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Increasing Supply register size?

Posted by bargainacious (My Page) on
Fri, May 16, 08 at 22:37

I would like to know whether increasing the boot and associated supply-register from a 4x10 to a 6x12 would have any negative effect on my system.
The reason I am considering this is that the old 4x10 boots were not insulted, and collected condensation in a (previously) damp crawl-space. The condensation caused mold and subsequent wood rot of the subfloor around the underside of the boot. The most severly affected wood is around a register where air flow is not vital (it's right next to the front door), and we have to replace a lot of rotten subfloor anyhow. Increasing the opening size would allow us to cut away the moldy and rotten wood.


Follow-Up Postings:

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RE: Increasing Supply register size?

The size of the duct coming to the boot is the most important factor in determining how much air will be delivered to any supply device so the short answer to your question is no no negative effects you will have less air noise but essentially the same volume (cfm) you are wrong however about that supply not being important, keeping outside air out is of the utmost importance and doors are one of the biggest infiltration points.

Here is a link that might be useful: Air Conditioning Repair made Easy


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RE: Increasing Supply register size?

Miken is correct concerning the air volume being determined by duct size & velocity.

We don't know what CFM volume is coming to the boot.
Let's say it was 100-cfm, many 4x10 floor diffusers' with a Face velocity of 600-fpm, would have an "air-discharge throw" of 9'feet & spread of 5.5'.

A 6x12 @100-cfm with a face velocity 300-fpm has only a 4' throw, spread 6.5'.

The 6x12 would need a 130-CFM with a face velocity of 400-fpm to achieve 8.5' throw with a 5' foot spread.

The terminal velocity from those diffusers' is 50-fpm.
For duct sizing view linked page
- udarrell

Here is a link that might be useful: DUCT SIZING CHARTS


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