HVAC - duct booster fans

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
We have a room at the far end of the house that is chronically colder than the rest.
I've done everything else I can (sealed/taped every joint, insulated the trunk, covered the 2 windows in plastic, etc) but I think the single supply just isn't enough for the space (corner, south facing).

For the money, I figured it would be worth trying a booster fan to at least get more air in there.
Originally I was going to just try one of these, a baseboard booster fan
http://www.aftproducts.com/AirFlow-Breeze-4-x-15-Register-B.item
mostly b/c it would be easy.But I figure the "right" way would be to add an inline fan in teh supply run, like this
http://www.homedepot.com/webapp/wcs...ct-4-_-100028788-_-202797339-_-N#.UP4EFvLNkYI
but I can't find any w/ the thermostatic controller built in? Is the only option to buy a separate switch like this
http://www.homedepot.com/Building-M...0053&langId=-1&storeId=10051#customer_reviews
and add it?

... at that point the baseboard thing is only a little more.
Opinions? Anybody use one of these? On one hand I'd think the inline deal would push more (no stats given for the baseboard unit), but I feel like there is a lot of pressure lost where the air goes from the duct up to the register and has to "bend" back around (almost a "U"), so maybe "sucking" from there would help?
You engineer guys - does it even matter where in the line the fan is?
 
When it comes time to replace the unit have load calculations done and the system installed properly. I'm guessing all of your duct work is the same size? As far as the duct fan. I would install it on the duct as close to the "core" of the system as I could. (just a guess no technical reference) and wire it up to turn on when the air handler does.
 
Are you in a 1 story or 2 story?

I'm in a 1 story ranch and we had a similar problem. One room was always hotter and another room always cold. I blew about 12"-10" of insulation in the attic. It evened the temp through out the house. All rooms are basically the same temp now.
 
The problem is the zoning in the house, not the amout of air that goes in there. Your thermostat is far away so that room doesn't get regulated like the rest.

Most houses have this problem, mostly because the bonus rooms are so far away from the return/thermostat they don't get regulated properly.

Does it get hot in the summer and cold in the winter, or is the only problem the cold?

What is the size of your AHU and the sqft of your house? I'm an HVAC designer, be glad to throw some knowledge your way.
 
Steve_Kibbe said:
Why not use a small ceramic space heater?
Click to expand...
Don't do this unless you are at home. All of the ceramics we bought melted something (plastic casing / wires). I kept them just to show people and can post pics. Funny they still work but scared the hell out of me when I realized. Every ceramic heater I've seen runs continuously and is cheap made.

We heat our 1,000 sf house now with space heaters and I'm spoiled. Our electric bill never exceeds $200 and my wife is cold natured. If you go that route though for your lacking room, any electrician will recommend to just be sure all your house wiring is good with matching awg wires or greater than the heaters you use. Just don't run 2 strong heaters on same but no less than 20 amp 12 awg circuits and you're good. And MOST importantly, be sure the heater has some sort of thermostat so it gets a break. We use 2 of the stand up radiator heaters for the main front / rear portions of the house and use the good fan space heaters where / when needed for it takes 30+ minutes for the rad heaters to heat up where as fan heaters are instant. I'm sold on the radiator heaters for continuously heating large rooms though. Besides the radiator heaters, any other heater without a really good blower fan is just a hand warmer.

As for duct fans, sounds like you might need a cleaning or replacement if you don't have any air blowing to begin with? A thermometer on the vents will tell alot.

I have a 2.5 ton gas pack heater that was installed as part of the deal when I bought my house. I ran it for 3 years but my house was built very close to the ground in 1940 and my flex ducts eventually rotted every where they touched dirt before I could get the house raised and crawl space dug out. I appraised $400+ 2 years ago to replace all my flex ducts not counting a helper and my time. I invested $200+ in space heaters and I'm well pleased. Two window unit air conditioners cool my house just as good and much cheaper than the 2.5 ton unit ever did as well. Even though I do plan on replacing my flex ducts just for the gas pack as emergency back up and putting a duct fan in that is externally wired outside for a generator in case power goes out.

