I have a tightly sealed house with sips,  and heat exchanger, and keep my humidity at about 50%. I have slightly positive pressure on the main floor, and because of this the indoor air is freezing my door lock. Just wondering if anyone has encountered this problem and how they might have managed it. I haven't been able to lock my door since mid December, and I'd like to rectify this. thanks. 

First, increase the ventilation rate/duty cycle on your HRV to limit to lower the humidity to ~30%, which will lower the frost potential. 50% RH is an upper bound for health & comfort, not some ideal. The health professionals recommend keeping conditioned air between 30-50%RH (ASHRAE says 25-65%). Keeping it at 50% RH all winter you're increasing the risk of creating mold rot conditions along exfiltration paths, since it will condense on any surface that is below 48-50F (which would be the majority of the exfiltration path.) At 30%RH it won't condense until it sees a 37-39F surface. That gives both your locks and building materials a fighting chance to dry out.

Alcohol based lock de-icers sold into the automotive market can probably free up the lock, but powdered graphite lock lubricant should be liberally applied as soon as you get it freed up to keep it from recurring. Graphite is hydrophobic, and resists condensation/frost formation (it's used in both ski bases and ski waxes for these properties.)

BTW: What is your climate/location?

I live in Quebec Canada and this week we were at -13 F for a few days and I had a small icicle at the bottom of my door handle.  I had thought 50 was more the mid range, but I will try to get it lower. It can still be quite humid here despite the cold, so the air exchanger can often have little or no effect on reducing humidity. I keep the basement at 40 with a dehumidifier, I will drop that down too.

That is great to know about the temperatures that condensation forms, thanks. And I will try the graphite as well, that has more dignity to it  than putting a plastic bag over the handle, my other plan. Have you heard of this before though? I've run it by a few people, builders included, and no one has heard of it.

Posted By mcbain on 25 Jan 2011 10:38 PM
I live in Quebec Canada and this week we were at -13 F for a few days and I had a small icicle at the bottom of my door handle.  I had thought 50 was more the mid range, but I will try to get it lower. It can still be quite humid here despite the cold, so the air exchanger can often have little or no effect on reducing humidity. I keep the basement at 40 with a dehumidifier, I will drop that down too.

That is great to know about the temperatures that condensation forms, thanks. And I will try the graphite as well, that has more dignity to it  than putting a plastic bag over the handle, my other plan. Have you heard of this before though? I've run it by a few people, builders included, and no one has heard of it.

When it's -13F/-25C and a most-humid 90%RH (outside), when you raise the temperature of that air to 68F/20C it will have an RH of 2.5%.   (Not 25%, not 50%)

Ventilation rate WILL determine your interior RH in winter, if you turn off that humidifier in the basement.

Humidifiers should (almost) never be necessary to keep it at 30% RH in a very tight house. Humidifiers can be a health-hazard to both humans and the structure if kept above 30-35% when it's very cold out, because any unintended air leakage would then have moisture issues along the exit path, leading to rot & mold conditions, etc.

Wasn't that a DEhumidifier in the basement?

Posted By Rosalinda on 26 Jan 2011 04:06 PM
Wasn't that a DEhumidifier in the basement?

OOPS! (DOH!!!)

Yes, I suppose it WAS!   (I should have more coffee before responding some days...)

A basement dehumidifier would be OK to set to 55-60% to keep it dry enough to be mold-free during humid summer weather.

To keep it down to 30-35% during the winter, running a higher duty cycle on the HRV is likely to be more efficient than running a dehumidifier, and would result in higher overall indoor air quality.  That approach doesn't work during warm humid weather though, when outdoor dew-points are high, and bringing in more outdoor air INCREASES the RH of the interior air.

mcbain-

If you haven't been able to lock the door since mid-December, maybe you could tell us the address and where the valuables are kept :-)

I agree with Dana about adjusting the humidity. Another thing to consider is storm doors if you do not already have them. They might raise the temperature of the inside door enough to help reduce freezing, and cut down on air infiltration and conductive heat loss through the door at the same time.

Lee Dodge
www.ResidentialEnergyLaboratory.com
in a Net-Zero Energy House

Sorry Lee, had to see all my valuables to afford the house.

And a storm door is something I haven't considered, I'd rather not but I will keep it in mind. I have gotten the humidity down to the mid to lower forties, that and with this cold spell breaking things have loosened up. There is no way I will make it below 40 % though, mostly because my wife said she'd leave me if I did with cracked fingers and chapped lips as grounds. I'm hoping 40% will do the trick. Do you guys actually keep your homes that low?

Dana-

With the humidity levels I have been trying to cope with the last couple of years, I have relied on a dehumidifier, why is it you don't recommend it for the winter? with the chimney effect my basement air is going to find its way up here, if that was at 35 or 40, would that not give me a head start up here?

How varied our living conditions are. It is currently humid outside for here, with a dry cold front coming in tomorrow. It is currently 34 F and 46% relative humidity outside, so a partial pressure of water of 0.30 kPa. At 67 F inside, this same partial pressure corresponds to a relative humidity of 13%, and that is probably close to what the house is. I have a cheap electronic hygrometer that measures between 20% and 90% relative humidities, but below 20% it registers either 20% or when it's really dry, LL%. It spends most of the time at LL% or 20%, but if I turn on a small humidifier, it will read 20%, meaning 20% or some undetermined amount lower. The house is reasonably tight, 2.45 ACH at 50 Pa, so about 0.15 natural ACH. I run an HRV on recirculate 2/3's of the time, with fresh air drawn in at about 49 cfm. The main purpose of the HRV this time of year is to recirculate the passive solar heating that occurs in part of the house to the remainder of the house.

mcbain's wife is correct; the low humidities dry out your skin this time of year.

Lee Dodge
www.ResidentialEnergyLaboratory.com
in a net-zero energy house

30-35% RH at 20C is not chapped-lip territory, but 20% is.

30-35% RH @ 10C, different story...

Relative-humidity is just that- relative (to the temperature). The 40% RH air in a 15C basement at will be ~29% RH if warmed up to 20C, or ~23% if warmed up to 25C.

The reason for keeping it lower in winter is to limit the amount of condensation/frost damage inside of building structures. At 30-35% RH @ 20C it's still comfortable & healthy, but going much lower isn't advisable. It's currently 16% RH and 20C in my office, and it feels a bit cool & dry, and I'm wearing a sweater, whereas at 33%/20C at home (and lower ventilation rates) it's practically T-shirt comfort for me. It has to be consistently below -10C outdoors for several days before the 20C interior air drops below 30%RH at my house (which happens, but the January average temp here is about -7C, so most days have high temps above -10C).

Allowing the basement to exceed 60% RH any time the air temp in the basement is over 20C is to invite mold growth, but 60%/20C air is still a comfortable & healthy 44%RH when warmed up to 25C, so circulating air between the warmer first floor & cooler basement isn't much of an issue.

Lee- 2.45ACH/50 isn't super tight, but probably tight enough that you could probably keep it at or above 30% RH by reducing the ventilation rate. You're throwing away latent heat if you're running a higher ventilation rate, and making up for it with the humidifier, which is consuming heat-of-vaporization energy (either by cooling the room air, or from heating elements in the humidifier, depending on type.)