Originally Posted by teddy bear
You should be pushing dehumidifiers where they are really needed like damp musty crawlspaces or houses with poor HVAC systems where it is more economical to add a dehu than to rip open walls and ceilings to replace the duct work.
If someone truly wants that steady non stop fresh air the erv is the way to go, and with a tight home a small inexpensive 40 pint dehumidifers are going to remove all the moisture in 'shoulder seasons'
Intermittent exhausts are not problematic until you get into the magnitude of Jenn Air grilles, stainless steel hoods. In that case the 50 CFM brought in by an over priced thermastor dehumidifer is going to be very insignificant.
With a tight home the original poster should be looking at the combustion appliances to be all sealed combustion and directly vented and it is wrong to even suggest a little bit of ventialtion air is even sufficient for combustion purposes.
Thanks for adding your info here as well. The more the better usually
Just a quick update for you and maybe you can add some info
New Construction home 2500 sq ft, 2 story. Spray foam insulation Low E-4 anderson windows Home should be very tight
They had the home sized for 2.5 ton upstairs and 2 ton downstairs Lennox XP16 heat pumps. (found out they don't make 1/2 ton sizes addressing this with a new manual J)
G61V furnaces backup natural gas (how are these vented are they sealed?
The only other gas appliance is a water heater and Im sure its a spec water heater and is naturally vented.
Kitchen as a microwave oven that vents outside all 3 baths have vents that vent outside as well and a electric dryer.
So my questions are that all my estimates and encluding contacting the reps about the foam they all said I need some type of way to introduce fresh air into the house such as an ERV.
They guys over at energywise structures said even the tighest homes have enough leaks that supplemental air infiltration is not neaded? any info would help
Here were my questions. Spray foam guy said you need some type of ERV for your home
Not 100% sure how running another Manual J addresses the no 2.5 ton 2 stage Lennox.
Originally Posted by acnoob1
Unless they fudged the loads to begin with.
For as tight, and well constructed as your house is suppose to be. 4.5 tons sounds like a lot of cooling.
Have you seen the actual numbers, or just told what it came out to.
The GV61 is a sealed combustion furnace.
I think they fudged the numbers quite a bit and that was part of the deal I could have a manual J done by a 3rd party to see what they came out with. I have a fealing that I could get by with 2 2ton units. Actually I probably could get by with smaller but they don't make anything smaller, Then again I will wait and see what the manual J comes up with.
Your house may only need 1.5 tons on the first floor and 2 tons on the second.
They make single staged 1.5 ton units.
If your floor plan is open to the second floor, even a 2 stage 2 ton, may not be able to remove enough moisture.
The first to second is not really open just the stair case that goes from 1st to second
Is this new Manual J coming from a third party.
yes a 3rd party uninvolved with this.
House do leak, and the use of small intermitent fans is not a problem with respect to the house sturcture and moisture moving through the building envelope.
Originally Posted by acnoob1
Drying a couple loads of laundry is not problematic with respect to how mositure moves through the wall.
Something that constantly exhausts air without any make up air can be very problematic in the cooling season, especially in a humid climate.
The ERV is its own exhaust and make up air system. So if you want a steady supply of fresh air with the lowest energy bills, this is the way to go.
Where intermittent exhaust can be a problem is with respect to combustion appliances, and the best way of taking this out of the equation is to use sealed combustion appliances that have combustion air directly connected to the outside as well as their own vents directly to the outside.The exhausts can make air flow down the chimney in some cases.
When you start taking about large exhaust appliances like Jenn Air down draft grilles and eleborate kitchen hoods with commercial grade cooking appliances under them, then you will start running into a lot of problems, and something of this scale will need an interlocked make up air system that runs whenever the exhaust runs.
Here is the attachment on my 2,300 sqft home. We were dry yesterday, 83^F with a 60^F outdoor dew point. Today we get your weather. The make up fresh air yesterday would have made my basement 70%RH without a dehumdifier. My dehu removed 30 lbs. of moisture. An ERV would have started out removing half of moistue in the make-up air. That only slows the wetting of your home. After an air change of fresh, the air exiting through the ERV has more moisture. The more moist air removes less moisture from the incoming damp air. After several air changes, the air exiting your home is as wet as the being bought in. Once your home is wet, the ERV exhaust wet air which will wet incoming dry air. Thus slowing the drying of your home with dry outside air. They only work if you can keep your home dry. During wet cool weather, a good dehumidifier works well.
Originally Posted by teddy bear
The other issue is the size of the a/c. With supplemental dehumidification, you are not dependent on the a/c to keep your home dry during wet cool weather. My graph shows the point. I have a 50%RH home with less than 2 hours of cooling. My 2 ton a/c is grossly oversized for a 2 hour cooling, but I have 50%RH with 58 cfm of fresh make-up air.
Check out the dew points in MO today. They are as high Miami.
We are getting your weather today. Hoping for wet weather to collect more data. Are you having fun yet? 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"
You run your air handler fan steady, a known way of elevating your Rh but still the main floor hovers around 50% RH, and the cooler basement was 55%
then you start pumping in outside air, the mainfloor rises a little and the basement starts rising up towards 60%.
The AC cycles on RH drops right down below 45% and as soon as it cycles off the main floor RH the constant fan re-evaporates 0.25 pounds off of that 2 ton coil and gives a slight increase in RH.
All in all it looks like everything is good even with the constant fan until you deliberately pump in the outside air.
The RH from that fresh air goes into the solid portions of the home, perhaps try and see how many air changes it will take to get the outdoor dewpoint down in your basement. I think that you will find it quickly rises up to half the initial difference between inside and outside, then it slowly climbs up. Moisture is being driven into your dry wall, furniture
An ERV would need maybe 3.5 pounds of water removed
Last edited by Carnak; 07-25-2008 at 04:48 PM.