reduction? Better noise reduction? Lower electricity costs?

Also, would a larger media filter makes much of a difference, such as 4" vs. 5"? Again, thanks.

Agree with t527ed. Also look at where you will have the largest square inches of filter size. The larger the area,the slower the velocity.

unless you can guarantee the return ducting is 100% sealed i would rather have it at the unit.
with it at the grill any leaks in the return duct will allow dirt into the unit.

I just bent back the side tabs on my 20x20x1 filter grills so the 4" media would fit. Works great, static is low enough that filters never get sucked into to the return. I can buy the 4" media at the supply house for about the same price at the 1" filters at the big box store in the fancy retail packaging. 4" media filters are awesome, well worth it IMHO. The UV light, I'm not sold on those...

How annoying is it at the grille? Is it pretty noticeable? And did you say "increase" static pressure at the box? Don't we want to keep static pressure lower though? Please advise...

Originally Posted by seanhoang

I've been looking into this option - replacing my 1" with a 4" media filter at the return grille.

Would this option at the return grille gives the same performance as the one at the blower? If not, what is the differences?

Also, I was thinking about adding a UV light behind the media filter. Is it really worth it?

Thanks in advance pros.

A media filter is great no doubt about it yet in my experience on any install done i've always placed them closer to the unit in either a pre-cut box or just a 4 inch opening on the sheet metal. The upside to placing it near the unit is that it wont make as much noise, it will just increase the static of the system. By placing it at a return grille its going to have a long run back to the unit and it will be much louder, you will most likely hear the suction of air. If you do install it I would definitely install it closer to the unit and just remember to remove the one in the filter grille assemble. I would really only replace it if someone has asthma, keep in mind the x4 filters are a little bit more costly. As for the light it depends your use, will it be for coil treatment or used as an air cleaner. The lights themselves are pricey as well as the replacement bulbs. If your using it for coil treatment i would hard wire it to run all the time. If your going to use it to treat the air I would wire it in series with a sail switch so when the blower comes on the light comes on. Check out Honeywell's website for the light depending on the size of the duct and then the choice of placing it in either the supply or return is upto you. Good luck