Step 7: Hook Ups and Testing

Using a large drill bit, drill a hole in the side of the furnace where the armored cable will come through.

A step drill bit will come in handy but you can do this with a dremel tool. I highly recommend the step bit. You can probably find one for less than $15, don't go nuts on specially coated step bits, just get something to finish the job.

At this point, it is a matter of hooking everything up.

Identify the connection points on the board, run the wires to the relay and connect everything up.

Check, double check and triple check your connection. You don't want to fry the controller board just because you made a "small" mistake like hooking L1 to Common in effect creating ashort.

For all other connection not using a disconnect terminal just usethe striped wire end and marrette technique explained in Step 5.

I should touch on how to cut the armor. Look at the picture. You will see that I bent the cable and as a result, the armor just "snapped" out. Using wire cutters (side/diagonal cutters) cut the metal strip. Be careful not to cut the wires or the insulation. This sounds complicated but believe me, once you bend the cable you will see what needs to be done.
After you cut the armor, trim the cut end so it doesn't slice the insulation and pull it out.
Run the end in the junction box and secure it with the clamp.

If you are not installing an enable/disable switch then you don't need the armored cable. In this case the 14-2 will go into the box.

If you are installing the switch then run the other end of the armored cable to the box where the switch is and make the necessary connections. Remember, the black wire will be connected to the switch, the white one will be connected to the 14-2 cable and the bare wires will be connected together and hooked up to box.

The pictures below will show where things are and what you need to do.


When all connections are done, restore power to the furnace, crank up the heat on the thermostat, if you used a enable/disable switch make sure it is in the ON position and either push the interlock switch or tape it (don't forget to remove the tape when done).

At this point, after the blower motor kicks in you should hear the relay being energized (one click). Go to the register and inspect for higher air flow. At the thermostat either turn down the setting or just use the OFF position to turn off the furnace, when everything is off (there will be a delay) inspect the register again to make sure the fan is not on anymore.

