Inline duct fan wiring...

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Old 10-29-19, 04:37 AM
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Inline duct fan wiring...

Hello, longtime reader, first time poster. Just bought a log cabin with a 2 bay garage under it. Oil furnace, forced hot air. Turned garage into bedroom for daughters, had to run 6" flex hose. Not enough hot air comes out (no big surprise, with the flex line) so I bought three inline duct fans to push more heat to my cold daughters. The fans have a plug on the end of the wire to plug into an outlet. I'd like to have the outlet turn on when the blower motor in the furnace turns on. I'm thinking a sail switch, but I'm sure there are better ways to do it. Any help would be appreciated.
 
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Old 10-29-19, 05:53 AM
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It might be possible to wire the outlet directly to the motor blower in the furnace, but I don't know if that would take power away from the blower motor, or if you would need some kind of a relay switch...
 
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Old 10-29-19, 08:41 AM
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Quick numbers with just guessing at info. Probably need more like 3 8in ducts and that is on the low side. I used 22x20 as garage size. Have no idea on location, insulation, windows, garage doors etc. All will play a part
 
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Old 10-29-19, 10:39 AM
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Hi, thanks for your reply. 22x20 is correct. R-19 in walls, r-38 in ceiling. Western ma. I can't change the duct sizes, as the ceiling is sheetrocked and there is absolutely no room within the floor joists above to house anything larger than what I have. It is what it is, at this point. But I do want to increase warm air flow into the room with the inline duct fans.
 
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Old 10-29-19, 11:55 AM
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Don't think the fans are going to help much. Just can't move enough air through the flex duct. 6 in flex can only handle about 60 cfm (best practice). Duct fans rarely work. Hope you get lucky for your kids sake.
 
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Old 10-29-19, 01:09 PM
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Well if the booster fans don't do it, we'll have to look into electric baseboard. I sure hope someone can help with the wiring though. Going to be cold this weekend
 
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Old 10-29-19, 06:20 PM
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Did you try the fans first to see if remote powering is worth the effort ?
Just plug them while the heat is running to see if they'll do the job.

I don't know many people that were satisfied using those duct boosters.
The furnace is not setup to supply remote switched 120v.

I have wired setups for customers as well as guiding members here. In the picture is a 4" square 1900 box. You can put a plate on it with two duplex receptacles giving you four places to plug in. The cord to the right is a three wire power cord that plugs in and supplies power to the box. The relay on the top gets 24vAC from the furnace/thermostat on a request for the fan to run. The relay is an RIB relay. Seen in link below.

I can help you wire it if you want to go that route.

RIB relay
 
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Old 10-30-19, 07:12 AM
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PJ, I sent you a private message. Also, I can't view the image you posted, it comes up with something about how this site only attaches photos and does not... I don't know, some kind of HTML jargon
 
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Old 11-01-19, 07:44 AM
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PJ, haven't heard back from you, hope all is ok.
 
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Old 11-02-19, 09:46 AM
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I highly doubt that an inline fan will be of much use.
A two bay car garage is a huge amount of space and there is a slim chance your existing furnace can even handle it.
A booster fan sometimes works on existing ductwork with the intent of adding a small amount of additional heat, like to an existing bathroom or bedroom.

You need to add more heat and electric baseboards are the least expensive to install.

More detailed info on your cabin and heating system would help
 
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Old 11-02-19, 12:03 PM
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Well... In the basement we have the oil-fired forced hot air furnace, and on the other side of the room we have a wood furnace. The wood furnace has a stronger blower motor than our hot air furnace does.
 
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Old 11-02-19, 08:54 PM
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How did you decide 6” flex was big enough? And what about a return air duct?
 
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Old 11-03-19, 01:15 AM
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Need more info on how this building is laid out.
You said it has a garage under it and now also state that there is a basement

As roughneck 77 said a cold air return should help.
You need air circulation.

Also are you going to leave the heat on all winter?
 
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Old 11-03-19, 03:08 AM
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The layout is like this-the front was the 2 car garage, the rear was/is basement where the furnaces are. Yes, the heat will have to be on all winter. 6" hose is the biggest that will fit in the joists. I ran 3 of them, one down each sides and one down the center. I did put a return, so there is air circulation. Just not enough heat. Yet.
 
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Old 11-03-19, 03:49 AM
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You’ll likely have to upsize the duct.
If you do try and force air through, the airflow is likely to be noisy.
What size return did you run?
 
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Old 11-03-19, 04:02 AM
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When you add a duct to an existing system you are robbing heating capacity from the rest of the house.
You can add a booster fan which will have a similar effect to upsizing the duct.

A similar effect can be had by partially closing all the vents in the rest of the house which would increase plenum pressue forcing more air into the new duct.
 
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Old 11-03-19, 06:55 AM
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I have already turned down the rest of the ducts in the house, closed them off. I can't put anything bigger for a supply line in there because nothing bigger will fit. I'm kind of stuck with what I've got.
 
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Old 11-03-19, 07:08 AM
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Sorry to say but what you’ve got probably isn’t going to work, fans or no fans.
There’s simply not enough air in or out to satisfy the needs of the rooms.
How large are the rooms and what insulation value was used?
Closing off the other supplies can cause other problems, even damage to the furnace.
 
