Fresh Air Return Duct Insulation is Dripping Wet

Crissie

Is anyone familiar with these fresh air return duct dampered systems? I had one installed 3 yrs ago. This is a 6" duct that was put through rim joist to bring fresh air into the return system when furnace operates. It is a Honeywell system that uses a damper, set to open for different sq ft sizes of home only when furnace runs. Brings in 90 CFM of air.
The duct runs through my basement to main return duct of furnace. It solid duct with a 1-2" insulated wrapped around it. In the Winter, this insulation is soaking wet. I assume it caused by ice cold air entering a warmer basement. It concerns me because I don't know what is taking place inside the duct, is it the same level of condensation?
I began getting ill from my HVAC not long after this was installed. I need it though, need mechanical ventilation in my home. I'm also not thrilled it terminated just 6" above my back patio, but it never get's snow in this spot.
Any insight would be helpful.

Jamie Hall

See my comment on the heat recovery ventilators. It is no surprise that that duct and insulation is dripping wet. I'd bet that the interior of that duct is pretty scuzzy... get rid of it.

In general, looking at you various posts, I get the very strong impression that you have a slightly -- but only slightly -- more than usually miserable forced air heating system. Stop worrying about it and put in hot water...

pecmsg

There should be NO water and or moisture inside the return in the winter. Winter RH levels are lower. THe sweating on the outside says the crawlspace it too humid.

Crissie

@pecmsg It is in a basement with humidity less than 35%.

Jamie Hall

If your basement is at 60 with a relative humidity of 35%, the dewpoint is 32 F... and that pipe will be drenched. In fact, it may be that pipe which is controlling the relative humidity in the basement, and it's a pretty poor way to do it.

But @pecmsg is fright -- the inside of the pipe should at least be dryish...

pecmsg

Jamie Hall said:

If your basement is at 60 with a relative humidity of 35%, the dewpoint is 32 F... and that pipe will be drenched. In fact, it may be that pipe which is controlling the relative humidity in the basement, and it's a pretty poor way to do it. But @pecmsg is fright -- the inside of the pipe should at least be dryish...

Exactly my point. We need more information. 

Crissie

Basement has a dehumidifier going nearly year round. I turn it off in dead of winter when living area is very dry (22-28%) humidity. Basement is somewhere between 30-35% in winter.

pecmsg

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

neilc

pecmsg said:

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

give some serious thought to A Team Adam, or the other vendor, recommended by Rich49, and their HVAC 2.0 program,
it does sound like there's more going on there than the internet may figure out.

not to worry you further, but,
do you have a digital CO detector there, one that you can push the "peak" button and see lower levels than would cause an alarm ?

Jamie Hall

Crissie said:

Basement has a dehumidifier going nearly year round. I turn it off in dead of winter when living area is very dry (22-28%) humidity. Basement is somewhere between 30-35% in winter.

pecmsg said:

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

Let us suppose for the sake of discussion. Basement temperature 60 F. Basement relative humidity 32%. With that specific combination, the basement air dewpoint is 30.1 F. If the incoming air through that duct is less than that temperature, moisture will condense on the duct. Sorry about that. Physics is a b___h. Nothing else needs to be going on.

Crissie

@neilc I have several companies come in a test C02 along with everything else. I rented my own monitor. It is not that. I only feel ill when the HVAC is running and it is worst when it is stressed. Not sure if you saw my other posts, but the return ducts were tampered with, large 3+ inch hole left in return and super leaky supply. It was taking ceiling cavity rockwool insulation and construction dust through it every time it ran.

Regarding the sweating return duct. Oddly enough I had an HVAC guy out about 2 yrs ago to give me a quote on a minisplit for one room, he was walking through my system and pointed out to me the insulation was wet and that it is 'always wet' for the dampered return fresh air intake. He said that was norm for his customers who have this. I hate it, makes me think there is all sort of weird condensation going on with the ice cold air coming in. Going to replace it with an ERV. Furnace is way over-sized, starved for return air, literally pulling air from the foundation and walls every time it runs. Thank you though for your comments and am on it. Just wanted some feedback from this group on the soaking wet.

Rich_49

neilc said:

pecmsg said:

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

give some serious thought to A Team Adam, or the other vendor, recommended by Rich49, and their HVAC 2.0 program,
it does sound like there's more going on there than the internet may figure out.

not to worry you further, but,
do you have a digital CO detector there, one that you can push the "peak" button and see lower levels than would cause an alarm ?

Neilc , where are you from ?

Crissie

Let us suppose for the sake of discussion. Basement temperature 60 F. Basement relative humidity 32%. With that specific combination, the basement air dewpoint is 30.1 F. If the incoming air through that duct is less than that temperature, moisture will condense on the duct. Sorry about that. Physics is a b___h. Nothing else needs to be going on.

@Jamie Hall Then what will stop this same thing from occurring with an ERV. Either way, warmer air from the home is going to mix with colder air from outside. Even with an inline dehumidifier, how dry can you get the air, at some point there will always be 60 - 70 degree air touching 5 degree air somewhere in the system. Then will the filter / inside of ERV become soaking wet?

