Booster Fan

don_102

you Wayne,I dont see how adding a return will help when you
have inadequate fan performace.

If the blower can not produce enough static pressure then there can only be one option.

Wayco Wayne

I have a customer

who has a room at the end of the houseover a garage that does not get the air flow it needs. I've done a heat load and capacity is not a problem. The problems are; 2 sharp turns in the trunk duct, just before it reaches the room resticts the air flow, and the thermostat is in the center of the house and shuts off before the extremity zone in question is conditioned. I was thinking a booster fan for the trunk duct, just after the 2 sharp turns would make things right. It would need to move 400-500 cfm. Where would I find such a device???? WW

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J.C.A._3

Granger and Sid Harveys.

They both have them in their books, but be warned...THESE THINGS ARE NOISY!!! You will also have to run a wire from some sort of switching relay to have it work when there is a call for heat, or have it wired into the fan switch circut.(long runs yeah?)

I think Tjernlund makes them. Chris

Weezbo

sheet metal shop.

having a zone valve and t stat is the simplest way to relay it...in case you want it to be a quiet system size the zone inducer(in line booster)

harvey

booster fan

Those fans ARE noisy but we have used Fan Tech fans. Have you tried running the fan constant? Have you dampered off most of the rest of the house? Does the duct feeding the problem area come right off the furnace? Depending on the layout of the duct, you might need a poke damper to scoop the air into the duct for the problem area.

Wayco Wayne

Thank you all for

the input. This duct is at the end of a long trunk run and of course is all covered by finished drywall. The duct turns up and then out to get into the finished garage ceiling where I had to cut open a bulkhead to cut open the duct to stick my melon head in with a spotlight. Nice 8 x 12 duct. should move 400 cfm but it don't due in part to the 2 sharp 90's and mayby due to an undersized furnace for the duct size. (Don't know the ducts are all enclosed. I was thinking of just adding a separate 1.5 ton heat pump system, but I feel it would be overkill. They could afford it though. The man of the house is the producer of the TV show, "America's Most Wanted." Nice folks. Been my customers for many years. WW

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Rich W

fan

You don't mention a return duct. Is there one? I've seen a lot of rooms like this that don't. Do they keep the door closed? If they close the door,it's kinda like trying to blow into a Coke bottle if there isn't a return. I've had customers that didn't want the bottom of the door shaved- installed back-to-back return vents in the wall.They were very happy with the price too...lots of W.O.M. PR. Good luck,these are a bear with finished walls.

Wayco Wayne

Rich

You're good. There is no return in the room however I have had them put a gap under the door and leave the door open all to no avail. I'm thinking maybe a larger furnace blower now. Hmm. WW

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Mike T., Swampeast MO

Any way at all to add a ducted return? I solved that exact problem just by adding a return--this after the homeowner tried to compensate by leaving doors open. This was a new system in a freshly renovated/expanded older home during the cooling season, so don't know about heating performance.

Air can get awfully lazy. In the case I mentioned, not only was supply velocity low, but the supply seemed to just be short-circuiting back to the system without mixing well in the space. This was especially noticeable with A/C, but suspect there would have been a similar problem with heating.

don_98

Please

forgive me if I come off sounding like a butt head not my intention.

Wayne,if I may for a moment in steer to away from the booster fan,biggest piece of crap ever invented.Save your time and the customer money.

Lets assume here that the customer added a high static filter one that was not design for the distribution system.
Lets also assume that there could be a possibility that the
coil and blower may have tons of dirt on them that is adding too the lack of airflow coming from the system.

Lets also assume that the guy that put in the distribution system made not ever done a manual D calc and work solely
off a duct calcualtor that was made for metal,but yet he used lots of flex instead of metal.

Now thats we had assume all the possibility,what would be our next course of action to take?

I would think you would want to check the static pressure across the system first and see if the blower can handle
all the resistance that it working against and still deliver the proper cfms.

