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Old 03-24-2010, 10:13 AM   #136
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Ok, I have run the calculations for all the rooms and for all of the various trunks and branches. Would you mind taking a look at this and giving me your opinion. Am I close? Does it make sense?

Also,

1) How do I go about sizing the actual registers. If it matters, all of the registers in the basement and on the upper level are ceiling and all of the vents on the main level are floor.

2) I am pretty sure I am going to need a new return air drop. How do I figure out what size is necessary? It seems like a 20x10 could work well for 1080 CFM.

Thanks!
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Old 03-25-2010, 10:46 AM   #137
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Bump.
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Old 03-25-2010, 01:36 PM   #138
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Quote:
Originally Posted by stubits View Post
Ok, I have run the calculations for all the rooms and for all of the various trunks and branches. Would you mind taking a look at this and giving me your opinion. Am I close? Does it make sense?

Also,

1) How do I go about sizing the actual registers. If it matters, all of the registers in the basement and on the upper level are ceiling and all of the vents on the main level are floor.

Registers are sized/selected for the throw and or spread you need for the room/area their serving.

2) I am pretty sure I am going to need a new return air drop. How do I figure out what size is necessary? It seems like a 20x10 could work well for 1080 CFM.

It will work. But, if you intend to add a media air filter now or down the road. A 12X20 will work much better.

Thanks!
Presuming the left side is the intended new duct size. You want to stay with standard height duct. 8" high is standard.

So the 20X6 would be more like 14X8.
6X6 would be 8X8.
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Old 03-25-2010, 01:50 PM   #139
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Thanks so much... as always.

So, do they have catalogs for the registers? How do you know what the specs are?

I would love to add a media filter, but I simply don't have the room for it. It is a small-ish old home. I need the smallest return air drop that will work for my system. 20x10 is about the smallest I can get away with, isn't it?

In some cases I went with odd sized ducts because of space issues. For example, in the basement, 2" makes a lot of difference. The 20x6 is an attempt to not totally overwhelm my dining room with the hvac chase. Is it that these sizes are not readily available? Are they super expensive? Tough to work with?
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Old 03-25-2010, 01:54 PM   #140
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Sometimes odd sized duct has to be used.

Hart and Cooley has all their data on their website. You can download their catalogs and choose what you need.
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Old 03-25-2010, 01:56 PM   #141
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So for the odd sized stuff, is it usually made up custom, or just special ordered?
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Old 03-25-2010, 02:09 PM   #142
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You'll need to go to a sheet metal shop. And have them make up what you need.
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Old 03-29-2010, 04:47 PM   #143
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Thanks so much. I need to see what my options are. Would much prefer to order off the shelf, even online, than go custom, but extra headroom, or a smaller chase would be great. I need to do a bit more investigative work to figure out home much free space I have in the current chase... perhaps more than I think.

I am trying to figure out what size registers I have now... simple, right? Do I measure the outside edges? The register boot it connects to? The size of the louvered area?

Also, the Hart and Cooley catalog looks very interesting. What is the significance of the throw and spread numbers, higher means more, right? But how do I know what I want?

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Old 03-29-2010, 05:08 PM   #144
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The register boot size.

Floor register throw should be close to if not equal to the height of your ceiling(unless its a cathedral ceiling). Then 8 foot will work.

Ceiling registers. You want the throw to reach your outside wall, if the register is in the center of the room, or on an inside wall.

If its on the outside wall. Then you want is to have a throw to reach your floor(cathedral exception again).

Spread. Based some what on the wall area your covering. A register covering a 8 foot long wall needs less spread the one on a 12 long wall.
So spread is best picked based on the registers position to walls when parallel to a wall. or to room length/width when in the floor but not at the wall.
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Old 03-30-2010, 02:22 PM   #145
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Great information, for sure, makes total sense. Most of my registers are well enough located, but I've got a couple of odd situations.

What do you suggest for floor registers located on inside walls. What's the goal?

I have a couple of registers located effectively in a corner. In one case it is a corner between an interior wall and an exterior wall and in another case at the corner of two interior walls. What is the best situation here?

How do I go about sizing the register for the return air?

Also, previously we had talked about having a return air vent in my basement. You mentioned that because of the hot water heater, I needed to be careful as to how much return air I took from down there. I know normally the goal is to balance supply and return, or even a bit more return, but what should I do with the basement?

Thanks!
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Old 03-30-2010, 05:04 PM   #146
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Inside walls are some what the same as outside. As far as, your looking for throw. Spread is often reduced because your going to hit a perpendicular wall. So spread can be selected on a tighter basis.

Return filter grilles ideally are sized for 300 FPM velocity through them, so the filter is more effective.
A return grille only can be 600 FPM is ok.

For a basement with a water heater, or furnace that uses inside combustion air. Its better to pull a little less return then you have supply. makes the basement slightly positive pressure when the blower is running. But no worry about drawing CO into the house.
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Old 04-21-2010, 03:51 PM   #147
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At least this project is moving forward. Thanks for all your help!

So, is it OK to upgrade the ductwork, and the furnace itself, in stages? We'll be constructing an addition this summer, so would it be OK to upgrade the trunk that serves the addition now, based on the specs for the new furnace, and then upgrade the rest of the ductwork and the furnace itself in 6-9 months?

Assuming that's OK, how does this diagram look. I think it should be clear, but let me know if you have any questions. The required CFM are based on the HVAC Calc CFM report.

Not sure if all of it is as clear as I had hoped, the text on the green indicates that the duct is 6x10 - 134 CFM@.05FR and is approximately 14' long. The text on the brown indicates that it is 8x10, 314CFM@.067FR and approximately 11.5' in length. Everything else seems clearer, but let me know if not!

Any thoughts?
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Old 04-21-2010, 05:35 PM   #148
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As long as the current furnace is within its temp rise with the duct addition/rework. You can upgrade like that. Without any problem.

Your drawing shows the blue 6X10 tapping in as a tee.
If you can get a 15 tapered tap, it will work better yet.
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Old 04-21-2010, 05:37 PM   #149
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That blue one is actually interesting, the brown runs along the ceiling but when it reaches that wall, it turns up into the joist bay. It will then branch off to the blue and the green from there.
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Old 04-21-2010, 05:50 PM   #150
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Ah.
Might want to use turning vanes then. To keep the air flowing better.
2 direction changes that close are very restrictive. vanes will decrease the amount of restriction by about 80 to 90%.

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