# Anyone ever install this in-duct fan?  Need your input HVAC guys



## 04RevX (Oct 20, 2010)

http://www.smarthome.com/3011/6-In-110VAC-250CFM-In-Line-Duct-Fan-DB200/p.aspx

Here is what I have in mind.  I have a ranch and my wood stove is located at one end of the house.  In order to heat the rest of the house the room that the wood stove is in gets really hot.  I'm thinking of cutting in some duct work in the ceiling where the wood stove is located, run 6" diameter flexible aluminum ducting (and insulate it), install this fan at some point in the run, and dump it through the ceiling at the hallway at the other end of the house.  I just want to distribute the heat a little better.  Fans on the floor work but I hate the way they look.  I would throw this on a switch and flip it on and off when necessary.

Couple of questions....

Is the flexible aluminum duct work ok to use?  The package says it can be used for a/c, heating, or exhaust so why not??
I'm thinking a 4x10 register in the heater room.  This size just looks right to me, do you suggest anything else?
Where in the run should I install the fan?  My thought would be closer to the room that its pulling from.
Is 250 CFM enough?  To get 500 cfm I'd have to go up to 8" duct work.  But i've only looked at Home Chepo.

I'm onlying going about 25'.  Thanks in advance for the input!


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## RnG17 (Oct 20, 2010)

I'm an HVAC tech. The idea will work. And your right with all the numbers. Personally I might go with an 8", but thats me. How big is the room you are trying to heat at the other end of the house. As far as the 4x10 grille goes, here again I might go a big bigger, in some cases you will hear air flow going through the grille if the grille is too small. I would shoot for the 300 to 350 cfm range, not sure what kind of fan your getting either, we don't install them very often at my company, but maybe you can get one that is multi speed and then you can change it from low to high to get the heat that you want. I guess what I'm thinking is, if you spend the money and its still a bit cooler than you want, your going to be upset, if its warmer than you'd like there are ways to fix that without spending a lot of money.

Just my 2 cents.


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## fdegree (Oct 20, 2010)

My profession is air flow...primarily commercial and industrial HVAC, but air flow is air flow.  That being said, I don't think that fan is going to give you the performance you are looking for.

250 CFM through a 6" duct is 1,250 FPM...that is a high velocity for such a small fan.  If you look at the Specifications table, it shows 2 different CFM performances...one is labeled Max Boost CFM, and the other is labeled Free Air CFM.  The max boost CFM (250 CFM) is the expected performance if it is installed in existing duct work where it is boosting what the air handler fan is providing...2 fans in series.  The free air CFM (160 CFM) is what you can expect from it in your proposed application...no assistance from another fan.  So, in your situation 160 CFM is probably more realistic from this fan.

I will try to answer your questions based upon the fan you are proposing to use.  These answers could change if you decide to go with a different fan.



			
				04RevX said:
			
		

> Is the flexible aluminum duct work ok to use?
> The package says it can be used for a/c, heating, or exhaust so why not?


Yes, the flexible aluminum duct will work.  But, will it be insulated...if not, you may loose a lot heat (Sorry, I just reread your post and noticed you said it will be insulated).  I'm not sure if something like this would be cheaper.  *Insulated Flex Duct*



> I'm thinking a 4x10 register in the heater room.  This size just looks right to me, do you suggest anything else?


The 4x10 register is fine for 160 CFM, but a little small for 250 CFM...you may hear air noise from it if you are moving 250 CFM



> Where in the run should I install the fan?  My thought would be closer to the room that its pulling from.


I think you are right.  It is easier for a fan to push air than it is to pull air.  So minimizing the length of the duct on the suction side of the fan will help its performance.  But, if you have it too close to the register, you may hear the fan running...which can be annoying.  Also, with aluminum duct, you may get echoing of the fan noise.  The insulated flexible duct may absorb some of that noise.



> Is 250 CFM enough?


Without knowing your floor plan and room sizes, this is hard to answer.



> I'm onlying going about 25'.


Actually, that is a long way for the aluminum flexible duct...for any flex duct for that matter.  The smoother and shorter the duct the less restrictive it is.  The aluminum flexible duct has a lot of ridges on it, and 25' is quite a distance to run any flex duct.  As a result of both of these factors, the fans performance will likely be reduced.  This is purely a guess, but instead of moving 160 CFM, the performance could be reduced to 125 CFM.  No way of knowing for sure without actually taking air flow readings.


