Supply and Return Placement for dehumidifier with ductless a/c
I’m familiar with the reasons why a dehumidifier is a bad idea. I know it’s basically a space heater and that I’m putting a bad bandaid on the fact that my mini split system is oversized.
But I built this house several years ago and in my naïveté, I was opposed to resistance electric heat, so I sized them system adequately for the heat load based on a manual J.
But now I’m debating on how to apply the bandaid. My initial thought was to install the return at the top of the stairwell and run dual supplies on either side of the lower level. The upper level continually measures higher humidity (per the norm) and the lower level is primarily where the system is oversized, so it will more easily accommodate the additional heat load.
Anyone care to agree or disagree with the placement?
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Replies
Seems to me where you collect the air from does not matter very much in that the humidity level in the house will be more or less the same everywhere but high if fine if you can get the duct work in place.
Where you discharge could be a comfort issue as this air will be 20° or so warmer than the room air and if you dump it all in one place it could get quite warm in that spot. You may want to spread it around.
Walta
I'm considering a whole-house dehumidifier for my leaky single-level home and noodling over where to locate the return and supply ducts. I'm leaning toward placing intakes in the main bath and the laundry and a single exhaust supply in the main living space near one of the HVAC systems returns. (I also might add a supply to the main bedroom.) I'm open to reconsidering this layout if one of the experts advises otherwise, however.
user-2310254
“I'm considering a whole-house dehumidifier for my leaky single-level home “
This is crazy have you considered actually fixing the leaks?
Walt
Hi Walta,
Point taken. I'm slowly tightening up the house. Since it's a typical production build, there's a lot to address air-tightness-wise. In any case, I suspect I'll need mechanical dehumidification. One of my previous homes was pretty tight (around 2ACH/50) needed a ventilator/dehumidifier for much of the year to keep humidity levels in the safe range. Not a lot of humid outdoor air was making it's way inside, but the HVAC system still couldn't keep up with the moisture being produced by occupants, laundry, and cooking.
I don't know the reasoning behind this, but this is what I found in an installation manual:
"When installing the DH90 in a structure that does
not have a forced air HVAC system, a single return
for the DH90 should be installed in central open
area of the structure.
DO NOT locate the return in a bathroom or a
kitchen. The supplies of the DH90 should be
located in the remote areas of the structure (such
as bedrooms, den, etc.). By ducting this way, the
air inside the structure will circulate through the
DH90 to be filtered and dehumidified."
I wouldn’t say that you did anything wrong by sizing the system(s) for the heat load or by opposing electric resistance heat. Maybe your system(s) don’t modulate down low enough to adequately remove moisture before they turn off? What kind of system(s) do you have and how low do they modulate? Have you tried turning some of them off so what remains on is not oversized for the load? Does the fan run even after the compressor turns off? Do you have a dry mode option? Do you have multiple heads connected to one outdoor unit? Have you had anyone look at it to diagnose the problem? I’m not saying that you don’t need a dehumidifier. I’m just wondering if all avenues were explored and perhaps the cost of the dehumidifier could be used towards the cost of correcting some problems.