So even in New york kind of weather a normal house will not need the humidifier in the cold of the winter?
That's right. If the house and ducts are reasonably well sealed and the duct design is reasonably well balanced, there would be no need for a humidifier unless an unusually high ventilation rate needed to be maintained. Sure, if this is a house full of smokers who burn incense, use plug-in "air fresheners" to keep the stink at bay you may need continuous mechanical ventilation at rates high enough that it would need humidifiers to keep it from dropping below 30% RH @ 70F indoors, even NYC.
If the ducts are unbalanced creating large room-to-room pressure differences "the Great Outdoors" becomes part of the return path to relieve those pressure differences. Even in fairly tight houses high rates of air handler driven infiltration can occur if the ducts are unbalanced. Doored-off rooms that have only supply ducts, no returns are often big offenders, yet relatively easy to fix by creating adequate return paths (with transom grilles, jump ducts etc.)
As a case in point- I live in a somewhat colder climate than NYC/Westchester/Long Island, in a location more comparable to Syracuse or Rochester. After tightening up the both the house and ducts (both circa 1923) the wintertime indoor humidity stays above 30% RH except after several days of extreme Polar Vortex cold snap sub zero F weather, and this is even
with continuous active HRV ventilation covering parts of the house, and liberal use of exhaust venting in the bath/kitchen areas.
My HVAC guy did half A$$ job on sealing so I bought mastic and got to sealing all I could,
The Aprilaire 700 is a bad design after having it installed on my supply side, there is now ay to stop the air leak from that device, we need it for 2 to 3 months to increase the humidity in the house the rest of the year it is just air leak in the supply side... the only way to seal that thing is to use whole lot of of duct tape at the end of season and take them off for winter...
I hope it is not installed in series with the supply plenum, with 100% of the supply air running through it(?). It's way too small and restrictive to be used that way in most systems, creating huge static pressure drops even with fairly small air handlers. Putting it in parallel with the filter & furnace with a take-off from a near-furnace supply duct (or the supply plenum), and installing it on the return plenum before the filter still moves enough air through it to provide the humidification function without causing high static pressures, which also increases leakage. If the return paths are constrictive (closed door, no dedicated return) the static pressures and leakage on the supply ducts increase, and more (potentially unhealthy) air gets sucked in to the return ducting, and the greater the room to room pressure differences become.
An Energy Star duct system needs to have <3 pascals pressure difference between rooms under all air handler speeds, all conditions- doors open, doors closed. That's not too hard to hit if the returns are sized adequately, but impossible without a properly sized dedicated return path for every supply register in rooms that can be isolated by closing the door.
Another big factor in air handler driven air infiltration stems from oversizing of the furnace or AC. Higher BTU/hr rates require higher cfm out of the air handler & ducts, inducing higher pressures. In NYC most central AC systems would have air handers in the 350-400 cfm/ton range to have reasonable latent cooling capacity, though it could easily be north of 500 cfm/ton. Typical hot air furnaces in the northeast are 3x or more oversized for the actual heating loads. Lower cfm yields lower duct velocity dramatically lowers the static pressure or "friction loss" in the ducts. A velocity of 600 feet per minute (pretty commonly designed in for hot air furnaces) creates 4x the amount of friction loss at 300 cfm. Where possible I personally recommend keeping duct velocities under 400 fpm, which keeps down the noise levels, and allows filter to work better at any MERV rating. Increasing the size of the return plenum to lower duct velocity to <300 fpm and installing large 4"-6" pleated filter media allows high MERV filters to be used without exceeding static pressure limits on the air handler. At <300fpm a MERV 13 filter performs almost like a HEPA filter.
So, to mitigate against the need to run the humidifier to stay comfortable in winter take these steps:
#1: Start by identifying and rectifying any return path issues on the duct system.
#2: Do a
serious round of air sealing on the house itself. If you're not a DIYer willing to get dirty in awkward places start by hiring an air sealing contractor that uses blower doors and infra-red imaging to find & fix the big leaks. Some of the big leaks are obvious and can be found & fixed without chasing it with equipment, but many big leaks are more subtle. A DIYer can do almost as well as the pros using a $200 FLIR One IR camera and a 16" reversible window fan, but it takes more time. The biggest less-obvious untreated (but easy to fix) air leak in most houses with basements or crawlspaces is the joint between the foundation & foundation sill, and the band joist. In most cases this leak exceeds all window & door crackage in the house combined, often by a few hundred percent (!).
3: Figure out the oversizing factors of your equipment. Since it's the cooling season, measure the duty cycle of your AC condenser on afternoons that cross your
1% outside design temp. (About 88-90F in your area.) Take a look at
this bit o' bloggery for ideas on how to go about it. If on afternoons when it's in the high 80s/low 90s outside it's running less than 50 minutes out of every hour ( a 60min/50 min= 1.2x oversize factor) the AC is suboptimally oversized for comfort. If it's running less than 40 minutes per hour (=1.5x oversized) it is high enough to be an efficiency problem.
If you have some of last winter's heating bills, run the fuel-use against heating degree-day data from a nearby weather station to estimate the oversize factor of the furnace as outlined in
this other bit o' bloggery. Be sure to use winter-time fuel bills only (to reduce the errors from solar gain and other uses of the same fuel.) If you can share the fill up or meter reading dates & amounts (gallons or therms, not dollars) and the nameplate BTU-in/DOE-out of the furnace I can run those numbers for you here on the forum.
If it turns out you can replace a system with a 1500-2000cfm air handler (~80-100KBTU furnace, 3.5-5 tons of AC) with an 800-1200 cfm air handler (35-50,000 BTU/hr heating, 2-3 tons AC) you'll end up with longer, more comfortable run times, but also with dramatically less air handler driven infiltration, and higher wintertime indoor humidity. While it's not necessarily going to be economic to replace the oversized equipment on an energy cost basis, it's sometimes necessary to make the house truly comfortable. See the short videos linked to on these pages:
Home Comfort 101
HVAC 101
HVAC 102
