# Aprilaire 700 install location



## Ericfox (Dec 10, 2016)

Hey everyone,

New member here. I just purchased an Aprilaire 700 humidifier for our home and hope to get some guidance on where to install in the ductwork. 

The directions say the supply side vertical duct is the preferred location. It says you CAN install in the return side if you have to... but I'm not sure if this is a desirable location? Is there any concern about messing up our air filter? It is an Aprilaire filter that I change 1x per year per the directions. Maybe the return is not as effective due to the cooler air? 

Attached are some pictures of any spot the template would fit. 

I dont know much about ductwork construction - so I am guessing most of the proposed locations won't work. Any help is much appreciated! 

Thanks! Eric


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## raylo32 (Nov 25, 2006)

Not a pro but I installed my 700 maybe 8 to 10 years ago and it's still going strong. Yes you get better evaporation on the warm side and that is how mine is installed, in the plenum just above the A-coil in my upflow furnace configuration. The pros here generally recommend installing most humidifiers on the cold return side so in case you get a leak the circuit board and blower should not be affected. But I think that makes more sense for the bypass types and not so much for the 700 series. The other thing you can do no matter where you install it is to use hot water to feed it. The heat aids evaporation and most of the heat is pulled out of the water before it drains off. Using hot water would be more important if you install the 700 on the return side.


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## user_12345a (Nov 23, 2014)

Which side you put it on doesn't make a difference.

Either way, warm air is going to pass through the pad, air flows from high pressure area to low pressure area. from the supply, through the humidifier and back to the return.

put it on the return. if the humidifier leaks and is on the supply side it can wreck the furnace.


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## raylo32 (Nov 25, 2006)

No, the 700s are not bypass units. They pull the air out, across the water panel, then return it to the same duct with a self contained 120vac fan. The instructions say to install on the supply side.



user_12345a said:


> Which side you put it on doesn't make a difference.
> 
> Either way, warm air is going to pass through the pad, air flows from high pressure area to low pressure area. from the supply, through the humidifier and back to the return.
> 
> put it on the return. if the humidifier leaks and is on the supply side it can wreck the furnace.


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## raylo32 (Nov 25, 2006)

Looking at your pics I would probably rotate the water heater expansion tank out of the way and put the humidifier on the duct there. You could put it where you show it barely fits but it will be easier to service in the lower location.

Plus I believe the risk of leaks causing furnace damage with this type of humidifier is very low. The only water inside the unit is low pressure draining over the water panel and the drain opening is very large as compared to the ~8gph flow. I can't see any credible way for mine to clog. You could of course get an external leak on the supply line or solenoid valve but that wouldn't hurt the furnace... might ruin other stuff in the room and the floor but you have this risk no matter what type of humidifier and no matter where you install it.


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## supers05 (May 23, 2015)

The location is a bit more flexible. If you look at the back panel, the actual holes don't have to be as big as the template. You might just need a bit more foil back tape to seal were the plastic isn't flush with the metal. 

Cheers!


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## Ericfox (Dec 10, 2016)

Thanks guys! I think I'll mount it somewhere on expansion tank side. Tomorrow's the day!


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## Dog5 (Jan 3, 2011)

We have one of these and it's been great. 

Ours is on the supply duct (which I would recommend) and I decided to feed it with cold water to save money and see if it was good enough. It brings the relative humidity up to the point where it gets rid of static, dry throats and cracking skin on the hands. That's with the control/sensor (mounted on the R/A) turned all the way up. I didn't bother with the outdoor sensor since the windows never get fogged. 

A lot of water does go down the drain. It would be interesting to measure the difference in temperature of the water leaving the unit compared to going in.


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## raylo32 (Nov 25, 2006)

I don't think using hot water really costs much if any more since most of the heat comes out of it in the process. I didn't measure the temp of the water coming out with a thermometer but it is cool to the touch on mine with 130 degrees going in. The water flow rate is about 8 gallons per hour. It is probably higher than it needs to be and will bump up your water bill. I wish they made a replacement orifice that flowed less. I do see they make a lower flow bypass unit but I don't think they make a 700 series version (yet?).

For the OP think about where you send the drain water. If you use you air conditioner condensate line out the house you'll end up with a skating rink where it exits the house. Alternatively you can use a condensate pump and send it to a utility sink drain... or do like I did put a loop in the drain line for a trap and tee it into a cleanout cap in the main drain stack so it just goes out to the sewer line.




Dog5 said:


> We have one of these and it's been great.
> 
> Ours is on the supply duct (which I would recommend) and I decided to feed it with cold water to save money and see if it was good enough. It brings the relative humidity up to the point where it gets rid of static, dry throats and cracking skin on the hands. That's with the control/sensor (mounted on the R/A) turned all the way up. I didn't bother with the outdoor sensor since the windows never get fogged.
> 
> A lot of water does go down the drain. It would be interesting to measure the difference in temperature of the water leaving the unit compared to going in.


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## Ericfox (Dec 10, 2016)

I tied into the air conditioning condensate line- but it goes right into floor drain in the basement. So far it's working great! Here's a pic


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## Ericfox (Dec 10, 2016)

I used an add-a-line slip on assembly instead of the saddle valve that came with the humidifier


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## supers05 (May 23, 2015)

Ericfox said:


> I used an add-a-line slip on assembly instead of the saddle valve that came with the humidifier


Looks good. The slip ons are better then the saddle valves anyways. At least you can turn it off some time in the future. 

Cheers!


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## raylo32 (Nov 25, 2006)

Looks good Eric, enjoy! I think you'll like it.


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## Dog5 (Jan 3, 2011)

Ericfox said:


> I tied into the air conditioning condensate line- but it goes right into floor drain in the basement. So far it's working great! Here's a pic


I think you made the right decision on where to put it even though you had to span a cleat connection. So how did you deal with cutting the cleat?


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## Ericfox (Dec 10, 2016)

Angle grinder with cutoff wheel worked- and I cut the front part of the cleat off where the humidifier overlapped (just a tiny little piece about 1/4"X1")....if that makes sense


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## supers05 (May 23, 2015)

Ericfox said:


> Angle grinder with cutoff wheel worked- and I cut the front part of the cleat off where the humidifier overlapped (just a tiny little piece about 1/4"X1")....if that makes sense


Ah, sounds like you're an hvac man now. Lol. 

Make sure that the humidifier is more then 6" away from hot water tank venting. If it's not, use some sheet metal as a shield to protect the plastic, hanging in between. The left overs will work just fine. 



Cheers!


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## Ericfox (Dec 10, 2016)

Nah... HVAC hack 

Thanks for the heads up on the vent. It is deceiving in the pic. It's a good 12" away at least


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## MartyEast (Jan 22, 2021)

Ericfox said:


> I used an add-a-line slip on assembly instead of the saddle valve that came with the humidifier


Can you post a up close photo of the slip connection? thanks


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