I had a journeyman HVAC specialist in the house yesterday. He said its "as tight as a drum" leak wise. In his opinion a blower door test isn't needed.
We inspected the existing Honeywell humidifiers. Both are set at 100% humidity and in good order. The house is extremely dry.
You have to remember that the outdoor humidity in Calgary can be as low as 10% when a Chinook is rolling through. These are extreme conditions.
We reviewed my plan to install AA600s for base duty and AA800s for the extreme conditions and he agreed it was a good way to handle the situation.
He calculated the minimum necessary ventilation rate for the house and came up with 280 CFM. Thus he agrees with my desire to install 2 150 CFM HRVs.
Only in Canada! Two humidifiers going 24/7. The home is too air tight. There something wrong with this picture. This will be another learning experience, may be a little expensive.
Originally Posted by BigBear23
If your humidifiers are working and the home is very air tight, the windows should be condensing moisture during cold evenings.
Get some help from someone who knows building science principles and not selling something.
If your humidifiers are adding 2-3 lbs of moisture per hour and your home is <30%RH at 68^F, you have +150 cfm of fresh dry air infiltration passing through your home. If drier, you have more fresh air infiltrating your home. 280 cfm of ventilation is more fresh air than your home needs.
The HRVs will make your home much driers than it is now!! With all of the proposed changes, you will need 10 lbs. of moisture to humidify the space. This is 10,000 btus of evaporation heat per hour!!
Keep us posted on how this all works.
The home is airtight. We found a "fanless" heat exchanger hidden in the ducting allowing 150CFM or more into the house. Thus the low humidity.
The fanless heat exchanger isn't high quality. I'm replacing it with the fanned HRVs.
Standard minimum air exchange in a home is 1/3 volume per hour. The house is 37 x 52 x 3 floors x 9 foot ceilings. 52,000 ft^3. 52,000 x 0.3333 / 60 = 288 CFM. If you have less than that much air moving through the house, its going to be stuffy. We live in a house like that right now. No thanks.
The other thing I'm learning is that humidifiers effectively put out way less moisture than they are rated for. If both of the humidifiers in that house were putting out 18 gallons a day, there wouldn't be a low humidity problem.
Nobody talks about this, but the moisture uptake with cold water into a cold plenum is poor. In a tight, well insulated house running heat exchangers, the furnace doesn't run much. Even if the humidifiers are wired to demand the blower, the air in the plenum is 70F and not much gets absorbed. For maximum evaporation, the water going to the humidifiers should be hot, 140F. That will also cut down a bit on the chilling effect of adding the moisture.
Another issue is contamination of the evaporation pads with minerals. Calgary has hard water. I'm installing a water softener for this and other reasons.
Steam is the ultimate answer here, but its expensive to run when the boilers are electric. That is why I'll use evaps for the base load and steam for supplementation.
I'll probably also add a small duct fan to the bypass piping on the 600s to ensure lots of air flow through them. We are going to install them first and see how they run without.
There is no way a seasoned or as you put it a journeyman hvac specialist can tell how tight your house is without a blower door test done to CFM50 standards..
I have seen foamed insulated houses that are supposed to be airtight to the point of needing ventilation added that were as leaky or more so as a conventional home.
TB is correct if you have humidity issues with two operating humidifiers then you have serious air leakage or your leaving a window or door open..
This leakage could be caused by ducts leaking outside the envelope, supply ducts in attics are a major problem if leaky as the air that is leaked outside must be replaced by that dry outdoor air that is outside..
Get a blower door test performed to CFM50 standards and find your problem.. Your bills may be reduced, your comfort will be increased and your humidity level issues will go away...
Look for a company that is BPI certified or comfort institute certified..
We ran a blower door test and did some infra red camera snooping yesterday.
The house has a leakage rate of 0.215 volumes at 50 Pascals. It has an equivalent open area of 172 square inches. Given the size of the house, this is considered very good.
Infra red testing showed everything to be really good with the exception of pot lights in the upper floor, a leak in the attic entrance area and a leak where the gas line enters the house. Tightening up these areas will further reduce the air leakage rate.
The tester strongly agreed that a house this big and this tight needs an active ventilation system.