Regular Guest
I have benefitted enormously from reading these forums, so I'm a bit of a "long time listener, first-time caller" here!
The Background:
I'm looking quite seriously into whole-house dehumidifiers, with the primary goal being decreased humidity in the winter months. We are in a 1600sqft cinder block home (built in '52) in the Shenandoah Valley in Virginia. Smooth stucco exterior (no air gap, no nothing) and interior plaster directly over the block (no air gap, no wall board, no nothing). Having replaced all windows and been zealous about air sealing while doing so (in other words, tightening the envelope), we have had trouble the past few winters with direct condensation in bedrooms, leading to mold growth and funk. We are now looking at spray foaming the roof deck, so things will be even tighter.
I'm hoping that we can knock out most of this trouble with a whole house dehumidifier tied in to our forced-air HVAC system, and possibly with ceiling fans in the bedrooms for even more air mixing/movement. I have paid most attention to Aprilaire and to Ultra-Aire products, in both cases assuming we will also have the optional ventilation duct installed to add fresh air to the house. Our ~1000sqft, basically unfinished basement does not have water infiltration problems, but is definitely musty and humid. Finally facing reality down there (rather than staying in denial), I bought a hygrometer at Lowes and am finding 70% readings to be common over the past two weeks.
The Question:
I was very excited to see that Aprilaire units can actually be "zoned" now - with a primary/secondary setup and controlled dampers. This would let me kill two birds with one stone, drying out the basement, removing odors and nastiness down there, while also dehumidifying the house as needed. As far as I can tell, Ultra-Aire does not have this same zoning option. This seems a bit surprising to me, so I figured I would put it to folks here for follow up: can Ultra-Aire dehumidifiers be zoned in this way? Or is Aprilaire my only option for a two-zone central dehumidifier?
Long run-up to a basic question, I know....but I also would welcome any other comments/suggestions about this setup that folks might offer!
Professional Member*
It's early in the morning, and I'm having a little trouble getting my mind around your question. I understand your thinking, however, to my simple mind, is Honeywell zoning the return side? That to me would make the most sense.
I've been out of the business for 3 yrs. and never got into the whole house dehumidifiers much (expense), but I knew the need would increase, because of all of the oversizing (keeping the same size, primarily) of the new high efficiency equipment.
Regular Guest
Sorry - could have explained a bit further. Basically Aprilaire units (a couple of them at least) can be ducted to two distinct zones on both supply and return. They have a kit for this with 4 dampers and a control unit, so that, in my case, I could have a supply/return zone that covers my basement and a supply/return zone tied into my existing HVAC supply/return. The system can be programmed, with one zone as primary and the other secondary, so that the dehumidifier focuses attention on the primary zone but can override that when the secondary calls for dehumidification. From what I can tell, people used to do some hacks to accomplish this by pulling return air (to the dehumidifier) from the basement and running supply (from the dehumidifier) into the HVAC supply, or other such combinations. The appeal of the ducted system with Aprilaire is that it minimizes mixing of house and basement air and allows for more precise control. I'm curious if Ultra-aire (and rebadged systems...like Honeywell?) allow for this kind of zoning as well.Originally Posted by George2
Sponsor & Professional Member*
Typically, the moisture content (dew point) in the air of home is fairly equal. But the temps vary like in a basement, the temp is 65-68^F and the main floor is 75^F, yet if the dew point is 50^F, the %RH in the basement 58%RH, while the mainfloor is 50%RH. This is because the difference in temperature. In most cases, you maintain the critical area at the desired %RH. If the basement is finished with carpeting on the concrete floor, set the dehumidistat to maintain 50%-55%RH in the basement. Because of moisture desire to equalize the mainfloor will be 45%-50%RH at 75^F.
If you have special needs to control to maintain specific humidity levels in different areas, supply/return ducts with dampers and dehumidistat can be arrange to control different areas at different %RHs. Moisture is much more aggresive than hot/cold air to equalize throughout the structure.
With all of that, I suggest you start with two dampered supplies to specific areas of concern. Seasonally, adjust to meet you need. Locate the dehumidistat in the most critical area. If you find that the needs vary on a day to day basis, add a second dehumiditstat and electric dampers. Either dehumidistat will activate the dehumidifier and open/close the dampers.
Regarding winter humidity control on cold walls, This is a sign of in adequate fresh air change in a normal home. Homes need a fresh air change in 4-5 hours when occupied. Outside cold winter air is very low dew point and will usually make the home dry enough to avoid condensation mason block or windows. Because the dry air is free with exception of needing a small amount of heat, it is more economical to use than a dehumidifier.
Consider that the Ultra-Aire are the most energy efficient dehus make and will deliver dew points that near or below freezing for these precise moisture control situations.
Recognizing the need for fresh air as part of this solution, I suggest using the DEH3000 controller which will bring fresh on a occupancy basis and maintain %RH independently. Secondary dehumidistats can be added as needed to activate the dehumidifier independently.
For specific help with special design considerations, contact the factory, 800 533 7533 or continue posting questions.
Regards TB
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
Regular Guest
Teddy Bear -- This is very helpful - thanks! I'm having a little trouble picturing exactly what you mean here:
Are you saying I duct two supply lines from the dehumidifier directly to specific rooms in the house (which is to say: dedicated ducts just for this purpose)? Or, do you mean one to the house via the central supply and one to the basement? In both cases, from where would I be pulling air to the dehumidifier (what I would consider the "return" to the dehumidifier)?
And, how would this be helping me dehumidify the basement directly? Or, maybe what you also mean in your first paragraph about RH and temp differences is that the actual moisture content of the air will be stabilized in both basement and house just by managing one space directly with the dehumidifier?
Sponsor & Professional Member*
Typically, you duct you split the dehu supply to the a/c supply and the basement with a damper in the basement duct. This allows you to balance the basement with the rest of the home. The return to the dehumidifier is from the open part of the open living area. Plus the most have a partial return from outside to provide fresh air when occupied or needed. The outside fresh air may have an electric damper controlled to provide fresh on demand.
The puts a small amount of positive pressure on the basement to discourage soil gas infiltration. A partial return could be ducted from the basement also.
You are dealing with 200-300 of supply/return air. This is small compared to the a/c or heating.
Regards TB
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
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