Adding dehumid - how to duct

18 years ago

I recently discovered that we have a mositure problem in the basement of my new home (been in it about 6 months). When the temps stayed low (around low 70's) and hunmdity climed to high 70% - we started seeing strange spots on the cement floors of the basement - also had a funny smell. I did my research and measured the humidity down there - very high. So I ordered a whole house demudifier made by Sante Fe. It is the HC model, with a 335 CFM capacity. I have a large basement - about 3900 sq feet. Now I need to figure out how to duct it. Can you help me?

I would really like to use the existing ducts in the basement. It is unfinished but I paid the builder to rough in the main ducts work down there so when i do finish it - all I need to do is add registers and controls. The diagram below is the way the HVAC is configured right now. Is there a way to use the existing duct work that feeds the basement rooms with one dehumidifer BUT 2 HVAC units? Could I just pump the dehumididied air into the returns for both HVAC A & B units and then just fugure a way to fire up the fans for both these units when the dehumidifer turns on to distribute the conditioned air?

Or, should I just run a separate duct for the dehumidifier like this?

Running a new set of duct work for the dehumidifier is not exactly easy since there are a lot of things in the way - but it is doable. If I do have to run a new set of ducts, the main supply duct will likely have a bend in it to get from one end of the basement to the other.

Thanks for the help

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Comments (6)

zl700
18 years ago
Looks like you have the same unit I do. Except that I am in Houston and it is just not the humidity but the heat too!

Being that I have no basement, mine is suspended in the 2nd floor attic with my two HVAC indoor units.

Have you heard of jumper grilles? I either till I moved here. We have central returns here except the Master Bedroom which has its own also. Some genius sold the homebuilder on installing these 12x12 grilles in each room that has a closeable door and using flex duct out to the general area with another 12x12 grill in ceiling. These are insulated boxes and connected with 10" R-8 or so flex.
The idea is if the door is closed, the room goes positive pressure and air is drawn through the return jumper grilles. While the do work have you ever heard of such a Mickey Mouse way?

So, I took these off and reducted and installed collars to my return plenums of my furnace and now have ducted filtered returns. On two of the grilles, I ducted to downstairs unit from the open space above allowing better mixing and exchange.

That left me with two grilles in the common area to deal with. What to do, drywall them over? Nope, those are now my supply and return for the remote central humidifier (has its own fan) and I installed a remote dehumidistat.

By reducing the indoor humidity by up to 20%, I have raised my stat 2+ degrees with no difference in perceived comfort.

Sniffdog, I would worry about ducting into existing systems the key is to keep the intake and exhaust separated. The humidity in the house will self balance.
zl700
18 years ago
That last line should read "I wouldn't worry"
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sniffdog
Original Author
18 years ago
z

so in my 2nd drawing, if I left the intake where it is, but put the exhaust on the opposite wall and dumped into the large room in the top left of the drawing that would be good enough? If that is the case, then my install will be very simple.

thanks
zl700
18 years ago
Sniff,
You got it, the moisture in the rest of the house will transfer naturally

I should add that those units should have some duct on them with turns as without they can be noisy.

Try to find some vibration isolators and suspend the unit,along with using a rubber flexable duct connector to the unit, you will be much happier
sniffdog
Original Author
18 years ago
z

i got my Sante Fe unit delivered on Friday and hooked it up right away - amazing! I purchased 10" insulated flex duct from Lowe's and used 2 25 foot sections - one for input and one for output. The unit isn't that loud.

I was able to drop the humidity level in the house (basement and main floor) from 65% to about 49% in 1 day. The house is very comfortable and no smell. Just in time for the nasty heat wave we are getting here on the east coast.

Thanks for the help.
zl700
18 years ago
COOL

I hear it is just as hot as it is in TX