Only then will you be able to address the issue at hand.
Again just trying to be helpful.

S Ebels

No return?

If not, this is an unwinnable situation. There is no way it will work. If the returns are in the other part(s) of the home, the air will stay there. It really behaves a lot like water in that regard. Think of a radiator with no return line.... (OK that's a slight exaggeration) but it's nearly as effective. If you try to increase the blower speed and therefore the static pressure in the duct it'll still take the path of least resistance.

Solutions: Small independent system of some kind for that area of the home.

If it's a heat only job, maybe a small boiler/water heater and a couple panel rads along with heat to the garage below as a bonus.

Wayco Wayne

Steve and Mike

What is the difference in having a return and just having the door open so the return air has a path back to the central return. I'd say none. With the door wide open I have just a breath of air in the 5 supply outlets in the space. If the door was closed I'd understand that the room would pressurise and stop air flow. But with door open I should have none of that. WW

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Mike T., Swampeast MO

Just because you've given the air a path to travel doesn't mean that it will follow.

High pressure flows to low pressure, but it also takes energy to move the air or water. The energy it takes to move the air shows back up as a decrease in the pressure differential.

If the path is easier from the central return to the supplies in other rooms, the blower will satisfy its differential by receiving return air mainly from those spaces--not the big room over the garage. When that happens the supplies in the big room "see" very little differential pressure and velocity slows to a crawl. Give it a new, separate path to low pressure and velocity in that space will increase while it decreases in the rest. If everything is well-sized, you'll get balance.

Mike T., Swampeast MO

Not seeing the job it is a bit rough to speculate, but inadequate/improper returns are the nemesis of forced air systems.

Another example:

Was working (not heat related) in a customer's new home one coolish evening. Rather large place with volume ceilings and two forced air systems. One system was for the 4-room master suite and the other for most of the common space and remaining bedrooms. Thermostats for both in wide hallways on either side of a large entry hall and family room.

Was sweating my a$$ off just doing modest work. Owners not home so opened doors and shut off the heat. T-stat for the master suite was set around 80°; the other around 75°.

When owners got home asked what was up with the really high t-stat setting. They said it was the only way to get the master bath warm. Went in the bath--door was open and they said it stayed open. Huge space with an exercise area. At the front of the house with two exposed walls and a number of large windows. Electric "floor warming" for the tile floor. I was decidedly cooler.

Looked at the ductwork. Found two supplies, but no return. Toilet area completely compartmentalized. Suggested that they have a return added.

It worked.

S Ebels

Let's assume

The following: The blower is developing enough static pressure to overcome the resistance to flow in the affected area. Let's also assume that the duct system has dampers that allow airflow to be balanced throughout the system. Same static from one end to the other at the discharge points.

For the sake of this discussion let's say there is one main return located on one end of the house. Which side of the house is going to heat the most evenly? The side with the return wins every time. I can't tell you how many el-cheapo FA jobs we have fixed when the proud owners of the brand new house complain about temp differences of 5-8* from side to side in the house. The fix is adding returns 9 times out of 10.

All that being said Wayne, it's difficult to say without laying eyes on your job and you may have other problems. These could be a large difference in heat gain/loss from the area in question. Unheated/cooled space below.......who knows? You might try installing balancing dampers and see what happens if not in there already. I just know from experience that I've never seen a house with too many returns.

The only systems I've ever seen work with a single point return are the Hi velocity types. (Unico, Hi-V, Space-Pak etc.) They will literally blow (aspirate is the term) the air out of a room and push it back to the return.

Wayco Wayne

I'm going back today

to check the furnace and pull the evap coil. I have no static to the end of the run and the whole trunk enclosed in drywall, so no balancing dampers are accessable. I want to make sure the evap coil isn't clogged and check the number of branch ducts on the system relative to the tonnage of the blower. Thanks for your input. It really helps to throw things up on the Wall to mull things over. WW

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