HVAC Help

[bfisher]

Thanks for the great information - now I understand.

Do you think adding a ductfan to a plenum is possible? Would it be worth it? Seems like it would help a little - but probably not as much as if I could attach it to the ducts that actually went to the rooms... I think I'd have to rip out sheetrock to gain access to the ducts

 

[kwilcox]

Like I said, you'd probably have to remove a section of the plenum and insert a fan between the two parts. Would it make a difference? Absolutely. Remember that your average diffuser is designed to flow about 100CFM. Here's a link to FanTech's site showing airflow specs for their inline centrifugal fans:

http://www.fantech.net/fkd2.htm

The air performance graphs are especially interesting as they show the fan's performance as the downstream plenum is pressurised. As you can see, these products can flow a lot of air even when the downstream plenum is heavily pressurised.

These devices aren't cheap though; I believe the 8inch fans run around $700. You also may need a downstream duct muffler to eliminate fan noise. I have two on my current installation. Here's a picture showing this:

 

[bfisher]

Again - excellent information - I appreciate your patience in explaining this. In looking at the Fantech site more (one I originally stumbled upon and was interested in) - they do have some fans made for square/rectangular ducts (FRD and FSD series) - so this might be the best route for me.

Mentions adjustments for system balancing... this makes me a little nervous. Still leaning towards having a professional install this - I don't want to ruin my HVAC unit.

 

[bfisher]

OK - I'm still working on this one This latest heat wave has convinced me this is a higher priority project than originally planned.

I have measured the plenum ductwork (it's insulated) but best I can tell - it's 12x6. I see Fantech makes a FRD12x6 Rectangular inline fan. Output is ~300 cfm (which I'm guessing is 3x normal HVAC fan output). Do you think that's enough improvement when the fan will be in the basement, and it needs to blow up to the second floor? 3 times what is coming out of the vents now would be an improvement if all the improvement makes it up that far. I assume there will be some loses (plus pushing condensed air)

Second question - tracing the ductwork - there is a duct merging into it which best I can tell is an overflow pressure regulator (my HVAC has 3 zone dampers). I assume I need to install the fan AFTER this duct (otherwise it will pressurize the overflow and it will never work). Does this make sense or am I way off?

Thanks again

 

[AutomatedOutlet]

Hey, I'm looking at carrying automated registers. It looks like a great idea. I'm meeting with the president of the company net Tuesday. What do you think??

 

[bfisher]

By automated registers - I assume you mean a fan is installed in the register itself? or is it opening and closing the register?

If it is a fan in the register - it's a great idea if it's quiet and moves the air. Would probably work for my needs! and should be simpler to install... (power will be an issue for me. All of my second floor vents are mounted high up on the wall. However, there is usually a closet nearby that I can probably run power up through to get it close).

If you don't mind - keep me posted how this goes for you. If you want me to take a look (since I know I have a need), send me a link or email me some information.

 

[kwilcox]

By comparison, your average register with 6" ducting is designed to flow 100 CFM so the fantech will flow as much as three of them. To me that seems a little on the low side however it all depends on how many rooms are on the downstream side of the fan itself. Since your plenum is only 12X6 I'd imagine that there aren't more than a couple of bedrooms on it so you may be good to go. Another thing I'd be worried about is fan noise. I don't know of any duct mufflers designed for plenum. You may not have an issue with noise but its always nice to know that you've got options.

As far as I can tell, you're correct about placement (downstream of your overflow duct). The system I use flows about 1400 CFM at full bore btw.

 

[kwilcox]

A nice thing about register fans is that they're also pretty efficient since there is essentially no exhaust pressurization.

 

[AutomatedOutlet]

Here's a link to what we'll be carrying - http://www.automatedceilingregisters.com/air_flow.htm

It's nice because it only uses power when you are changing the setting.

As far as installing it and running the wire, the owner of the company was telling me that the way they do it is to open the duct by the airhandler, and tying a string on to a ballon that's inflated about 4 inches. Then put the duct back on and turn on the system. The air movement will carry the ballon out the register! Cool way to do it I thought!

 

[bfisher]

These look really slick - but won't help me

I have a zoned HVAC system already - so I don't need the ability to shut off vents. What I need is a fan inside the vent to increase airflow blowing through the vent. So instead of just opening/closing the vent - I want a fan back there

If I didn't already have a zoned HVAC system - this would definitely be interesting to me! I'm sure you will have other people that this is perfect for.

 

[electron]

Martin, do you have any pricing info yet? This sounds like something I have to research.

 

[BraveSirRobbin]

Yes, I may want this as well, but my register cover's are "square" and some of the larger ones have four mounting screws. Do these come in different sizes other than the "standard" rectangular mount shown on their site?

 

[kwilcox]

If anyone adds a bunch of these, don't forget to also put in a bypass somewhere or you can burn out the primary blower motor.....

 

[BraveSirRobbin]

Yea, good point, I was only going to put these in areas where I needed the flow reduced (exit point on end would not be altered).

 

[bfisher]

For anybody that was following this topic (original thread: a couple rooms on the top floor of my house was not getting enough cold air from the HVAC system (located in the basement)).

I installed a Vent Booster Fan to help with airflow in the short term (with plans of installing an inline duct fan over the winter when I have more time).

This little booster fan works great for my needs, and I would recommend one to anyone that needs a little help. Once you adjust the controls, it kicks on about 1-2 minutes after the AC comes on, and turns off about 1-2 minutes after the AC turns off. There is some noise, similar to a deskfan running, but it's not too much.

It has really helped getting cold air upstairs... but it only helps in the one room that it is installed in. However, in general, it is cooler upstairs now and it seems to have helped circulation overall up there.

The only negative to it - it needs to be plugged in, and my register is mounted high on a wall. So right now, there is an ugly extension cord. If this was to be "permanent", I would want to run an outlet up to there. However, I plan on putting in a in-line duct fan early next year when I get a free weekend.