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## 04RevX (Oct 20, 2010)

Awesome answers guys...with the proposed setup up my material cost would be around $200-$250.  This was the only type of in-duct fan that home depot offered.  I'm an electrician and work with HVAC guys here and there.   I've wired up several commercial duty in-duct fans but these suckers were big.  I agree with going bigger...rather have too much than not enough.  I'm going to go to a supply house near hear that sells HVAC equipment and see what I can get my hands on.  Thanks again.  I'll update this if and when I eventually do this.


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## fdegree (Oct 20, 2010)

Upon further investigating, I think I may be wrong with one part of my reply.  I think the Free Air CFM rating is the expected performance of the fan when there is NO ductwork attached to it.  Once you hook-up ductwork, this performance is going to decrease.  In the specifications table, there is a link to a performance chart (fan curve) for that fan...it shows about 160 CFM at 0" w.c. (resistance).  Looking at this performance chart, 90 CFM may be more realistic with the ductwork and registers installed.

Also, just a thought, perhaps you can use a speed controller (similar to a dimmer switch) instead of a simple wall switch.  Just make sure the fan can handle a being slowed down by a speed controller.


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## DanCorcoran (Oct 21, 2010)

Since the fans you referenced are cheap ($30), why not put two in series?


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## blthomas (Oct 21, 2010)

I'd like to hear input on Dan's ^^ thoughts myself.  

We currently run a Harmon in the basement, I have a 1 level ranch, with full basement.  

Basement is 95% finished.  I have transoms over the 2 bedrooms down there.  I keep the door open at the top of the stairs.  The 3 bedrooms in use upstairs, are above where the stove sits downstairs.

But our great room is on the far end, stays cool, and I'd like to draw from right above the stove while pushing air into that room.  But that means ducting at least 25 or 30 feet.  And that puts me near the stairs, I'd like to vent it on the far side of the room so the cold air can go downstairs.  

So ducting maybe 45 or 50 feet.  Put in 2 vents in the floor, just to push the warm air in. 

I do have insulation in between floors from previous homeowner, as well as drop ceiling I installed over the last 2 years.

I was going to start a thread, but with a similar idea as 04revx, maybe I can ride the coattails here if that's cool.
Thanks,
Blair


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## coldairguy (Oct 21, 2010)

http://www.grainger.com/Grainger/inline-duct-fans/fans/hvacr/ecatalog/N-8x8


I'm an HVAC guy as well, sounds like a good idea....check grainger out.


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## fdegree (Oct 21, 2010)

2 fans in series are NOT additive.  But, they are able to overcome addition resistance while maintaining their rated CFM performance.  Theoretically, the performance will be the rating of the first fan only.  Also, with series fans, if they are not sized and installed correctly the fans may start pulsating, reducing performance and increasing noise.

2 parallel fans ARE additive.  Meaning, if you install 2 fans, side-by-side, you can add their rated performances together to determine the total output.  But, they will not be able to maintain their additive CFM rating if they are to overcome any additional resistance.


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## jeff_t (Oct 21, 2010)

What about going the other way, blowing cold air through a register near the stove? Like a cold air return. Same as what you would do with a fan on the floor that blows toward the heat, only not tripping over the fan. I've thought about doing this when I build a hearth in the next couple of years. I'd put a register behind the stove somewhere, in a corner install.


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## DanCorcoran (Oct 21, 2010)

The licensed installer who did the Radon remediation in our previous home in Colorado stacked two of those FanTech fans (in the Grainger catalogue link)  to get sufficient draft.  They worked well (and are warranted for 24-hour operation for 10 years, as I recall), but they are expensive and noisy, depending on the model.  (Check out the "sones" rating of a fan before buying, if noise concerns you.)


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## northernontario (Oct 21, 2010)

I just installed one of these specifically to move air when heating with the wood stove.  While it's not pushing 260cfm, it does move a decent amount of air, and is fairly quiet.  Even if it's only moving 120cfm, it's much quieter than an equivalent bathroom exhaust fan that moves 70cfm.  

