New Return Drop, Filter Cabinet & Static Pressure
Well.....The new return drop has been installed.....along with a horrizontal media cabinet.
First, the installation. I was with my duct pro the entire time and he used me as a pair of extra hands. Recall that he is in commercial HVAC now and is doing this as a side job since we both work at the same company (although he is still charging me $$).
The first thing he noticed when he took the old return drop off were additional flaws from the original installation. The bottom of the return EL boot was not sealed and the contraption that was suppose to hold the factory filter in place was mis-aligned allowing unfilted air to go around. Before installing the new El-boot he put a hefty bead of silicone in place acknowledging it is very difficult to seal after installing.
I have attached pictures of the before with the 24 x 10 return compared to the after with the 24x20 return. (Before anyone asks I moved the yellow Energy star Label from the side to the front of the unit (so you will only see it in the "after" pictures).
That's one big return drop. How did it improve the static pressure, if you know yet?
Oooppss....I jumped out the post after attaching pics....
The air filter I went with was GeneralAire. I researched Honeywell, Arpilaire, Air Bear, etc....and at the end of the day this unit was the best bang for the buck and it is compatible with filters from Honeywell, Air Bear, and Source1.
I did not like Aprilaire and after I saw the installation video for it, I was thrilled I did not get it (A video comes with the filter cabinet if you purchase it from the online site I bought it at and Aprilaire and Honeywell units were shown in the installation examples). I guess adding all those spacers properly aligned between each pleat and then clipping it all in to a unit that ultimately goes in the filter cabinet.....may not be to bad for the 1st time, but I could not imagine handling the dirty filter to get the spacers out and unclipping it with 6 months of filtered dust flying all over. The Generalaire 2000 is very simple I just slide it in and 6 months later slide it out directly into a trash bag.
The unit comes with a Merv 10 filter with stated pressure drop range of 0.11 at 1200 CFM, 0.14 at 1400, 0.17 at 1600, and 0.26 at 2000. My actual measured PD was 0.14 right on the nose so I must be pushing close to 1400 CFM.
Another thing, I really like the horizontal installation because it allows me to use the larger 25x 20 filter set up. If I used the vertical installation next to the furnace I would be limited to a 25x16 set up.
Now for the other reason I changed RD size....static pressure.
First I'd like to say the suction at the 2 return grilles upstairs originally could barely hold 1 paper towell ...now they can hold a magazine!!!
Just kidding, but I did try 4 paper towells with no problem. The return has obviously improved which is why I am now looking into getting larger retun grills upstairs to futher help with comfort. My current grill openings are 9.5x6 (actual hole size) and I am moving to either 14x14 or 14x20. (They are wall cavity returns panned in the basement and the available space between the studs is 14 inches)
Concerning static pressure...... although lots of readings were taken at multiple places I will focus for now on a few readings to avoid confusion.
All data obtained the same day, as this was a one day installation.
With old return drop with 1" pleated merv-8 Naturaire flanders filter in place (3 for 8 bucks at home stores).
Negative SP = 0.46, Pos= 0.52, Tot. = 0.98
For the same exact set-up with filter removed, Neg = 0.28, pos = 0.62, total = 0.87
With the new return drop with 5" pleated Merv-10 Generalaire filter.
Negative SP=0.35, Pos= 0.59, Total = 0.94
For the same exact set-up with filter removed, Neg = 0.19, pos = 0.63, total = 0.82
Our interpretation of the data is that I was "return air starved" so the supply could not reach it's full potential. The only apple to apple comparison here is with no filter. The old neg pressure was 0.28 and the new is 0.19. That is the difference attributable to the new RD.
One benefit is I can now increase my return air grills up stairs and address my upstairs comfort problem that way rather than balancing dampers and further increasing my positive static pressure.
As far as positive static goes, Udarrel mentioned it earlear that I would have to re-size all the way to the supply registers. I have a question on this. I looked inside my supply grills and they only have a 3 inch sqaure opening. Would'nt that cause my SP to be high? See pic attached
That can be a major restriction.
Is connector under the supply box bigger.
If so, if the box opening is made bigger, it will make a difference also.
A 5 inch pipe has 19.6 sq in of area.
Does the new elbow have vanes,as the inside radius is way to small to be low static.?
The supply box/boot needs to be caulked,up to 15% duct leakage at that point,leaks to behind the drywall,when the grille is in place.
From your pics,supply plenum needs to be reworked,with you guessed it,turning vanes.
Remove the return grilles you plan to enlarge and test the static,to see the potential for enlarging them.
Last edited by dash; 07-27-2008 at 07:06 PM.
If I remove the grill why would I expect a change as the 9.5 x 6 inch opening is still the same size? Recall these are walled in ducts and if a hole is cut 14x14 that will be the actual new size of the end of "duct" opening. My main reason for larger grills is more return air upstairs to help bring temperature down.
Originally Posted by dash
[QUOTE=key1cc;1941117]If I remove the grill why would I expect a change as the 9.5 x 6 inch opening is still the same size?/QUOTE]
The sheet metal of the grill covers up to 50% of that 9.5 x 6 inches, plus the vanes on it cause turbulence and resistance.
When the old Return drop was being removed an ~ 18 inch section was cut out of the middle leaving only the old el-boot and ~ 2ft of attached duct (to make the removal easier). At that point we decided to take static pressure. When the new return drop was installed, static pressure was taken again after the new el-boot and ~ 2ft of duct was installed to have a direct comparison of the the effect of the EL's. Both measurements were made without filters
Originally Posted by dash
When the old El was in place neg static was 0.12
When the new El-Duct was in place neg static was 0.07.
Both taken with basement return air being sucked into the wide open return boot. (The boot was connected to furnace but the other end was left unconnected for this measurement.)
No vanes but the new one has an inside radius curvature.
Fortunately, this project has become more fun for me than aggravating. I think one reason is because it is costing me very little $$. The duct pro lives nearby and he is enjoying this as he wants to use before and after pics to use on his resume to get more side (higher paying residential jobs). The return drop cost was actually not much more than the GeneralAir filter kit (which was less than 1/2 the cost of the Aprilaire filter kit).
I believe the installer wants this undertaking to be successful so he sold the RD cheap.
Sorry ,typo,should small be instead of same,regarding the elbow.
Originally Posted by key1cc
The inside radius would need to be half the duct width to be effective.As it is it's not much better than a square elbow with no vanes.
A sq. elbow with vanes fits in a smaller area then a properly made radius elbow ,with the proper inside radius.
Most all the pics of jobs on this site that have radius elbows,are the same or worse then yours.
On removing the grilles,the pressure drop reduction of doubling the grille size will be around the same as removing the existing grille,it is also the same as the highest PD of the grilles not times three.I would do it,but vanes in that elbow would have been a better investment.As someone said earlier,it's the duct size(or in this case bad fitting,no vanes),more then the grille size.