Low wintertime RH in a residential structure in most US climate zones would be an indication that your ventilation (aka infiltration) rates are too high. Unless your average outdoor temps are below 5F fo days/weeks or the cubic-feet of interior volume per human is very high or something, maintaining 30% RH would not need humidifiers in a tight (but not necessarily super-tight) home, and still have adequate ventilation rates for healthy air quality. (You DO have to be consistent about running kitchen & bath exhaust appropriately though.

Fix the air leaks and you''ll fix the dry air problem. In 10000 heating-degree day climates it might be tough to make it fully tight enough as a retrofit though.

Humidifiers in leaky houses can increase problems that may have previously been minimal too. With more moisture in the air, there is more condensation potential on the exfiltration paths, leading to higher risk of mold/rot issues. Unless you're religious about cleaning them, humidifiers that use wicking elements (but not the HM509) can become a breeding ground for molds, and a dispenser of mold spores thorughout the house via your HVAC. Tightening the house and minimizing humidifier use is almost always a better/safer option. In super-tight houses wintertime RH can be (and often is) controlled by the duty-cycle of the heat-recovery ventilation system under DEhumidistat control alone.

Where are you located?

Hello Thanks for the reply.

Im in Caledon, Ontario.

Last couple days its been 2f to 9F and below that. Its up and down.

If I didn't have a humidfiier my RH would go down to 18%.

I had a energy audit test done, blower test and it came back at 86 score.

Our home is fairly tight.

If your daily highs are staying below -13C for days, it takes an unusually (but not impossibly) tight house to keep it above 30% during those periods, but you probably aren't rotting the structure out from under you with the humidifer. Still that water is going somewhere...

I'm not sure what an 86 score on a blower door test means in terms of air changes per hour & 50 pascals or some other standard metric. Can you give us a hint? (I tried to google it, looked at R-2000 standard stuff and came up blank.) The US EnergyStar minimums for air tightness aren't really very tight at all compared to R-2000, and while considered "fairly tight", probably not tight enough to reliably keep humidity above 30% with weekly average outdoor temps much below -15C. I'd be surprised if you needed to add humidity very often in Caledon if you met the R-2000 standard of 1.5ACH/50 though.

Your typical January averages are ~-6C, nearly identical to mine (Worcester, MA), and while we too get cold snaps, I rarely see indoor humidity below 25%RH @ 20C even without active humidification. It's not the tightest house on the block by any means, but I've been air-sealing and insulating a bit- maybe it's time to get the ACH/50 numbers checked on my place. (I've been curious.)