My setup... stove is in the basement near the stairs.  Stairs open into the hallway/living room.  Part of basement has 8ft ceilings, part of basement has 6ft ceilings.  At the 'transition' to 6', you can see the backside of the drywall for a rear wall... I had previously cut a vent into that wall into the basement for cold-air return (planning to extend the furnace cold-air return to it), since the room is poorly heated in the winter due to excessive duct length @ small diameter ducting.  Well, instead of hooking to the cold air return, I made up a piece of sheet metal with a 6" takeoff, fastened it to the studs (backside of the wall), mounted the fan to the 6" takeoff, and then a 6" elbow to point to the ground.  

With the fan off, there is still a natural draft through it (cool air falling into the basement, hot air rising up the stairs).  With it running, it pushes the cool air into the basement, moving more warm air up the stairs.  

And comparing fans... that one draws about .25A... versus a noisier bathroom fan that draws over 1A.  (tested both on a watt meter)

Just remember, the longer the pipe run, the more restriction you'll get.


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## Troutchaser (Oct 21, 2010)

Great post.  I've many of the same questions.
My thoughts were to pull cool, humid air from the basement up to the stove room, which can be overly warm and dry.
Thus, the basement is heated by sucking that warmth down the stairs.  Maybe eliminate the dehumidifier down there???
And the stove room (house) can be cooled on those nights I get it a little too warm.
Not hi-jacking.  Hoping to add to the conversation.


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## DanCorcoran (Oct 21, 2010)

Pushing heat down and pulling cold air up sounds like a "challenge"...


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## mayhem (Oct 21, 2010)

I've been considering doing something like this myself for a couple years now.  I was thinking of putting the ductwork so that I'm moving cold air out of the back bedrooms, through a duct and have it exhaust right behind the woodstove.  This should create a negtive pressure in the bedrooms and a positive pressure in the great room and thus force warm air down the hallway and into the bedrooms, right?

This has been beaten to death with the fan on the floor conversation, time and again we have all seen that its more effective to evacuate cold air out of the unheated room instead of trying to blow warm air around the house, right?  I suppose it would be easy enough to simply reverse the fan to reverse the airflow, right?

Sounds like smooth ductwork, bigger registers and a bigger cfm fan might be the ticket here.

To the HVAC guys, what sort of numbers do you need in order to run some calculations to arrive at the right fan size?


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## fdegree (Oct 21, 2010)

I agree with Dan...trying to move cool air up and warm down is not likely to happen naturally.

Putting box fans on the floor is an entirely different situation.  What I'm going to discuss here is what seems to be the topic at hand...fans with ductwork attached.

Now, my specialty is with traditional HVAC equipment, so this concept of simply moving air to accomplish a certain heating task is a little different than I'm use to dealing with.  I will try to give my thoughts on the matter, but keep in mind, I may overlook something.

The way I see it, there are 2 options:
1.  Pull warm air from above the stove and dump it in the desired location
2.  Pull cool air from the floor level of the desired location and dump it near the stove

I would think that option 1 will be the most efficient.  Why?  Well, we must look at option 2 for the answer:
If you pull air out a room, that air must be replaced with air from someplace else...the "replacement" air will come from the least restrictive path...if that is through leaks around windows/doors/etc., you could be pulling cold, outside air into the room you are trying to heat.  Granted, the stove room will become pressurized, and some, not all, of that heat will migrate to the lower pressured room.  But, if you have a leaky home, some of that heat will be pushed out through leaks around windows/doors/etc. in the stove room.  Also, if the wind is blowing outside, what room is the wind hitting first...if it is the room you are trying to heat, then your "replacement" air will come from outside more easily.

With option 1, you are pulling warm air directly from around the stove and dumping into the room that needs the heat...there is no question where that warm is going to end up.

I hope this helps...if not keep firing away...I'll do my best to answer what I can.


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## fdegree (Oct 21, 2010)

mayhem said:
			
		

> I suppose it would be easy enough to simply reverse the fan to reverse the airflow, right?