<p>do they make inline flow switches? My ac unit is down stairs and to hard to run a power cord to. I do have power upstairs which a flow switch could be powered from.</p>
<p>Actually it all works out better for me that way. I can now plug the booster fan power supply into a 24 hour wall timer. The booster fan is for a room that is only occupied at night. This is a good option for others who want to do it like that.</p><p> I had everything wired and install only to find out I had a defective relay. I do not know if yours does the same but this relay whine so loud when energize, you can hear it from the floor above. I recheck the connection and everything was correct. I am going to get another and if it still does the same I might have to relocate it to inside the furnace like you did yours.</p><p>Thanks again.</p>
Thanks Elton. Use the relay as a switch, when the relay is energized, it will close the circuit regardless of where the power is coming from.<br>You should try to do the total amps to see if you are still within 15A. The furnace should have some sort of label giving you the total current consumption.
<p>Raptor, my booster fan is only 0.7A but I have a powered humidifier and a EAC unit hook up to the board already. My furnace main blower is 1 HP (don't know the amp). I was thinking that's a lot going on in there already so I would prefer to have an outside source to powered the booster fan if possible. I just need the furnace to trigger it when the main blower comes on. </p><p> I ask cos in your write up you said, &quot; Make sure your L1 is not powered when your furnace is off &quot;. So, if my booster supply line is from an outside source instead of the L1, the line will always be powered regardless if the furnace is on or off. Just wasn't sure if the relay can be connected like that. Don't want to toast anything.</p><p>BTW the supply line for my furnace is 15A ( max per GDM installation guide ). Thank you for your good write up.</p>
Hi Elton, I'm not sure what the EAC is but if has power when the heat and cold is on then you can use it to activate the relay.<br>If you are concerned about the power drown by the booster you can source the power from a separate outlet, etc. my booster is not that powerful and the board looks like I'm t can handle the juice required to power it.<br>Take a look at the label and see what the power is, it my be listed as watts, e.g. 0.25W or the current it pulls, e.g. 0.5A. Your furnace is most likely on its own circuit of 20A or 30A, that's a lot o power to go around for the furnace a a small motor in the booster.<br><br>You should still check to make sure everything is ok, don't just take my word for it.<br><br>Feel free to post questions/comments here. I'll do my best help out.
<p>Can I connect relay to EAC instead of HUM terminal? This way it will be energized on both HEAT or COOL when the blower comes on. </p><p>And the power source for the booster fan, does it have to be from the furnace board ( L1 in your case ) or can it be supplied from an outside 120v line. I ask because during heating the furnace is pulling a lot of load running main blower, induce draft blower, humidified, EAC etc...all through control board line. Will it be too much to add a booster fan to it.</p>
<p>Due to location in sub attic running control wire to relay would be a major task. Any bright ideas on sensor that I could attach to a relay that would sense airflow in duct? </p>
Can you connect the duct blower straight to the hvac blower?
<p>You could. The reason I didn't do it was because I wanted to have complete isolation between the control board and my booster fan via the relay, I didn't hook it up to the blower because I was not sure how the blower and the relay would behave if both were energized from the same source.</p><p>Apparently, most control boards have a dedicated output that is on when the blower is on. I forget what is called. I might have mentioned it in one of my previous comments.</p>
I agree, Bill. When I did this, I couldn't figure out which terminal was the one for blower, hence the heat only option. I think in one of my comments I mentioned which terminal to use. Even if the booster fan comes on early, it is not a problem. It's not on for too long and it doesn't temperature. Maybe at some point when I have some spare time I'll do it right, that way, it will kick in when the AC is on as well.
Great write up! A couple of comments. As for picking up the relay control from the thermostat, your booster fan will come on when the tstat calls for heat. Not when the furnace finally warms up and is ready to deliver heat. Thats why the blower does not spin up right away. It takes time for the furnace to get hot. Otherwise the blower would be moving cold air. As for changing the fan speed with a dimmer, it might work to sme extent, but not properly, and will drastically reduce motor life. Motor speed on these is based on the frequency of the ac power coming in. Due to the laws of nature, reducing the voltage will just increase the current, and will overheat the motor windings and maybe your control relays and wiring.
Thanks for the great guide on installing the booster fan ( something I'm considering ). The only question I have is around your relay wiring. Did you consider using the R and G thermostat wires with a low voltage relay? It would seem to be easier to pickup the thermostat's request for the fan regardless of heating or cooling... <br> <br>Also how to you find the noise? Did you need to insulate around it at all?
I'm not sure how the thermostat interacts with the control board using those two wires. Maybe and HVAC guy/gal can help here. I was concerned that my adding a relay in that particular circuit might mess something up. If you look into it and it turns out it is a better option, please do share the info here. I know there is another output on the board that would power the relay regardless of setting (cold/heat) - I forget what it is called now. The other thing is that the thermostat, tells the board when the threshold has been reached/crossed but the board really turns the blower fan off a little while later to fully take advantage of any hot/cold air left in the system. <br>Personally, I'd still use the control board to turn on the buster fan. <br> <br>The noise level is a little higher than what I want it to be but I got used to it. I am talking about the noise coming from the register. There is almost no noise where the buster fan is installed. <br>I can't tell is the register noise is high because of the increased airflow (I'm sure that is a factor too) or because of the noise coming from the motor through the ducts. I guess, if you want to eliminate any telegraphed noise, you could use some rubber connects (Home Depot sells them) to connect the motor to the ducts and avoid any motor noise or vibration. <br> <br>One of these days, I'll measure the noise level and post it here. If I had to guess, I'd say it is twice as loud as an old fridge, not as loud as a regular dishwasher though. <br> <br>I hope this info helps. Let us know what you find out about the R &amp; G wires.
Just in time as I'm working on something similar. I've laid out my ducting with the booster fan and looking how to turn it on when heat/cool is called. So, just to clarify, the GREEN wire &amp; WHITE (common) wire can actually energize a 24VAC relay to switch ON the booster fan? I've just inspected my thermostat's wiring and notice that the common wire is not connected (but present). Is common wire normally not connected with these digital thermostats?
I bought exactly the same duct booster. The only problem I have with the unit is the noise. I'm considering installing a dimmer switch in the power run instead of a normal switch to see if there is a good trade off between noise and air flow. 250 cu ft per minute is a lot of air flow considering I'm heating a room of about 1200 cu foot. Thanks for the instructions.
