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Discussion Starter · #1 ·
Hi, this is my first time posting here but I have been a homeowner for about 20yrs and done several DIY jobs over that time.

I have a few questions about basement dehumidification. Below is a layout of my basement, pretty close to scale. The home sits on the side of a hill, so the area is a walk out basement. It has a little bit of a musty smell. I have been tracking the humidity in the area, and in the summer it is high 50s to low 60s. The area is tied into the home's HVAC system, but there are not a lot of vents so it isn't fully controlled as the floors above. Year round it is the coldest place in the house. Per the diagram below, it is mostly finished, and mostly carpeted.

Rather than using floor standing humidifiers, I have been looking into a joist mount option that I could put into one of the unfinished closets, like a Santa Fe Compact70 and then I would run some 8" insulated(?) ductwork from there...but I have some questions.

1) Is this something that could be considered a DIY job? Getting electric to the unit won't be a problem, and if I put it into Closet#2 per below as a central location, I can easily plumb into the PVC pipes from the condensate drain of one of the HVAC units to deal with any condensed water.
2) Other recommendations on a dehumidifier unit if the Santa Fe mentioned above is not a good one
3) Best location in the basement for the dehumidifier
4) Where to run the HVAC vents with indications of return/supply
5) Any other considerations?

654803
 

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retired framer
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When the same air is in the basement and upstairs the moisture is the same but as it cools in the basement the humidity goes up.
So it does not mean you have a mysterious moisture supply down there.
Your unfinished closets are likely the source of the musty smell.
Insulated foundations below ground will be in the mid 50s degrees year round, moist air getting into contact with that, water will condense. That air also is not clean so dirt will be deposited with the water, mold will grow on that dirt .
 

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Discussion Starter · #3 ·
Thank you, that is something I hand't considered. So it sounds like it would be pointless to install a dehumidifier.
 

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retired framer
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Thank you, that is something I hand't considered. So it sounds like it would be pointless to install a dehumidifier.
I didn't say that, I just thought it would be good for you to have some idea of the cause.
 

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1) thogh shalt not alter the airflow in a gas furnace vent or gas water heater vent (except slighly positively, which though shall not leave untested first)

2) though shalt not install an air duct connected to a heater which touches anything flammable except indirectly by hanging straps, since it will cause a fire if the fire box fan for some reason cuts off the box gets really really hot

also the usual head/ac air flow rules apply

if it is an apartment: then you do NOT connect the upstairs and downstairs air supplies together (ie, do you want bathroom smells from one apartment being vented to another? no that's illegal)

that's all i know

Consider a window unit and an extra circulating fan it could save you a ton of time and money. You don't need "all that BTU" that you'd think because it's dry heat you may be comfy with less BTU than you think.

On the other hand: if your dis-satisifed with a window unit: consider a wholey separate 1 ton outdoor split system (maybe, get it on zoro). There is not much way to alter an existing system to serve a basement. There's allot of thinking planning testing and it's just not worth it because in the end it will likely end up wrong (not passing codes for rental / living spaces)

A window AC unit will de-humidify for you, of course. Also if your basement is "usually cool" then you doubly don't need many BTU to keep it cool and dry.

-------------------------------------------------
GOOD NEWS:

* if you want to circulate air purely for must, one trick is to install a "through vent" above doorways or in walls, except the bathroom (which by code is already separately vented). this doesn't require ducting is why i mentioned it. this works great of you have one return already and want it to pull the rest of the basement)

* you can use fans to move air to prevent must, it doesn't necessarily need to be centrally circulated. however if you want to use one "high test" fan, then you'll need a (return or supply) duct the length of most of the basement, yes
 

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Discussion Starter · #7 ·
Thank you for the response. Just for the record, I am not looking to, nor would I ever, modify the existing hvac ducts.

I will look into a window unit to see where that leads me.
 

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1) thogh shalt not alter the airflow in a gas furnace vent or gas water heater vent (except slighly positively, which though shall not leave untested first)

2) though shalt not install an air duct connected to a heater which touches anything flammable except indirectly by hanging straps, since it will cause a fire if the fire box fan for some reason cuts off the box gets really really hot

also the usual head/ac air flow rules apply

if it is an apartment: then you do NOT connect the upstairs and downstairs air supplies together (ie, do you want bathroom smells from one apartment being vented to another? no that's illegal)

that's all i know

Consider a window unit and an extra circulating fan it could save you a ton of time and money. You don't need "all that BTU" that you'd think because it's dry heat you may be comfy with less BTU than you think.