Jamie Hall

As I mentioned before, @Crissie , with a sensible heat only ERV, you will get condensation at some point in the outlet side. That should not be a problem -- the unit should be equipped to drain that condensate. Further, the ducting should be such that cold outside air goes immediately -- or if not immediately by the shortest possible route -- to the ERV. There will be no condensation on the inside of the inlet -- the air is much too dry for that. Also, if there is a filter on the inlet, it will see no condensation either -- again, the air is much too dry. There is no need for a filter on the outlet, so that's not a problem.

It's important, though perhaps not obvious, that the two air flows never mix or come in contact with each other, either directly or indirectly. They are always separated by a metal barrier. Thin, yes, but no mixing or contact.

If is necessary to have any significant length of duct between the outside air intake, I recommend that it be a duct within a duct. The inner duct carries the outside air. The outer duct (it could reasonably be hooked to the exhaust of the unit) carries air too, so there may be condensation on the wall of the inner pipe, but like the exchanger itself it could be provided with a drain.

A good -- probably better and certainly easier --alternative is to have the intake duct covered in closed cell spray foam. At least two and better four inches of the stuff. This will ensure that while the temperature within the insulation will drop below the space dewpoint somewhere, being closed cell there can be no moist air at that depth, and thus no condensation.

ChrisJ

pecmsg said:

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

My dad's plastic fresh air intake for combustion on his direct vent furnace not only sweats but frosts in his basement when it's -20F out and the RH in the basement is no higher than 35% @ 55F.

Dew points aren't mysterious....

There's no evil afoot.

pecmsg

ChrisJ said:

My dad's plastic fresh air intake for combustion on his direct vent furnace not only sweats but frosts in his basement when it's -20F out and the RH in the basement is no higher than 35% @ 55F.

Dew points aren't mysterious....

There's no evil afoot.

pecmsg said:

Then theres something else going on. Winter RH levels are low! Why is the duct sweating?

But the OP has insulation on the duct. Possibly compromised we dont know.

Jamie Hall

The OP's insulation appears to be fiberglass. Which is not closed cell, and thus moisture can -- and will -- get into it and freeze or at least drip. Fiberglass -- or any insulation which is not closed cell -- must never be used in a situation where it is possible to reach the dewpoint in the insulation thickness, unless it has a really impermeable vapour barrier on the warm side. The paper backing of matts is not adequate.

ChrisJ

@Crissie
Please post pictures of the outdoor termination as well as of the duct that sweats, from start to finish showing the insulation, and the ends of the duct and any joints or gaps in the insulation.

I would expect this to have a plastic/metal insulation on it with all joints taped.

Solid_Fuel_Man

Keep in mind that an ERV has a membrane heat exchanger which the humidity wont be completly removed in winter. 

And HRV has a plastic or metal heat exchanger which will remove indoor humidity in the winter. 

Basically a tight house should use a HRV and ERV is better suited to a leaky house or one where air conditioning is used in the summer. 

Fiberglass sucks for pretty much everything....they make cigarette filters out of the stuff.... the duct would have to be insulated with a closed cell foam etc to not sweat. 

Jamie Hall

Not only does an ERV recover some of the moisture... it recovers most of the pathogens and any water soluble contaminants as well. Just wonderful... I would never recommend using one. Only an HRV.

mattmia2

I'm wondering if you could use that almost sheet mastic like insulation that they use on refrigeration lines, it isn't very thick but it is enough to keep its surface above the dewpoint and it molds and seals to the surface then put another type of insulation on top of that.(although now that I type it I am thinking the other insulation may reduce the surface temp of the mastic like insulation and cause condensation on its surface.)

ChrisJ

I've seen so many people bad mouth fiberglass on here and yet I still choose it over spray foam for most things.   Spray foam is like a nightmare in many ways.

Fiberglass does fine with an appropriate vapor barrier.

EBEBRATT-Ed

As @Jamie Hallsaid the duct will sweat below 30 deg all you have to do is look at the pysco chart

it should be insulated or lined with armaflex 

Jamie Hall

If fiberglass does not and cannot be exposed to air below the dewpoint of that air, it's excellent insulation. If it is, however, the moisture will condense and the insulation will get soaked and will lose its insulation value. Use the right stuff in the right place...

neilc

Rich_49 said:

Neilc , where are you from ?

Ct

neilc

Crissie said:

@neilc I have several companies come in a test C02

Crissie, note that I said CO, carbon monoxide, not CO2, dioxide,
i'm thinking exhaust leak, with it's moisture,

Crissie

ChrisJ said:

@Crissie
Please post pictures of the outdoor termination as well as of the duct that sweats, from start to finish showing the insulation, and the ends of the duct and any joints or gaps in the insulation.

I would expect this to have a plastic/metal insulation on it with all joints taped.

Crissie

neilc said:

Crissie said:

@neilc I have several companies come in a test C02

Crissie, note that I said CO, carbon monoxide, not CO2, dioxide,
i'm thinking exhaust leak, with it's moisture,

I had my house tested for all of those by several contractor and the company who did the Blower door. I don't have any of those gases in my house. Asking about the Fresh Air Return because I plan to replace it with an ERV but now I think an HRV with inline dehumidifier would be better.

