changing return and supply register grilles

[turfgrass]

I'm about to have my hardwood floors refinished and possible wainscoting installed. The current registers are made of metal and cover supply/return air cutouts in the floors. Those floor openings are also close to the wall so, the registers form a right angle to the baseboard. I'm not sure of the style register, but they are wedge shaped looking.

Anyway, I want the wood floor installers to replace the registers with either the flush mount or surface mount style grilles. They come in slotted for supply and egg crate style for return air. Both are made of wood to match the white oak hardwood floor species and stain. My question is on sizing these new grilles correctly. The flooring guys and grille manufactures are independent. I just need select and order the correct grilles for the project.

I know that the supply branch runs are all 6" round metal pipe and the register boot that ends at the floor opening look like narrow 10 or 12" slits. Guessing because away on business. Based on those specs what would be the correct size grille be to avoid noise, but not disrupt the correct flow of air? In addition to rectangular dimensions, the manufacture also provides the estimated area of free air space. I could select from a chart of manufactured grilles if giving a size or estimate of free air space. I'm guessing this change in grille style will be restrictive to air flow and increased noise. If there is a better fitted rectangular register boot to match the 6" round branch, I will let the installer know so, they can make a larger subfloor cut out to fit the boot.

For the return side, I want to use the egg crate style grilles. They seems to be popular in my area and offer a higher amount of free air space. The sheet metal panned floor joist make up the return air branch from the ducts. The floor joists are 2x9 construction, but the staggering of joist over the main support beam are only 7" wide, or a 9x7 return joist channel. Not knowing anything about how many cfm can pass through a 9x7 area, what would be a suggested egg crate grille size or subfloor cutout? I can also get an estimated free air space by the manufacture. The dimensions all have to be rectangular to fit the floor joists. The current floor openings are to small to fit this style grille. I think they are a couple inches wide by maybe 15" long. Any help is appreciated. Thanks in advance.

[motoguy128]

All of the flush wood floor registers I'm seen appear to have thick fins and what I would generally consider very poor throw and more restrictive. I'd go with some good quality steel registers. The ones I've seen are cheaper that the flush wood ones.

I like the Hart & Cooley 210 and 265 floor registers and return grills. Very rugged and durable, great throw and low restriction.

I actually put these in the downstairs of my home to increase airflow without having to cut in more registers and do major ductwork surgery.

[cartercrew]

A quick search reveals that a Hart Cooley 406 register has 32 square inches of free area, while a wood register from http://www.volko.com/oakbasevents.htm has only 24. Simple math (and it is not quite this simple) shows that the wood register will only flow 3/4 the air of the metal grill. This is means that if the duct system and registers were appropriately sized, they will now be too small. If it is large enough to handle the restriction, the air balance and flow will most likely have to be adjusted. While more decorative for sure, the duct system and home comfort could be compromised. Have your HVAC pro evaluate the system to be sure.

[turfgrass]

Some of the supply register boots are in a room with tongue and groove pine boards. These boards extend over the supply floor cutout that is already narrow. I thought that wasnt right whether a baseboard grille or flush mount grille is used. Is there rectangular register boot that matches to a 6" round branch. For example, the duct chart states that a 6" round can deliver 85 cfm. What would be an acceptable register boot size to deliver good air flow and low noise. I'll have to find a baseboard grille since members on this site are recommending them over flush mounts.