On the other hand: if your dis-satisifed with a window unit: consider a wholey separate 1 ton outdoor split system (maybe, get it on zoro). There is not much way to alter an existing system to serve a basement. There's allot of thinking planning testing and it's just not worth it because in the end it will likely end up wrong (not passing codes for rental / living spaces)

A window AC unit will de-humidify for you, of course. Also if your basement is "usually cool" then you doubly don't need many BTU to keep it cool and dry.

-------------------------------------------------
GOOD NEWS:

* if you want to circulate air purely for must, one trick is to install a "through vent" above doorways or in walls, except the bathroom (which by code is already separately vented). this doesn't require ducting is why i mentioned it. this works great of you have one return already and want it to pull the rest of the basement)

* you can use fans to move air to prevent must, it doesn't necessarily need to be centrally circulated. however if you want to use one "high test" fan, then you'll need a (return or supply) duct the length of most of the basement, yes
Huh?

1) irrelevant for this situation
2) mostly irrelevant these days for any modern-ish unit.
3) he wants to dehumify, not cool the place. I've never seen a window Dehumidifier. Floor portable units are readily available.
4) must basements will never pass as a legit apartment without serious work. A nanny apartment can share air. Most basements already do share air if the furnace is located there.

Cheers!
 

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Hi, this is my first time posting here but I have been a homeowner for about 20yrs and done several DIY jobs over that time.

I have a few questions about basement dehumidification. Below is a layout of my basement, pretty close to scale. The home sits on the side of a hill, so the area is a walk out basement. It has a little bit of a musty smell. I have been tracking the humidity in the area, and in the summer it is high 50s to low 60s. The area is tied into the home's HVAC system, but there are not a lot of vents so it isn't fully controlled as the floors above. Year round it is the coldest place in the house. Per the diagram below, it is mostly finished, and mostly carpeted.

Rather than using floor standing humidifiers, I have been looking into a joist mount option that I could put into one of the unfinished closets, like a Santa Fe Compact70 and then I would run some 8" insulated(?) ductwork from there...but I have some questions.

1) Is this something that could be considered a DIY job? Getting electric to the unit won't be a problem, and if I put it into Closet#2 per below as a central location, I can easily plumb into the PVC pipes from the condensate drain of one of the HVAC units to deal with any condensed water.
2) Other recommendations on a dehumidifier unit if the Santa Fe mentioned above is not a good one
3) Best location in the basement for the dehumidifier
4) Where to run the HVAC vents with indications of return/supply
5) Any other considerations?

View attachment 654803
47 Pints / 22.2 Litres / 5.875 Gallons per Day @ 70°F (21°C) and 60%RH

Do you currently use dehumifiers? If so, what size? How many?

The compact 70 should be ok, but be aware that they are rated at 80°f / 60% rh. The cooler the basement, the less effective any humidifier is.

Humidity will even out naturally, even without airflow. So you don't necessarily need the flex ducting. It does speed things up though, so if it's not too difficult to run the flex lines, it'll still beneficial. It'll also help reduce the air noise from it.

Cheers!
 

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Discussion Starter · #10 ·
47 Pints / 22.2 Litres / 5.875 Gallons per Day @ 70°F (21°C) and 60%RH

Do you currently use dehumifiers? If so, what size? How many?

The compact 70 should be ok, but be aware that they are rated at 80°f / 60% rh. The cooler the basement, the less effective any humidifier is.

Cheers!
Thanks for the response. No, we don't have any dehumidifiers in the home.
 

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I would try a standalone one (looking at 30 pint +) & see how it works for you first before going - hey I want a whole... In general, I would say most houses do better having a dehumidifier in the basement & I shoot for 40 to 45 humidity level. If you do go standalone, leave the doors open unless in use. The biggest issue with standalones is where to drain it with hose or remembering to check it often enough.
 

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Thanks for the response. No, we don't have any dehumidifiers in the home.
Without knowing how much humidity you need to remove, it's a bit of a stab in the dark. If you don't want the floor models, the compact 70 is a good place to start.

Cheers!
 

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The Santa Fe 70 is probably about as small as you should go.

Don't get a window A/C instead, as that will just make the humidity worse if you cool the area more than it is..
 
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