Random HVAC Question

kevhed72

So there are different vent sizes for both return and delivery of air, as there are different duct diameters. Down here in hazard county we are required to have the silver circular insulated ducts.
Question is:
If I simply INCREASE the vent/opening size in the wall for a return OR delivery vent.....will this increase airflow to/from furnace?

afterburnt

All that junk is supposed to be balanced, you can't just randomly make changes and maintain performance and efficiency.

gmcman

You will be limited to the ducting just before and aft of the air handler. All things being equal, with what you described you will likely feel a difference in velocity on the output.

Pics would help, something as simple as a radiused ducting on the discharge of the air handler would be much better than a right angle. Really depends on your setup.

Lengrh of ducts, how many bends, etc makes a difference.

I'm assuming cold rooms during the winter?

mrbigbluelight

Any of those ducts have balancing dampers on them ?

rpf65

When it comes to ducting, you can't have too much return air. You can have too little, but not too much. Reason is that if your furnace/air handler is capable of outputting 3000 cubic feet per minute, and your return air is only capable of 2500 cubic feet per minute, your starving the system by 500 cubic feet per minute. If on the other hand, your return air can supply 3500 cubic feet per minute, and your furnace needs 3000, your good.

The vent size does play a part, again, a hole is only so big. in this case, if the hole, grill size, is only big enough for 2500 cfm of air, and you need 3000 cfm, you starve the system of air. Usually you can tell if you hear a noise by your return air grill, but its best to measure the static pressure.

When it comes to supply, its similar, but backwards. you need large enough ducting to get adequate air flow, but too large or small of ducting will effect the air flow. Looking at total capacity, and simplifying everything, if you have a 4 ton furnace, and only ducting capable of delivering 2 tons of air, you get 2 tons of air, and a lot of noise. that's all the air that the ducting is capable of handling. simple, and makes sense.

On the other hand if the duct is too big, 4 tons of ducting for a 2 ton system, the static pressure is too low. that means the velocity of the air flow is too low. So if your bedroom, for example, is 16 feet wide, and your supply vent is 1 foot from the wall, you want that air to travel about 14 feet.

If the air travels 8 feet, for example, the far side of the room will feel a lot warmer than the side closer to the duct. Not good, and generally upsets people. There is room to play with duct sizing, but that gets a little complicated.

I think what they a referring to is the insulation value of the ducting. Many places want R-8 installed, when ducting is replaced, R-6 is the most common that has been used for the last 20 years or so. This is in reference to flex duct.

My best guess in the "R" value increase of a 2000 square foot house would be less than 1 percent energy savings in the Austin Texas area. We get quite a few days 100 and above in a typical summer. So if you're looking to lower energy cost, and your duct work id good, not worth replacing it.

As far as supply grill sizing, most grills are sized for the buckets. Want a larger or smaller grill, you have to change the bucket. that's the part the duct connects to the duct.

Dabutcher

I replaced my central air system by myself. I just used like for like components and it works fine so I am no help. I did learn in school to get EPA certified to work on machines with refrigerant that you should replace your furnace filter every month. Saves on problems down the road. And don’t buy the cheapest filter. Go with at least the $3 one that is paper. Good luck. D

kevhed72

mrbigbluelight wrote: »

Any of those ducts have balancing dampers on them ?

. The ones I am considering changing...no. We have a cold "side" of the basement with 2 windows and a door to the outside.

VR3

I'd look into a mini split