Well, it depends upon what you mean by "reverse the fan".  If you mean take the fan out of the duct and turn it around...yes, you are correct.  If you mean reverse the rotation of the fan...not necessarily.  Reversing the fan rotation on a propeller type of fan will reverse the air flow.  But, reversing the fan rotation on a squirrel cage type of fan will NOT reverse the air flow...it makes the air flow more turbulent and the fan less productive.



> To the HVAC guys, what sort of numbers do you need in order to run some calculations to arrive at the right fan size?



A floor plan layout and room sizes.  Include the location of the stove, ceiling heights, window locations, door locations and your desired results...EDIT: insulation values in floor, wall and ceiling, average winter outdoor temp..  Again, keep in mind my specialty is with traditional HVAC equipment.  So, my confidence level with this type of application is marginal.  But, I'll do the best I can.

Perhaps there are others with more applicable knowledge that will chime in.


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## vvvv (Oct 21, 2010)

mayhem said:
			
		

> I've been considering doing something like this myself for a couple years now.  I was thinking of putting the ductwork so that I'm moving cold air out of the back bedrooms, through a duct and have it exhaust right behind the woodstove.  This should create a negtive pressure in the bedrooms and a positive pressure in the great room and thus force warm air down the hallway and into the bedrooms, right?
> 
> This has been beaten to death with the fan on the floor conversation, time and again we have all seen that its more effective to evacuate cold air out of the unheated room instead of trying to blow warm air around the house, right?  I suppose it would be easy enough to simply reverse the fan to reverse the airflow, right?
> 
> ...


>.6 btu per cubic foot air with a 50* differential [20*-70*f]. not a linear equation but workable in this range ithink. 10* differential might be .12btu/cubic foot air?


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## Troutchaser (Oct 21, 2010)

I understand the challenge of pulling warm air down.  .
But if I run a short piece of duct with a 250cfm fan up from under the stove area, that air has got to be replaced with something.
In a finished basement with solid concrete walls, no windows, one door, where is that replacement air going to come from if not from the wide open passageway that leads down from the stove room.

I realize that it isn't an ideal way to try and heat the basement, but I see possible benefits.
Everyone is trying to get heat upstairs and here I am trying to get it down.


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## fdegree (Oct 21, 2010)

Troutchaser said:
			
		

> I understand the challenge of pulling warm air down.  .
> But if I run a short piece of duct with a 250cfm fan up from under the stove area, that air has got to be replaced with something.
> In a finished basement with solid concrete walls, no windows, one door, where is that replacement air going to come from if not from the wide open passageway that leads down from the stove room.
> 
> ...



I sometimes I tend to over analyze things, thus making it more difficult than it truly is...forgive me if I seem to be doing that here.

Correct me If I have misunderstood...you're thinking about installing a fan that will pull air from the basement level and dump it at floor level of your living space (near your stove) on the 1st floor.

If I am correct, your "replacement" air will likely come from the air that is at floor level on the 1st floor.  With the basement air being dumped on the 1st floor, at floor level, will that basement air just recirculate back downstairs?  If not, is air at the floor level, on the 1st floor, warm enough to accomplish what you want in the basement?  Depending upon the size of your basement, I'm wondering if 250 CFM is sufficient to make much of an impact.


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## Troutchaser (Oct 21, 2010)

Ya, fdegree, that's pretty much it.
That 1st floor will be feeding the basement; however, the room is cathedral and the stove (and where I'm thinking of dumping basement air) is in the opposite corner.  I don't think I would simply be returning the same air.  It would have to mix.  Plus, the stove has a blower and there are always two ceiling fans overhead running.
The Leyden likes to run hot and it can get uncomfortable in that room upstairs.  I'm thinking that this might possibly be a solution to relieving some of the heat in the stove room and warming the basement some in the process. Maybe on a weekend when the boy is down there with some buds or something.
Basement holds approx. 7000 CF of air and is laid out that the air would have to travel through the entire basement before getting to the in-line fan in my office at the far end.
I don't know.  But I'm not convinced it won't work.

And I sincerely apologize to the OP for what I consider to be an official thread hi-jack.