Crissie

Solid_Fuel_Man said:

Keep in mind that an ERV has a membrane heat exchanger which the humidity wont be completly removed in winter. 

And HRV has a plastic or metal heat exchanger which will remove indoor humidity in the winter. 

Basically a tight house should use a HRV and ERV is better suited to a leaky house or one where air conditioning is used in the summer. 

Fiberglass sucks for pretty much everything....they make cigarette filters out of the stuff.... the duct would have to be insulated with a closed cell foam etc to not sweat. 

I have a tight house, but Chicago we get several months / year of very humid weather.

Jamie Hall

Crissie said:

neilc said:

Crissie said:

@neilc I have several companies come in a test C02

Crissie, note that I said CO, carbon monoxide, not CO2, dioxide,
i'm thinking exhaust leak, with it's moisture,

I had my house tested for all of those by several contractor and the company who did the Blower door. I don't have any of those gases in my house. Asking about the Fresh Air Return because I plan to replace it with an ERV but now I think an HRV with inline dehumidifier would be better.

An HRV would be much better! But why an inline dehumidifier? You might need it in the summer, but if you're mostly concerned about winter conditions, the air the HRV brings in will be considerably drier.

Crissie

An HRV would be much better! But why an inline dehumidifier? You might need it in the summer, but if you're mostly concerned about winter conditions, the air the HRV brings in will be considerably drier.

I need mechanical ventilation all year. It is very humid here, even in April and Oct. It can be 60 degrees outside with 60-75% humidity.

Jamie Hall

So long as the outside air is cooler than the inside, the HRV will act as a sort of dehumidifier (it isn't, actually -- the actual dew point doesn't change -- but the relative humidity decreases as the air warms going through it). Now. You might find that you need it during the hot weather, when (assuming your air conditioning is running) the HRV is actually cooling the incoming air. Then I can see you might want it, but only when the HRV is acting to cool the incoming air.

I have to chuckle just a little, though... where we are, 75% relative humidity in the summer is low...

Solid_Fuel_Man

Also consider a heat pump water heater. I use one in the summer for dehumidification. At least not all the energy is wasted running a compressor. 

Also, consider that a dehumidifier will add some heat to the air. 

As Jamie said, here in the northeast we have RH of 85%+ all summer. I turn off all ventilation in the summer. 

ChrisJ

That looks like an exhaust for air, not an inlet.

Why would that ever sweat?

KC_Jones

ChrisJ said:

That looks like an exhaust for air, not an inlet.

Why would that ever sweat?

Looks like a dryer vent outlet that requires airflow out to open, so if it had airflow going in it should actually pull it shut tight.

neilc

can we see past the damper and sheetmetal connection, to the left more,
to what does that connect?

Crissie

neilc said:

can we see past the damper and sheetmetal connection, to the left more,
to what does that connect?

It is connecting to the return duct for the furnace. The picture is of a 6 inch solid duct pipe with insulation wrapped around it, that runs out the rim joist, terminates about 8 inches above my patio. It is a damper controlled fresh air return. When the furnace runs, it pulls in a huge amount of air. Unconditioned air. This type of ventilation is often required by code here in my county for new construction because homes are built so tight. I believe the sweating is because the air is unconditioned. That is what many have told me.

ChrisJ

Crissie said:

can we see past the damper and sheetmetal connection, to the left more, to what does that connect?

It is connecting to the return duct for the furnace. The picture is of a 6 inch solid duct pipe with insulation wrapped around it, that runs out the rim joist, terminates about 8 inches above my patio. It is a damper controlled fresh air return. When the furnace runs, it pulls in a huge amount of air. Unconditioned air. This type of ventilation is often required by code here in my county for new construction because homes are built so tight. I believe the sweating is because the air is unconditioned. That is what many have told me.

The outdoor damper you showed us is an exhaust.  

neilc

unless it is propped / held open somehow, as shown in that picture,
plots thicken , , ,

Crissie

The outdoor damper you showed us is an exhaust.  

The cover of it might look like an exhaust, but it is an intake. It pulls air in when the HVAC is running. Here is a link to the product. https://www.honeywellhome.com/us/en/products/air/ventilation/fresh-air-ventilation-system-with-truezone-damper-y8150a1017-u/

Rich_49

Crissie said:

The outdoor damper you showed us is an exhaust.  

The cover of it might look like an exhaust, but it is an intake. It pulls air in when the HVAC is running. Here is a link to the product. https://www.honeywellhome.com/us/en/products/air/ventilation/fresh-air-ventilation-system-with-truezone-damper-y8150a1017-u/

Crissie , I think you misunderstand what is being said . Nobody is questioning the parts that make up the Honetwell kit . The termination that has been used is in fact an exhaust termination most usually used for a gas dryer . It may have been used as an outdoor termination by someone but that does not make it so , those louvers open outward , not inward , ever . You would have been better suited with a hooded , open ended termination with stainless steel screen as a bug shield . No doubt in my mind that the damper system works , there is however a doubt whether the intended airflow can be pulled through the SLITS in that louver .