Fall = High Humidity in the House

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Old 11-09-15, 12:11 PM
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Fall = High Humidity in the House

Hello all, Back again after last year battling humidity.

I live outside of the burbs of Minneapolis. My house is a two story ranch with a walk out basement, built in 1989, original windows. Built with above average quality of construction for the time period. The house is pretty tight, so in the fall, we have interior high humidity issue, until things dry out with the colder weather. I have measure the humidity across the house and its usually lowest in the basement where the air makeup dumps into the utility room.

If left unchecked we get to a humidity level of 60%, which results in window condensation as night time temps dip.

Last year I installed a new, big, 130 CFM fan in the master bath, with a variable 60 min timer. I recently installed a timer that an run up to 4 hours on a timer with an override on/off switch. I can control the humidity by more or less running the fan most of the day.

My house probably should have a HRV, but I don't really have that kind of coin at the moment.

So what I want to do is install a dual speed fan in the kids jack and jill bathroom that will run at a lower speed all the time, then based on humidity crank up. I have looked at a lot of fans to do that, but I haven't found one can can be turned off. Panasonic seems to have many options, but the ones set up to run like I would like, seem to be run at the lower speed all the time, without the ability to turn it off. I don't need to be pulling in hot humid air into the house during the summer.

I am also considering installing a 4 to 6 in freash air inlet from outside to the air handler return, and install a powered louver that would be controlled by a humidistat. I am a little worried this would create a positive pressure in the house.

Down the road when my life settles down a bit I will install a HRV. I have three kids under two... Its a little busy at my house.

In the mean time, any recommendations on duel speed bath fans with humidity sensors?
 
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Old 11-09-15, 01:48 PM
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Why not a dehumidifier? Or even a ventilating one if you want the outside air.
 
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Old 11-09-15, 08:31 PM
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Excellent question. Stand alone dehumidifiers are noisy and energy intensive, will still require air circulation to manage the whole circulating mass of the house, and there is still the need to turnover the air in the house. Ventilating dehumidifiers are expensive and energy intensive costing more than than a HRV installed.

I think the long term solution is a HRV, the short term is just ventilation.
 
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Old 11-10-15, 04:35 AM
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I reviewed your previous discussion and it looks like all suggestions have been considered. What I see missing is a determination as to where your problem originates. A blower door test can tell you how tight the house is and THEN you will know how much ventilation is necessary.

Understand, "too tight" is not easy to achieve and rare for the age of your house. The transition from tight to leaky occurs at around 1 complete air change every 3 hours. The reference target is 0.35 ACH (air changes per hour). Where it seems inefficient to simply crack a window open and leave it that way, or let a bath fan run 24/7 on low speed, the trade off is not energy, it is you deciding where that outside air enters. At 0.35 ACH, the incoming air filters through the walls and other leaks it can find. Seal much of that up and you have to provide new incoming air with a dedicated path. It is not a choice of simply living with half the normal ventilation.

You can fine tune the process by limiting the moisture sources allowing you to slightly reduce the fresh air, but anything less than 0,25 ACH can be a real problem, condensation being just one of them.

Bud
 
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Old 11-10-15, 05:22 AM
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An HRV has no humidity control. So incorporating a dehumidifier into the system would be best. Good dehumidifiers do a much better job at removing moisture so the energy consumption is far less than an off the shelf unit. If you think a dehumidifier is expensive to operate you should see what it cost your HVAC system to dehumidify that same air.
 
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Old 11-10-15, 07:27 AM
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Here in Washington 60% in the house is common during the rainy season. Never have condensation on windows which are double pane.
 
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Old 11-10-15, 07:37 AM
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The saturation limit of water in air increases exponentially with temperature. If the outside temperature is say 40F and about 85% relative humidity, heat that same air up to 70F would result in a 30% relative humidity. This leaves the air with the ability to absorb about 5 g water/kg air, to reach the maximum desirable interior relative humidity of 50%. From a cost stand point all we are talking about it the cost associated with the sensible heat required to heat the air fresh air 30F or so to the interior temp set point of 69F. My 3 ton, two stage, seer 16 AC would remove a lot of moisture for a long time before it would reach the capex of a ventilated dehumidifier. A Single room point dehumidifier isn't practical or desired in my application. The point of moisture introduction in the house isn't a wet basement. Its from a family of 5 living in a relatively tight house for its age. The only time high humidity is a problem is the fall. Another month and I will be considering the install of a whole house humidifier.

What I really need a continuous ventilation, and I am looking for the best most cost effective way to get that done, which would be a fan. As stated before a whole house dehumidifier has been ruled out as impractical and too expensive for my application.
 
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Old 11-10-15, 07:41 AM
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I lived in Pacific Northwest for a decade. The temp gradients from the inside to out were never that significant, and most of the condensation resulted on the incredibly poor choice to use aluminum as a window frame material. 40 degrees is cold in Seattle.
 
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Old 11-10-15, 08:10 AM
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So it really sounds like you answered your own question before you even posted. Buy the HRV. Or kind of sounds like you want an ERV if you are going to run bath fans all the time.
 
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Old 11-10-15, 08:17 AM
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Old 11-10-15, 08:40 AM
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Old 11-10-15, 08:48 AM
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Ultra-Aire 70H cost $1200 not installed, consumes 587 watts (as much as refrigerator).

XB110 ENERGY STARŪ Most Efficient 2015 -Ventilation Fans - Broan
This fan cost $160 not installed, consumes 23 watts. The cost of heating the 110 CFM air from outside would be a ~ $10/month assuming 80% operation in MN fall.

I am not currently in the position to buy a HRV, and a ERV would be pointless in my climate.
 
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Old 11-10-15, 09:03 AM
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Yea 1200 is pricey. Look around im less than that with a controller and motorized damper. But just crack a window 1/8 inch tell you can get the HRV.
 
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Old 11-10-15, 09:10 AM
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Is your walkout basement finished or exposed concrete walls?

Bud
 
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Old 11-10-15, 09:19 AM
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my basement is about 80% finished. The areas that are not, are isolated from from the HVAC system.
 
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Old 11-10-15, 10:58 AM
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Kelvin,
I'm going to bow out as I have prepared 3 long replies recently, but deleted them without posting because they disagree with what you firmly believe and I don't want to be that controversial.

Best,
Bud
 
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Old 11-19-15, 08:37 AM
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I thought I provide an update.

I installed a Panasonic variable speed fan with a motion sensor. I installed a switch on the fan so it only runs continuously when we need it during the fall.

The fan is set to run at 60 CFM continuously and bumps up to 80 CFM for spot ventilation based on the motion sensor.

The relative humidity in the house has gone from 60% down to 45%, and the window condensation issue has dissipated.

The fan with options cost about $170. I already had the insulated flexible duct on hand for the run through the roof pass through. Took me about 4 hours to install, much of that was spent moving around my attic, which has blown in insulation and isn't any fun to be in.

I am contemplating adding a second makeup air line to the house so each floor has its own dedicated makeup air inlet. I would likely add a humidity controlled damper to the upper level air makeup, if I did so.
 
 

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