Exhaust Fan-DuctWork Help

[chatyak]

I need some assistance from those of you who are really good with working on renovation projects. I know ZERO when it comes to installing things because I've never had to deal with an issue however I would like to learn.

My fish room has so much humidity that a dehumidifier I have empties a good 3-4 gallons of water a day. The cost to run this 24/7 is not fun. I thought of installing an exhaust fan into the return line ductwork - which goes back to the furnance.

Can't put holes in the wall to the outside - home is a rental. However the home has ductwork such as the picture here:

So my question is... could I install a fan such as one here

and simply screw it in-between the beams of my ceiling? I'd cut a hole in the return ductwork and just place it in there... so humidity can be returned to the furnance/ac.

Is this a good idea?

Much appreciated!

 

[Misled]

Not really a good idea. It will add too much moisture to the furnace. Just exhaust it outside.

 

[TAB]

the very last thing you want to do is dump it into the HVAC system.

Is there a window?

 

[chatyak]

There isn't a window in the fish room.

These two pictures are of my actual fish room. The outside of the home is brick.

 

[chatyak]

Not really a good idea. It will add too much moisture to the furnace. Just exhaust it outside.

I wasn't aware that adding moisture into the system would be a bad thing. What is the reason for this?

Thank you

 

[chatyak]

I'm not sure what to do now... not sure if I can install an exhaust to the outside since it is a rental

On a better note... here is a FTS:

 

[Skins]

Where is your laundry room at? If it is near, tie in to the dryer exhaust. Put a backflow preventer on it.

I'm no HVAC guy but I know the returns are cold air returns feeding the furnace fresh air to heat again. I don't know if warm boyant air will counter act the flow but I do know
I wouldn't want salt laden air being piped directly into my heater.

 

[on the spot]

Is there a window anywhere in the basement? PVC duct to the window. Remove the glass, install a piece if plywood. Install a dryer vent, connect the pvc, etc...

A hole in the wall is better than mold. That seems like a lot of evaporation, how big is the tank? Are you using fans?

 

[Misled]

You don't dump moisture laden air into a heating unit. Your heating unit would rust out in a year. When the heat isn't running, the moisture would coat the ductwork and the heat chamber. When the heat kicks on, the moisture and most likely mold gets blown through the house.

 

[Fibinotchi]

It depends on the furnace, the new high efficiency furnaces remove moisture from the house via condensate drains and are designed that way. If running properly shouldn't have a problem with rust, however you would only be removing humidity when the furnace is running which probably wouldn't be enough for your fish room unless you live in a cold climate. I would put a bathroom exhaust fan in on a programmable timer and have it run 10 minutes or so an hour. You also should get some glass tops for your tanks and sump which you can have custom made.

 

[sasharotty]

It depends on the furnace, the new high efficiency furnaces remove moisture from the house via condensate drains and are designed that way. If running properly shouldn't have a problem with rust, however you would only be removing humidity when the furnace is running which probably wouldn't be enough for your fish room unless you live in a cold climate. I would put a bathroom exhaust fan in on a programmable timer and have it run 10 minutes or so an hour. You also should get some glass tops for your tanks and sump which you can have custom made.

Bad advice, the 90+ furnaces make their own water and drain via codensate drains.Has nothing to do with removing moisture from the airstream.It will have a problem with rust because it is saltwater.Even though most heat exchangers are stainless if you have a problem it WILL void a warranty.Somehow dump the humidity outside, DO NOT pipe it to the furnace.And you remove 0 humidity when a furnace is running.When the a/c is running you do.You can also look into a whole house dehumidifier but once again i wouldnt duct it to the furnace.

 

[wingedfish]

long time lurker, first time poster. I work in the hvac trade. couldn't help but join and comment. High efficiency furnaces do not take away humidity, nor are most furnaces stainless, nor will piping a return air into your fish room hurt your furnace. The water evaporating from your tanks are ending up in the envelope of the dwelling no matter what route it takes. the dehumidifier is an expensive way to bandaid a problem. If you exhaust air to the return air of the furnace, you will have no net gain. Exhausting to the outside will turn the house into a negative pressure and it will leak cold air where ever it can. Depending on how negative this is, it can suck cold air down the chimney and start you heating equipment back drafting. This can potentially be fatal.

The ideal and proper way to keep humidity in check, is an HRV. A step below this would be a small exhaust fan (cheap bathroom fan) to the outside. Don't pipe it into the furnace return air. The fish room humidity will be the same as the house and all will still be too high relative to the outside temp.


Keep in mind, the less humidity in the house, the more evaporation from the tank.

 

[sasharotty]

nor are most furnaces stainless, nor will piping a return air into your fish room hurt your furnace.

I disagree, most furnaces use stainless for their heat exchangers.And are you saying bringing saltwater laden air wont affect a furnace?? I disagree with that as well.And yes most of the salt stays on evaporation but you will still see some salt in the air that will have a negative effect on a furnace.If you add a bathroom 4" fan you will not create a negative pressure in the house.

 

[wingedfish]

Most furnaces are aluminized steel primary heat exchangers, And a high efficiency has a secondary that is stainless with abs plastic end caps. The makeup of the exchanger is not relevant.

Salt laden air? is your tank in your house? do you have a forced air hvac system? is it compromised do to having a tank in the house? Do you believe pulling a 4" pipe at 60% humidity and 25 cfm and diluting into the return of a furnace pulling 1200 cfm at house humidity is going to have any effect on the lifespan of the furnace?

I do agree that it's pointless.

