Please help. Needing to get better airflow from outside furnace

[jeremy_129]

Hey guys im new to this site and figured i could get some great advice from you all from what i've read so far. I just installed a free stove that my dad gave me and im having trouble getting good airflow into the house. The stove has to be 20 feet from the trailer, and have a building built around it. I'm using 10'' pipe untill i get underneath and then going to 8'' ( I was told this would make it blow harder into duct). It's hooked straight into my exisiting duct work. I have the fan wired to a thermostat so it'll kick off once it reached the right temp inside. The stove had a small blower on it and i replaced with a bigger one that was once used on a mobile home furnace. When i take the pipe off the top off the stop its got great airflow coming out of the top, but and the end of my pipe where i hooked into my exisiting duct theres not that much airflow. I figure im losing quite a bit of air at the elbow on the stove. I also don't have a cold air return, been told by several people i don't need one. I've used the stove for the past week and it's done ok but the fan has ran alot and its just now down to the 40's here. All i need is to get some better airflow and I feel like it will work alot better. Any suggestions? Thanks.

 

[jeremy_129]

Hey guys im new to this site and figured i could get some great advice from you all from what i've read so far. I just installed a free stove that my dad gave me and im having trouble getting good airflow into the house. The stove has to be 20 feet from the trailer, and have a building built around it. I'm using 10'' pipe untill i get underneath and then going to 8'' ( I was told this would make it blow harder into duct). It's hooked straight into my exisiting duct work. I have the fan wired to a thermostat so it'll kick off once it reached the right temp inside. The stove had a small blower on it and i replaced with a bigger one that was once used on a mobile home furnace. When i take the pipe off the top off the stop its got great airflow coming out of the top, but and the end of my pipe where i hooked into my exisiting duct theres not that much airflow. I figure im losing quite a bit of air at the elbow on the stove. I also don't have a cold air return, been told by several people i don't need one. I've used the stove for the past week and it's done ok but the fan has ran alot and its just now down to the 40's here. All i need is to get some better airflow and I feel like it will work alot better. Any suggestions? Thanks. Oh yeah don't laugh at the building im gonna paint it, i got the metal for $2 a sheet

 

[LLigetfa]

I also don't have a cold air return, been told by several people i don't need one.

Really? Isn't it like having just one wire on a battery? Try opening a window to create a "return".

Did you seal all the joints including the segments on the elbows?

 

[jeremy_129]

The building is not air tight so i figured that may help with not having a return. Everything but the elbow on the stove is tapped up with foil tape.

 

[Duetech]

Welcome to the forum Jeremy_129. When the blower is on are you getting warm air from your cold air return. Just hooking into your hot air plenum will not stop the heat from going into your cold air return. If your trailer is relatively air tight then you are going to have a problem getting sufficient air into the trailer. Test the air flow just before it goes in to the house to see if there is an obstruction or massive air leak. If you are losing air at every pipe joint you need to duct tape each joint. If you have connected to a small heat run instead of the main trunk line your problem may just be the size of the heat run is too small to handle the load and you need to connect the main trunk line/plenum. Even though you have been told you don't 'Need" cold air return on your set up it still sounds like you need to.

 

['bert]

I think he means open a window in the trailer. Otherwise you are trying to blow more air into a closed space. You have to let some cool air out to allow the warm air in.

Is this a common type of installation in your parts? Where I live that pipe will be under 4 - 6 ft of snow before Christmas. Opps, I mean the "holiday season" Don't want to offend anyone! :grrr:

 

[Gooserider]

Jeremy, welcome to the forums... You started two threads on essentially the same subject, which we like to discourage as it leads to confusion and duplication of replies as different people respond to the different threads...
Not a big deal, but it would be best if you could avoid doing this in the future...

I have used my "magic mod buttons" to merge the two threads together, and hope that will help get you a solution to your problem. Sounds like you've gotten some good advice so far...

Gooserider

 

[flyingcow]

If you hooked up your return to the trailer, you'll be reheating warmer air, than directly pulling it from the outside air. i don't know how cold it gets where you are, but it should be worth your time doing this. If you ever fix the air flow problem, you probably won't be able to get any warm air from you furnace in the cold months. Asking a lot of the furnace to heat air from 10 degrees to 70. It should balance the system out better also. Which will help with your air flow problem, hopefully.
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And it's my opinion that the blower on the furnace is not designed to push air that far, plus the bigger the round pipe, the less air flow you will have. Might be oversized for the application. I'd stay with the outlet size on the furnace, might have top go with an inch smaller to get the flow, maybe.. And you might have to put in an inline booster fan. You might be able to hook that up to the return pipe from the trailer. Keep it in the boiler room, hook it up to the same control that turns on the existing blower.

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Now, hooking this up to your existing duct work in your trailer, you may have the same problem of low/no flow in your dwelling. The ductwork in the trailer is probably going to be too big. Might be better off in trying to hook this up to its own register, in a common area(i.e. kitchen living room), if you did that I think you'd get good flow from the furnace. Than look to see if you need to put in a booster fan. Also keep in mind if you do this, you'll keep your common area warm, and also the t-stat that controls the rest of the trailer, which in turn will keep the other parts of house colder. But you'd figure how to tweak the system.
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See if you can find the original cfm's of blower unit this furnace came with, this will help with the problem. Also, when you get this performing the way you want it to, or the best it can. Buy some ductsealer, usually in a gallon can. seal up all the connections. basically just paint it on with a brush. Tape is a quick fix, but dries out quickly. As you might have guessed, I used to install HVAC systems(mainly commercial buildings), mainly the tin knockin' stuff. Never used duct tape to seal joints. Quite frankly never had any on the site. To use duct tape was the sign of a very poor installer, someone that I would relocate off my job site.
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Also, you'll need to insulate it, any F/G will loose it's R-value after the first rain storm. Might be an outside rated ductwrap, but I doubt it. Get everything else working properly, than tackle the insulation problem.

