# Hot water line to the furnace humidifier?



## 1750

I needed to replace the crumbling humidifier pad on the Aprilaire unit bolted to our new NG furnace.   I noticed the water line for the humidifier taps a hot water and not a cold line.  This was a surprise to me. 

This results in a trickle of hot water running through the unit and out the drain on the bottom whenever it's on.   Is there a reason this should be hot vs cold water?   If not, it would seem to make sense to move it over and tap the cold line.

Thanks for your thoughts on this!

Mike


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## woodgeek

swap it.  somebody either made a mistake or had a 'bright idea'.


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## 1750

woodgeek said:


> swap it.  somebody either made a mistake or had a 'bright idea'.


Thanks, WG.   After I posted this, I found this from the Aprilaire site:

*Should our Aprilaire humidifier be connected with hot or cold water?*
Aprilaire evaporative humidifiers can operate with hot, cold, hard or soft water. Hot water is preferred as it supplements the heat from the HVAC system heat call to increase the evaporation rate. All Aprilaire humidifiers need some source of heat for evaporation to take place whether it is hot water or hot air. When the humidifier is wired to operate on a heat or HVAC fan call, hot water is required as it is the only heat source for the evaporation process during an HVAC fan call. In addition hot water is required when the humidifier is connected to a heat pump. This is due to the lower plenum temperature in a heat pump. Hot water ensures there is an adequate heat source for the evaporation process. When any drain-though Aprilaire Humidifier is connected to hot water, the heat in the water is used in the evaporation process and the water coming out of the drain will be cool to the touch.  

Does this make sense?


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## Highbeam

They seem to be saying that hot water will evaporate easier and faster. I propose that cold water will also evaporate but at a lower rate.


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## woodgeek

Learn something new every day.  

But I agree with Highbeam, who needs that much vapor?


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## DougA

I would think that by the time the hot water trickles through, it is no longer hot but cool.  If you change it to a cold water pipe and add a few extra feet that you can loop near the furnace, the water will be about the same temps but without costing so much. 
Have to agree that if you have hard water and softened hot water, I'd leave it alone. The time and effort to unplug a humidifier that is full of guck from hard water is more than the cost of the hot water. Pretty rare to see one soft & one hard but my parents had that in their home.


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## 1750

I just checked the temp of the water coming out of the drain pipe and it's really cold.   The vaporization really pulls the heat out of it!  

It would be interesting to know how much water is actually being used across the course of the day.


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## sloeffle

1750 said:


> I just checked the temp of the water coming out of the drain pipe and it's really cold.   The vaporization really pulls the heat out of it!
> 
> It would be interesting to know how much water is actually being used across the course of the day.


I was looking at one of the newer drainless units and they say it can put up to 16 or 18 gallons of water into the air everyday. It looks like it depends on the model that you have:

http://docs.electronicaircleaners.com/aprilaire_humidifier_selection.pdf

Based on the model, and furnace usage. You could theoretically use up to 144 gallons of water a day. 

I balked at the idea of installing one after hearing too many stories of rusted HVAC ductwork and flooded basements.

Scott


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## woodgeek

For reference, after airsealing, I need <5 gallons a day to maintain 35%RH even during arctic weather.


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## sloeffle

woodgeek said:


> For reference, after airsealing, I need <5 gallons a day to maintain 35%RH even during arctic weather.


To me that sounds more reasonable than 3 - 6 GPH.

Have you had any issues with yours ? What make / model ?


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## HybridFyre

sloeffle said:


> I was looking at one of the newer drainless units and they say it can put up to 16 or 18 gallons of water into the air everyday. It looks like it depends on the model that you have:
> 
> http://docs.electronicaircleaners.com/aprilaire_humidifier_selection.pdf
> 
> Based on the model, and furnace usage. You could theoretically use up to 144 gallons of water a day.
> 
> I balked at the idea of installing one after hearing too many stories of rusted HVAC ductwork and flooded basements.
> 
> Scott



This is what happened with our furnace with the previous house owners. The unit rusted out one whole side of the furnace jacket where the unit was installed. They ended up just disconnecting it and leaving it there. We're putting in a standalone unit to replace it.


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## woodgeek

sloeffle said:


> To me that sounds more reasonable than 3 - 6 GPH.
> 
> Have you had any issues with yours ? What make / model ?



I've got a cheapo 5 gpd evaporative (wick) jobber I found on amazon years ago. Stand alone. I previously became sensitized to the white dust from the ultrasound ones (my whole face was swelling up ). YMMV


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## woodgeek

1750 said:


> I just checked the temp of the water coming out of the drain pipe and it's really cold.   The vaporization really pulls the heat out of it!
> 
> It would be interesting to know how much water is actually being used across the course of the day.



The exiting water will cool to the dewpoint of the exiting air stream.  Unless you are overhumidifying, that can be very cold.


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## GaryGary

Hi,
It seems like 6 gallons of water a day would take about (6 gal)(8.3 lb/gal)(970 BTU/lb) = 48,000 BTU to evaporate, and that heat must be coming from the house and adds to the heating bill?  In other words, the furnace airstream is cooled by evaporating the water -- kind of like a swamp cooler.