 

[chatyak]

Exhausting to the outside will turn the house into a negative pressure and it will leak cold air where ever it can. Depending on how negative this is, it can suck cold air down the chimney and start you heating equipment back drafting. This can potentially be fatal.

Lots of interesting points all, thank you. I do not understand this statement however. Are you saying by putting an exhaust van to the outside, it is potentially fatal to people inside the home?

 

[chatyak]

Where is your laundry room at? If it is near, tie in to the dryer exhaust. Put a backflow preventer on it.

I'm no HVAC guy but I know the returns are cold air returns feeding the furnace fresh air to heat again. I don't know if warm boyant air will counter act the flow but I do know
I wouldn't want salt laden air being piped directly into my heater.

Too far away.

 

[TAB]

Lots of interesting points all, thank you. I do not understand this statement however. Are you saying by putting an exhaust van to the outside, it is potentially fatal to people inside the home?

it could be. now you have to under stand that its very rare, but it could happen.

Remember for air to go out, air has to be coming in. if the only place that can really happen is your exhast ports... it can make them work in reverse.

Not only would they pull out side air in, they would not let the exhuast gases out.

 

[Fibinotchi]

Bad advice, the 90+ furnaces make their own water and drain via codensate drains.Has nothing to do with removing moisture from the airstream.It will have a problem with rust because it is saltwater.Even though most heat exchangers are stainless if you have a problem it WILL void a warranty.Somehow dump the humidity outside, DO NOT pipe it to the furnace.And you remove 0 humidity when a furnace is running.When the a/c is running you do.You can also look into a whole house dehumidifier but once again i wouldnt duct it to the furnace.

So as your pulling moist return air across the heat exchanger, you wont be removing moisture at that point?

 

[hvacman250]

So as your pulling moist return air across the heat exchanger, you wont be removing moisture at that point?

Such crazy advice in this thread!

1. Heat exchangers are about 50/50 stainless vs. aluminized steel. Lower end units typically are aluminized steel, higher end units are stainless. The industry has gotton away from the clamshell type HE and most have gone to a tubular design. The industry is slowly converting to stainless because they last MUCH longer, but alot are alum. steel to keep cost down.

2. IME, the salt laden air you would pull into a return will do minimal damage to the heat exchanger(s). The main component that is affected is the cooling/evaporator coil. Salt water will eat it up in 5 years, give or take a few. On the flip side, the tank is inside the house, so theres not much you CAN do to eliminate this effect.

3. IME, the cheapest, most efficient thing you can do is use a dehumidifier in the fish room, and try to seal the fish room off from the house as much as possible. Weatherstripping, etc around doors that enter into the main living area.

4. 90+ furnaces DO NOT remove mosture from the air. They create moisture as a by-product of combustion (heat, water, CO2), and must drain it from the secondary heat exchanger. And sure, the heat echanger will evaporate some of the mosture that passes by when its on, but negligible.

5. An HRV is good advise, but too expensive, as is a whole house dehumidifier. You're talking $1000 plus for either for a quality system.

6. Buy a $300 room de-hum from a box store. Pay the $xx.xx amount it costs to operate, and buy a new one when they break every 3-5 years.:hmm3:

-or-

Vent the room air to outside via a fan. If you have to cut thru brick, see if you can find matching brick. When you move out, pay a mason to install 5-6 brick in place of the hole. That shouldnt cost but a couple hundred bucks. Unless you have the tightest house EVER built, a couple hundred CFM duct fan pulling air out will not affect any appliances.

 

[chatyak]

Such crazy advice in this thread!

1. Heat exchangers are about 50/50 stainless vs. aluminized steel. Lower end units typically are aluminized steel, higher end units are stainless. The industry has gotton away from the clamshell type HE and most have gone to a tubular design. The industry is slowly converting to stainless because they last MUCH longer, but alot are alum. steel to keep cost down.

2. IME, the salt laden air you would pull into a return will do minimal damage to the heat exchanger(s). The main component that is affected is the cooling/evaporator coil. Salt water will eat it up in 5 years, give or take a few. On the flip side, the tank is inside the house, so theres not much you CAN do to eliminate this effect.

3. IME, the cheapest, most efficient thing you can do is use a dehumidifier in the fish room, and try to seal the fish room off from the house as much as possible. Weatherstripping, etc around doors that enter into the main living area.

4. 90+ furnaces DO NOT remove mosture from the air. They create moisture as a by-product of combustion (heat, water, CO2), and must drain it from the secondary heat exchanger. And sure, the heat echanger will evaporate some of the mosture that passes by when its on, but negligible.

5. An HRV is good advise, but too expensive, as is a whole house dehumidifier. You're talking $1000 plus for either for a quality system.

6. Buy a $300 room de-hum from a box store. Pay the $xx.xx amount it costs to operate, and buy a new one when they break every 3-5 years.:hmm3:

-or-

Vent the room air to outside via a fan. If you have to cut thru brick, see if you can find matching brick. When you move out, pay a mason to install 5-6 brick in place of the hole. That shouldnt cost but a couple hundred bucks. Unless you have the tightest house EVER built, a couple hundred CFM duct fan pulling air out will not affect any appliances.

Thank you for this advice-good stuff. I always pictured my future tank in a dedicated fish room, with one big fan bringing air in from the outside, and another fan blowing air back to the outdoors. (Just for the fish room).

Two fans to keep things simple. This would also work yes?


Also - what sort of dangerous gases can build up in the house? I can think of CO2 buildup from exhaling our own breath. But other than that? This home is from the 1950s. Just a basic furnace in the basement, stove up in the kitchen. I'd like to know more about this just to learn what appliances can cause these gases.

Thanks!