That is a great idea. Be careful not to turn the dimmer all the way down. If the coils in the motor don't get enough juice to turn, you might short them.
Sorry for the delayed post. I finished wiring the fan using a 24VAC relay and the GRN (fan relay) and C(Common) leads from my thermostat. I did the actual wiring in the air handler since the duct and installed fan were located nearby. I installed the duct fan relay in a box near the fan. I pulled 120VAC from a nearby crawl space outlet. This serves a sun room that is at the end of the trunk. The thermostat gets it power from the 24v transformer in the air handler. The thermostat gets power from the transformer (the batteries are for programming backup and screen lights) and when the set temp calls for heat or cool a relay in the thermostat activates sending 24VAC via the GRN wire to the air handler fan relay. I connected the 24VAC duct relay to the GRN and C so that when the thermostat called for fan the duct fan would also activate. BTW, I have a single speed heat pump fan. This has been working great for me and the temperature in the sun room is tolerable. I got the 24 VAC relay from amazon. I included a scan of a thermostat schematic but it may not be readable. If you Google aprilaire 8346 thermostat wiring and look at page 9 of the pdf you will see what I tried to explain.
Cool, thanks for the update.
Great instruction! Dont know if it was mentioned anywhere but I plan on installing the fan using a 24 VAC relay energized by the GRN fan relay from the thermostat switching the 120 VAC for the fan.
Hmmm, I'm not sure how that is going to work out. I have a digital thermostat powered by 3 (I think) AA batteries. Energizing the replay from those batteries would drain them quickly. <br>I don't know enough about the thermostat and the control board from the furnace/AC communicate. From your comment, it sounds like there is power control on a 24V circuit coming from the thermostat. <br> <br>Please post some details, it might simplify my solution and make the idea more appealing to people who are not comfortable &quot;tapping&quot; into the furnace/AC control board.
The reason for two speeds is that it is not difficult to get warm air to rise up to the upper rooms so a low speed will work normally. <br> <br>Cold air from the AC is denser and not so easy to lift to upper rooms. Thus the higher fan speed
How greatly has that improved the temperature in your room?<br />
I checked the temperature last night with a digital thermometer (point and shot type) and it was ~106F/41C which is up about 30-40% from when I didn't have the fan. The air flow is almost 100% increase.<br /> I compared the temperature to two other registers, one very close to the furnace and one a little closer to the furnace than the register in our bedroom. Here are the readings for the two:<br /> - register very close to furnace: 122F/50C<br /> - the other register 90F/32C<br /> <br /> The last register (90F/32C) should be warmer than the one in our bedroom given that it is a shorter length and does not go through the space between the garage ceiling and bedroom floor.<br /> <br /> I will update the Instructable with info re. performance.<br />
I have the exact situation as you had with a cold bedroom above a garage. <br>I would like to add one of these booster fans to the heat duct as well as to the cold air return duct. ( I added a cold air return as there was none previously. However the pull is very weak). <br> <br>Is it possible to connect both to the fan blower? <br>Thanks.
The short answer is no. The two air pathways are separate plus you can't change the direction on the motors on demand. When you mount them you make sure they pull or push based on your needs.<br>It sounds like you will have to use a separate blower for the cold air return but have both blowers turned on and off by the same relay.<br><br>I'm not sure you really need one for the cold air return. I suggest you talk to and HVAC guy and see what he says.<br>Maybe other people here can shed some light on this.
Yes, I was going to use two booster fans. One for the heat duct, one for the cold air return. I guess I could use a pressure switch for the heat duct fan, and wire the one in the cold air return to the main furnace blower.<br><br>The cold air return that I added barely pulls at all, so it needs something to increase suction. Thats why I was thinking of a booster fan, in reverse.
Make sure you use a relay. That way you keep the two circuits separated electrically and avoid liability to a certain extent.
HI F22-Raptor,<br /> <br /> Where on earth, but more specifically in the GTA, can a mere mortal purchase the relay you used for this project? Or its equivalent?<br /> <br /> Eastern Refrigeration won't sell it to me because I'm not an HVAC tradesman.<br /> WWG Totaline won't sell it to me for the same reason.<br /> Seriously, I'm standing there looking at it, cash in hand, and...no sale. I couldn't even grease the guy. I'm assuming it's not some critical component in a nuclear device, so what's the problem I wonder.<br /> <br /> Ebay sellers want US$30 just to ship it to me so I'm trying to avoid that route. Certainly someone in the GTA can supply this to a DIYer.<br /> <br /> I've also tried Westburne-Ruddy, Nedco, and TES. No luck.<br /> <br /> Thanks for any help. Other than the relay, I'm ready to go.<br /> <br /> <br />
That is really strange. It's just a relay. When I got mine form Eastern Refrigeration I just walked in, told the guy I was looking for a relay and he got one for me.<br /> Your best bet would be to go to Sayal (<a href="http://www.sayal.com" rel="nofollow">http://www.sayal.com</a>) and go to their relay section. I got 3 relays from the Matheson Blvd. and Dixie Rd. store for about $7-8 about 3 week ago. They have lots of them. Your biggest problem will be finding the one you want. They have one aisle just for relays 5V, 6V, 12V, 115V, 240V etc. They also have solid state relays but they are more expensive and for this kind of application it doesn't make sense to use them. While you are at Sayal look for quick connect terminals, shrink tubing etc. You should buy 2 relays (heat and cold) and be done with it. When I did mine I wasn't sure how the whole thing was going to work out. Next year I'll do the cold relay as well.<br /> Let me know if you need help, I work 10 mins from Matheson and Dixie.<br /> Sayal has a store in Vaughan as well (check out their locations on their site), that one is 10 mins from where I live.<br />
&nbsp;Just curious, but why did you use a relay?<br /> <br /> Couldn't you just drive the booster fan from the HUM connection point? Isn't it only energized with 115V when the blower motor is on?<br /> <br />
That's a great question. It's something I should've covered in the Instructable. There are two reasons:<br /> 1. My controller has separate outputs for Heat and Cold and from what I'd read it sounded like there are separate windings in the blower motor (2 different speeds I guess). Later on, this will allow me to install a second relay that will be energized by the Cold circuit, that way, my fan will kick in when the AC is on as well.<br /> 2. Liability, if my fan is totally separated from the control board via a relay, then I don't have to worry about it damaging the control board if something happens on the fan side.<br /> <br /> Also, the relay option will allow other people to control fans that are not 115V, say 24V. Obviously they will have to use a separate transformer or use the one that's already in the furnace but from a control point of view, using the relay keeps things segregated and safe.<br />

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