I guess the idea is to get the humidity up to where it feels more comfortable in the house?

Our house normally runs at about 20% RH (no humidifier), and this does not seem to cause any problems -- or, maybe there are some health effects I don't know about?

Gary


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## woodgeek

GaryGary said:


> Hi,
> It seems like 6 gallons of water a day would take about (6 gal)(8.3 lb/gal)(970 BTU/lb) = 48,000 BTU to evaporate, and that heat must be coming from the house and adds to the heating bill?  In other words, the furnace airstream is cooled by evaporating the water -- kind of like a swamp cooler.
> 
> ....maybe there are some health effects I don't know about?



Yup.  I run 3 gal/day in January, so call it 1,000 BTU/h.  The unit makes the corner its in a little chilly.

We find we're a lot healthier if we keep things above 30% RH.  My house will maintain that on its own when it is close to freezing or above, so I only really drag out darn thing for 3-6 weeks a year.

Airsealing is huge for RH. Before I did that we would cruise at 15-19% RH for months, and during really cold spells the furniture would fall apart.


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## 1750

sloeffle said:


> I was looking at one of the newer drainless units and they say it can put up to 16 or 18 gallons of water into the air everyday. It looks like it depends on the model that you have:
> 
> http://docs.electronicaircleaners.com/aprilaire_humidifier_selection.pdf
> 
> Based on the model, and furnace usage. You could theoretically use up to 144 gallons of water a day.


Thanks for posting that chart.  Ours is the 600, so it's rated at ~ 3GPH when it's running.   That surprises me and is much more than it seems like is moving through the drain, so maybe most of it is getting into the air as intended?



woodgeek said:


> I've got a cheapo 5 gpd evaporative (wick) jobber I found on amazon years ago. Stand alone. I previously became sensitized to the white dust from the ultrasound ones (my whole face was swelling up ). YMMV



That sounds like a better idea if it gets distributed through the house well.  I wonder how evenly this moves from areas of higher to lower RH.

Our house is running about 30% RH, but when it gets really cold out (single digits F and below), the humidifier seems like it's running about all the time.  



GaryGary said:


> Hi,
> It seems like 6 gallons of water a day would take about (6 gal)(8.3 lb/gal)(970 BTU/lb) = 48,000 BTU to evaporate, and that heat must be coming from the house and adds to the heating bill?  In other words, the furnace airstream is cooled by evaporating the water -- kind of like a swamp cooler.
> 
> I guess the idea is to get the humidity up to where it feels more comfortable in the house?
> 
> Our house normally runs at about 20% RH (no humidifier), and this does not seem to cause any problems -- or, maybe there are some health effects I don't know about?


Maybe that's why it's on the hot water line, to reduce the amount of heat sucked out of the furnace to heat the water to evaporation?  I don't notice lower RH, but my wife complains about itchy skin.   I do notice also the wood floors seem to like more moisture in the air, as well.


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## woodgeek

1750 said:


> That sounds like a better idea if it gets distributed through the house well.  I wonder how evenly this moves from areas of higher to lower RH.



I've got forced air, and the cfm of the blower is a lot higher (like 10x) than the leakage cfm...seems pretty well mixed.


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## 1750

woodgeek said:


> I've got forced air, and the cfm of the blower is a lot higher (like 10x) than the leakage cfm...seems pretty well mixed.


Sorry, I don't understand what you mean by "leakage cfm."

I have a stand alone dehumidifier, and just sort of assume that as I create a little island of less humid air the inclination toward homeostasis keeps moving the moister air toward the dehumidifier, leading to a general reduction in the humidity level of the whole house.  Alternatively, maybe it's magic.  Double-alternatively, maybe this doesn't happen and I just have a little dry-air island in the room the machine is in.    

I'm assuming your stand alone humidifier works in the same way -- though better if the air gets moved around via your cold air returns?


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## woodgeek

Sorry.  I was estimating the rate of air exchange between the inside of my house and the outside.  In the winter (the period we are talking about) this is the measured blower door leakage rate at a pressure of 50 Pascals (created by the blower), CFM50, divided by a seat of the pants correction, of about 15-20.  The resulting number CFMnat, estimates the average amount of wind and stack driven leakage.  My CFM50 was around 1800, so I am getting ~100 cfm of fresh air through drafts.  Since my HVAC blower is 1400 cfm, and on much of the time, the air in my house gets to travel through my blower ducts about 14 times before it ends up back outside.  So it gets mixed up pretty well.

More to the point, the measured RH all over my house is the same.

I also put the humidifier on the lower level of my house, where the dry air comes in.  If I stuck it in a bedroom, it might leak out the window before getting mixed in.


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## 1750

Thanks for taking the time to explain that.   100 cfm via leakage seems like a "lot" to me... I'm thinking of a cube 5x5x4 sneaking into the house every minute... but I'm sure if that's what yours is, mine's much worse!   

This thread is making me think about shutting the water supply down on the furnace humidifier.   

Thanks again.


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