Quick HVAC Airflow Question

[kamikazekyle]

I have one or two duct runs in my house that could use a little umph on airflow output. The air is properly cool/warm, just that the airflow could be improved.

I looked into powered registers (registers with 5V DC fans in them), but the reviews are all over the place. Plus one of the areas that coud use some extra airflow is large and with no doors, so I don't think a powered register(s) would make much of a difference.

Note that these areas have <1 year old flexducts that were professionally run and sealed, so the ductwork is OK (could reinsulate my main, however).

How fesable for a DIY is it to upgrade the blower in the inside portion of a heatpump setup? Or should I go for something like an in-line booster fan (http://reviews.homedepot.com/1999/100067594/6-in-in-line-duct-buster-fan-reviews/reviews.htm)? Or stick with a powered register?

After forking out $20k for structural work and another $15k+ expected within a year, I'm trying to keep the other house costs down, so it has to be a DIY solution

 

[iGas]

Check to make sure ductwork are not block, return air opening must be clear of obstructions such as furnitures, carpet, plant, etc...

Check & replace the filter regularly (3-4 months per replacement). Throw out the washable/reusable filter and put pleated paper filter in place.

The blower can be set to ignore low fan speed and run at medium & high speed only, however that will increase noise an lower efficiency due to higher cycling frequent of heatpump, if you have a multi speed blower (higher CFM blower can be install if the unit can except it, but it would just increase noise if duct work is not redone and doesn't give you much more air flow).

Many return duct work and opening are undersized because of laziness or lack of surface area for opening (you can increase the ductwork size and opening, however we must know the heatpump blower CFM & tonnage).

Duct work rarely are size/engineered for length of run or load for residential because it is an expensive process (most are taken from a generic table number), and then there are short cuts and human factor errors (flex ducts also cut down the airflow due to friction).

It is cheaper to buy another house or built a new house if you don't like the air flow, because rip everything out to redo the ductwork is expensive.

The fan in your link is generally use to increase length of duct run. It is not expensive or difficult to install, however it need power to run. I supposed that you can install 1 in every branch but that wouldn't increase air flow if the return air ductwork and opening isn't enlarge.

 

[kamikazekyle]

Thanks for the reply, iGas.

-Registers are unblocked; I even removed the vanes/plates that are used to adjust airflow. The inside of the ducts are clear, barring something the install crew left behind inside the ducts.
-Filter is 3M pleated paper (not the reusable/washable ones), replaced about every 3 months.
-Return is located in the ceiling, right next to the blower closet. No vents nearby. The return duct goes up into the attic, loops over a beam, then hits the blower. I'm not sure on the size of the return duct in inches, but I'd estimate it to be about 12" inches in diameter?
-Filter size is 24"x14", or thereabouts (can't access my springpad at work, but it's within an inch or two)
-I don't think I have a variable speed blower. The HVAC system (sans ductwork) was newly installed before I bought the house. I'll have to grab the make/model and look up more information. It is a 1.5 ton unit, which is about right for my square footage and temperatures.

One thing I haven't tried is to inspect my main for leaks. It does need reinsulating, that I can tell from a distance, but I have yet to crawl through all the pipework in the crawlspace to close-inspect the duct. I could have leaks in the main as that wasn't replaced with the heatpump/blower/return when I bought the house, and could be >40 years old.

I'll probably go through and inspect the main for leaks and double check the ductwork connections once they're done doing the crawlspace repairs. Especially since the main area of their work is near the main and the majority of my plumbing.

 

[iGas]

Thanks for the reply, iGas.

-Registers are unblocked; I even removed the vanes/plates that are used to adjust airflow. The inside of the ducts are clear, barring something the install crew left behind inside the ducts.
-Filter is 3M pleated paper (not the reusable/washable ones), replaced about every 3 months.
-Return is located in the ceiling, right next to the blower closet. No vents nearby. The return duct goes up into the attic, loops over a beam, then hits the blower. I'm not sure on the size of the return duct in inches, but I'd estimate it to be about 12" inches in diameter?
-Filter size is 24"x14", or thereabouts (can't access my springpad at work, but it's within an inch or two)
-I don't think I have a variable speed blower. The HVAC system (sans ductwork) was newly installed before I bought the house. I'll have to grab the make/model and look up more information. It is a 1.5 ton unit, which is about right for my square footage and temperatures.

One thing I haven't tried is to inspect my main for leaks. It does need reinsulating, that I can tell from a distance, but I have yet to crawl through all the pipework in the crawlspace to close-inspect the duct. I could have leaks in the main as that wasn't replaced with the heatpump/blower/return when I bought the house, and could be >40 years old.

I'll probably go through and inspect the main for leaks and double check the ductwork connections once they're done doing the crawlspace repairs. Especially since the main area of their work is near the main and the majority of my plumbing.

The rule of thumb suggests that your blower is 600CFM (possibly greater CFM) for 1.5 ton.
Supply trunk should be 12" round duct, and return trunk should be 13" round duct (14" is the size that you can get).
Opening will determine by the type of grill that you use (30-45&#37; greater opening size than duct due to grill/s restriction).

Good luck!

 

[Tdad]

Also, if possible, call an energy auditor to do blower testing and make sure that all ducts and the whole house are air tight, otherwise, you investment may get wasted due to air leak.

 

[kamikazekyle]

Well, the HVAC bit is kinda on hold now. The structure repair teams are doing their thing this week, and have pretty much disconnected my entire duct system and main trunk without telling me. I was making my crawl space all nice and warm yesterday. Who knows if they're going to seal it back up correctly like the original HVAC team did. They also pretty much destroyed the vapor barrier I had installed, but according to contract they're supposed to seal that back up.

Considering the team that was last in mixed concrete next to my car on a windy day, splattering it with wet concrete that solidified into some bad water stains, I'm not having good faith. I'm certainly going to take a good look before I cut the check at minimum.