 

[jeremy_129]

Okay so it sounds like im gonna have to have a cold air return. What size pipe would you recommend using for the warm air? Coming off the top of the stove is 6''. If possible i'll use the 10'' pipe for my cold air. I really don't know much about the cold air return, will i just put a new register in the flow and then run the pipe from it to my blower? Hopefully i can get this working right within a week or so before it gets colder, I got all the time in the world though because i'm currently layed off. Thanks for the help guys.

 

[tbsdolmar]

You really should have a 12" pipe coming off of the top and a 12" hole in the stove for your supply. You also need at least a 14" pipe coming from the trailer to a box built over the fan for a cold air return. The return should be hooked to a separate register in the floor such as a 14x14 size or larger.

 

[flyingcow]

You really should have a 12" pipe coming off of the top and a 12" hole in the stove for your supply. You also need at least a 14" pipe coming from the trailer to a box built over the fan for a cold air return. The return should be hooked to a separate register in the floor such as a 14x14 size or larger.

Kinda curious how you came up with those sizes. If the unit has a 6 inch outlet, going bigger, if it isn't sized for it won't move the air properly. Just like the same problem he has now.

 

[tbsdolmar]

He said he put a larger blower on it so you have to have larger pipes for the amount of air going through it. I recently hooked up something similar for one of my customers using 12" pipe on both supply and return. It would have been better to use 14" on the return but he buried 12" pvc underground and it was expensive enough. You have to have a larger pipe for the return because a fan blows better than it can pull air. A trailer usually has 4"x14" duct in it and hooking toward the central part of the trailer helps make the flow more even.

 

[jeremy_129]

(broken link removed to http://cgi.ebay.com/10-Inch-Inline-Duct-Fan_W0QQitemZ360205519140QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item53ddec0924)

Anyone think this would help me out any?

 

[Blevesque]

6" Pipe is good for 100CFM
8" Pipe is good for 200CFM
10" Pipe is good for 350CFM
12" Pipe is good for 600CFM
14" Pipe is good for 900CFM
I'm not sure what the rest of the piping does but three elbows in the first 5' is driving your static up. Use the above figures and you should be close.

 

[Gooserider]

http://cgi.ebay.com/10-Inch-Inline-Duct-Fan_W0QQitemZ360205519140QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item53ddec0924

Anyone think this would help me out any?

It might, if you take care of some of the other issues like giving the air in the trailer an exit path...

Also as some have mentioned, the 90's in the line are not helping you any - in general 'bends are bad' and you want to make them as gentle and wide radius as possible - three 90's in close proximity is like putting a wall in front of your blower...

Gooserider

 

[jeremy_129]

Ok thanks for more great advice. I think i'm gonna install a cold air return this week. Where should i put the register inside for the cold air return?

 

[Gooserider]

Since you said you were putting the furnace output into your existing supply ductwork, I would think the best thing to do would be to tie into the existing return plenum if you have one... That way you take full advantage of the existing ductwork to spread the heat around. If there isn't a return plenum as such, I'd consider doing a low mount wall or floor return in the same general area as the intake for the existing furnace...

Gooserider

 

[jeremy_129]

Hey guys i've been working on the stove and gotten it to do a little better, it's been going 24/7 since November 1st. I got rid of the 90's, had to cap the top off and cut hole into side of stove (it's double wall). I've also installed the cold air return. Good heat comes out of my vents just now as much airflow as i'd like. If I can get the airflow better then the fan will not run as much, so i've been looking into buying an inline fan and stick it somewhere in the duct to help out my other fan. Tell me what you think of this fan, thanks.
(broken link removed to http://www.aftproducts.com/Duplicate-of-Duplicate-of-Duplic.item)

 

[Gooserider]

Hey guys i've been working on the stove and gotten it to do a little better, it's been going 24/7 since November 1st. I got rid of the 90's, had to cap the top off and cut hole into side of stove (it's double wall). I've also installed the cold air return. Good heat comes out of my vents just now as much airflow as i'd like. If I can get the airflow better then the fan will not run as much, so i've been looking into buying an inline fan and stick it somewhere in the duct to help out my other fan. Tell me what you think of this fan, thanks.
(broken link removed to http://www.aftproducts.com/Duplicate-of-Duplicate-of-Duplic.item)

Looks fairly typical for an inline fan - I don't see anything "wrong" with it, or anything to really rave about either... The one issue that I would see is that it's for an 8" pipe, but in your first posts you said that most of your supply duct was 10"... You should get an inline fan that is at least as big as the duct, never smaller....

Gooserider

 

[benjamin]

I wouldn't bother with any sort of fan. I'm assuming the blower you have is a typical furnace blower, not a fan that some mobile home furnaces have. The blower is designed to operate under conditions that range from modest resistance to airflow to almost complete blockage of airflow. It actually spins easier the more blocked it is, and is more heavily loaded if it has too free of air movement.

So if you have a blower hooked up to a long length of small diameter duct with lots of elbows it will produce a pressure so high that an inline fan probably won't help you much. If you shorten the run, increase the diameter, reduce the number of elbows the fan may help, but the blower won't need the help then.

Sounds like you're close to getting it to work the way you want it. If not then consider the above suggestions.

I agree that a return is the first priority.