My last house had gas logs on a thermostat with blower and was EXTREMELY cheap and heated the entire house with no more than 2 - 100 lb tanks used per entire winter. Hate I don't have a good fire place now for I don't trust logs even if they are ventless. Just tore out my last outstanding chimney this past weekend for it was a staircase for mice into the attic.
 
OK so more info, this may answer many questions. IIRC I've talked about this here before.
House is a classic 1-story ranch, full unfinished basement. Something like 1780sqft. It's long though, 60'. The furnace is about 18-20' from one end, making the main trunk length 35-something ft to where the 6" round line taps off. This is another 13' running from the center of the house to the outside wall where the baseboard vent is.
Typical setup where the main supply trunk runs the house midline, the runs go out to the outer walls to baseboard vents. Returns are in the central walls. No idea why it's this way, to me it would make more sense to have the supply vents in the central walls so the runs are shorter.
T-stat is in the hallway 10' from the room.
Unsure of the system capacity, I think it's a 2T at least. The trunks do narrow, start as 24, then down to 20, then 16 IIRC.
The pressure at the vents isn't bad, esp after I sealed it up. Measured w/ an anemometer it was only like 20% lower or something in the far room.
Our room is beside it and doesn't have this problem - BUT it has 2 vents and the door stays open.

I've insulated the main trunk w/ the standard wrap, but you can feel that the air at the vent is just not as hot, can also feel a difference in the temp of the ducts from below when it's running.
Plus, when it starts blowing, it takes several seconds for it to blow all of the cold air out of the ducts before it gets hot, vs the living room (which is right above the furnace) it is hot in 2-3 seconds.

I don't think it's really a pressure problem, just a combination of a lot of things. But my options are kind of limited. My hope was that getting more air flow (and hence more "hot air particles" lol would help alleviate it. Summer it's a little warm but not bad. Adding insulation is in the plans but requires alot more money and work.
 
regardless of what you do with a booster fan, the total output of the AHU remains fixed. you will essentially just be robbing CFMs from other areas of the house and using them further down the system.


before I put booster fans in, there are a few things I'd do first.

1. install better dampers at the branches so you can better balance the system
2. possibly install a zone system with multiple thermostats and actuated dampers. This is what I have and it works wonders. I have multiple thermostats which control that zone and open/close the dampers accordingly. It can even have the bonus room on AC and downstairs on Heat at the same time. It will just cycle the unit and dampers as needed to supply hot/cool air where it needs it. Retrofitting this to an existing system is likely really involved and expensive.


I'd go with manual dampers and start there. Maybe remove the insulation and install duct seal at EVERY joint. This will get your efficiency up, way up as most residential leak tests are luck to get 60% although SMACNA standards require at least 80% or so? Can't remember. I always try for 98%, which is fantastic. Then put good quality insulation on it. don't get rolled fiberglass insulation. Maybe spenda few $$$ and get some Armaflex on there.
 
rockcity said:
regardless of what you do with a booster fan, the total output of the AHU remains fixed. you will essentially just be robbing CFMs from other areas of the house and using them further down the system.


before I put booster fans in, there are a few things I'd do first.

1. install better dampers at the branches so you can better balance the system
2. possibly install a zone system with multiple thermostats and actuated dampers. This is what I have and it works wonders. I have multiple thermostats which control that zone and open/close the dampers accordingly. It can even have the bonus room on AC and downstairs on Heat at the same time. It will just cycle the unit and dampers as needed to supply hot/cool air where it needs it. Retrofitting this to an existing system is likely really involved and expensive.


I'd go with manual dampers and start there. Maybe remove the insulation and install duct seal at EVERY joint. This will get your efficiency up, way up as most residential leak tests are luck to get 60% although SMACNA standards require at least 80% or so? Can't remember. I always try for 98%, which is fantastic. Then put good quality insulation on it. don't get rolled fiberglass insulation. Maybe spenda few $$$ and get some Armaflex on there.
Click to expand...

This is right on. If you have a properly sized unit, the VAV system is RIGHT ON. It will fix your problems, my next house will have this definitely.
 
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