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## fdegree (Oct 21, 2010)

Troutchaser said:
			
		

> Ya, fdegree, that's pretty much it.
> That 1st floor will be feeding the basement; however, the room is cathedral and the stove (and where I'm thinking of dumping basement air) is in the opposite corner.  I don't think I would simply be returning the same air.  It would have to mix.  Plus, the stove has a blower and there are always two ceiling fans overhead running.
> The Leyden likes to run hot and it can get uncomfortable in that room upstairs.  I'm thinking that this might possibly be a solution to relieving some of the heat in the stove room and warming the basement some in the process. Maybe on a weekend when the boy is down there with some buds or something.
> Basement holds approx. 7000 CF of air and is laid out that the air would have to travel through the entire basement before getting to the in-line fan in my office at the far end.
> ...



This may not even be possible for you, but...

Can you utilize the wall cavity, between 2 studs?  Put a register in the wall beside the stove...use that wall cavity as "ductwork" and have a fan pull the air from the register, through the wall cavity and dump it into the basement.  Just block off the wall cavity above the register so the fan won't pull from the attic...or wherever.  This way, you will know for sure you will be getting the warmer air where you want it.

EDIT:  There are a number of factors that come into play for determining required air flow, but with 7,000 cubic feet of space, I would suggest something around 600 - 700 CFM...I may be wrong without knowing more about the space.


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## Troutchaser (Oct 21, 2010)

I can't go between studs.
I've got a guy coming out this weekend for a compressor install.  I'll get his two cents.

I do think that moving air between rooms via ductwork and in-line fans is a great idea to an age old problem.


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## bsa0021 (Oct 23, 2010)

[quote author="04RevX" date="1287620684"]http://www.smarthome.com/3011/6-In-110VAC-250CFM-In-Line-Duct-Fan-DB200/p.aspx

Here is what I have in mind.  I have a ranch and my wood stove is located at one end of the house.  In order to heat the rest of the house the room that the wood stove is in gets really hot.  I'm thinking of cutting in some duct work in the ceiling where the wood stove is located, run 6" diameter flexible aluminum ducting (and insulate it), install this fan at some point in the run, and dump it through the ceiling at the hallway at the other end of the house.  I just want to distribute the heat a little better.  Fans on the floor work but I hate the way they look.  I would throw this on a switch and flip it on and off when necessary.

I tried this 2 years ago in almost an identical configuration. Stove at one end of the ranch in which the room heats to 90 degrees at the cathedral ceiling. Cut hole in wall near the peak ran 20' insulated duct through attic and dump into room on other side of house using same fan you have. Unfortunatly, it does not work. You need a fan that moves at least 4 times more air. Someone suggested buying a large fan from someone like Granger and building a box and duct system similar to a furnace. Haven't had time to mess with it. Oh, i also tried reversing the fan to pull cold air to the stove room....same results. Those little fans work for boosting air flow in an exsisting ductwork that already has air movement.


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## Dune (Oct 23, 2010)

mayhem said:
			
		

> I've been considering doing something like this myself for a couple years now.  I was thinking of putting the ductwork so that I'm moving cold air out of the back bedrooms, through a duct and have it exhaust right behind the woodstove.  This should create a negtive pressure in the bedrooms and a positive pressure in the great room and thus force warm air down the hallway and into the bedrooms, right?
> 
> This has been beaten to death with the fan on the floor conversation, time and again we have all seen that its more effective to evacuate cold air out of the unheated room instead of trying to blow warm air around the house, right?  I suppose it would be easy enough to simply reverse the fan to reverse the airflow, right?
> 
> ...



Yes, this is the way to go. It is easier to pump cold air then warm air. Run the cold air duct in the cellar of the house. It does not need to be insulated. 

A hot air duct, even insulated, will lose a lot of heat in the attic. The air being dumped into the far room will not even feel warm.


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## Dune (Oct 23, 2010)

repost.


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## Dune (Oct 23, 2010)

fdegree said:
			
		

> I agree with Dan...trying to move cool air up and warm down is not likely to happen naturally.
> 
> Putting box fans on the floor is an entirely different situation.  What I'm going to discuss here is what seems to be the topic at hand...fans with ductwork attached.
> 
> ...




It is well established that option 2 works, while option 1 doesn't. 1 doesn't work because the delta T is too low.

Option 2 works for the reasons you mentioned, negative pressure in the far room, positive in the stove room, the path of least resistance is the "return", the open doorway through which the warm air passes, thereby following the laws of thermodynamics.


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