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Old 11-03-19, 07:12 AM
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I think I included a picture... It is of the weird joist system... It is basically 2x4s with a truss system, like rafter trusses. They do not line up, and are irratic so that there are no Chanel's per se, I had to go back and forth quite a bit which I'm sure cut down the airflow immensely.
 
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Old 11-03-19, 07:15 AM
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The room is about 17 by 22. I have r 19 in the walls, r38 in the ceiling, because this used to be an unheated garage below our living room.
 
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Old 11-03-19, 07:20 AM
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That’s a huge problem.
Not only is the duct likely undersized, but it’s squished.
There’s no chance of making that work no matter how big of a fan you put in the duct.
You’ll have to find a way to put a continuous duct, of the correct size, all the way from the takeoff to the bedrooms.
First, I’d do an individual room manual J with a manual D to figure out what kind of airflow the rooms need in the first place.
 
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Old 11-03-19, 09:04 AM
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Another problem you will face is that you will get a small amount of warm air into the new space with your plan but being a single zone the rest of the house will satisfy the thermostat long before the new space is warmed up.

Like I said, that space is really too big for what you are trying to do.
Electric supplemental is the way to go.
There are different electric heating options that could be better for you than baseboard.
 
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Old 11-03-19, 11:39 AM
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What other electrical options are we talking about?
 
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Old 11-03-19, 11:49 AM
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Could put in a minisplit heat pump for the bedrooms.
 
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Old 11-03-19, 03:04 PM
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I'll look into it. I think I've seen minisplits on ebay
 
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Old 11-03-19, 03:11 PM
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Avoid some of those cheap online brands. They don’t work well, offer limited to no support and don’t offer much in terms of technical information.
Mitsubishi and Samsung are my preferred.
 
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Old 11-04-19, 04:51 AM
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The ductwork I've run goes from the furnace plenum to the far wall of the bedroom, which is the outside wall, front of the house... What if I run a couple to the inside wall? There is a return on the inside wall.
 
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Old 11-04-19, 05:36 AM
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Supplies should be against outside walls. If the supply and return are both against an inside wall, there will be a huge temperature contrast across the room.
Plus you still have the issue with crushed ductwork that’s of inadequate size.
 
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Old 11-05-19, 04:08 AM
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You have been given advice from folks who have experience in this area that adding duct work to your furnace may not be the best way to heat this new space.

Honestly, we really should really put the brakes on this because you haven't offered any info on the specifics of house size, garage sq footage, insulation level and window type, floor type and insulation value and most importantly your approximate location.
There are too many ones and zeros being wasted by pure speculation.

Info and pics would maybe let us give you some solid, accurate info.
 
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Old 11-05-19, 04:30 AM
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If you are in an area that sees freezing temps you are going to need a Mitsubishi M series unit. All others just don't heat as good. Some are 100% capacity to under -5.
 
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Old 11-05-19, 06:11 AM
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But... I've shared that it is a log cabin, the garage / new bedroom is 22 by 20, there is r38 in the ceiling of said new bedroom, r19 in the walls, and r7 in the floor. The log cabin is about 1,200 square feet...I put two windows which are 42 by 50 and one door in the new bedroom on the exterior most wall, farthest away from the heat source.any other information I can find if I don't know it. I don't know what the r value is of 6 inch of wood for the log cabin itself... And I do not know what is in the vaulted ceiling for insulation. I would guess r 30 or better. It was built in 1995. The furnace itself is a rheem.my location is in western Mass, where it frequently drops below zero in the winter. The floor was concrete, but I put pressure-treated ribs down, foam board insulation in between them and plywood and then padding and rug in the new bedroom. The windows I put in our insulated double pane glass windows... They cranked out and open like French doors. The door is your standard home Depot aluminum-clad foam exterior door.I should be home in a few hours, I will take pictures of everything for you guys. Actually, I might have some here on my phone... Let me see if I can do this
 

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Old 11-05-19, 06:22 AM
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Pictures

Nope I don't think I can do it from here. I will try again when I get home in a few hours
 
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Old 11-05-19, 08:09 AM
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Pictures of garage/bedroom and cabin
 
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Old 11-05-19, 08:21 AM
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First thing I’d do is run a manual J on each room to figure out your heat load, then a manual D to figure out what kind of airflow you’d need.
Just a wild guess but I figure you’d need at least continuous 10” supplies to those rooms.
Likely a larger return.
 
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Old 11-05-19, 08:40 AM
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It's just one room. The girls share the bedroom.
 
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Old 11-05-19, 09:01 AM
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Just need a single room manual J done then.

www.loadcalc.net
 
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Old 11-05-19, 09:02 AM
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This is probably a stupid question but why if the new room backs onto the furnace room are you going up through the floor trusses?
Why not go through the common wall?
 
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Old 11-05-19, 09:14 AM
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The common wall is the inside most wall. I have to heat the three outer walls. There is no wall running down the middle of the old garage, it is one big open room
 
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Old 11-05-19, 09:42 AM
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Old 11-05-19, 10:28 AM
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That’s just the indoor head. It will need an outdoor unit to go with it.
 
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