RH too high, fresh air too low, how can I stop my windows from sweating?
I built my house without considering that I could possibly build a “too-tight” envelope. I guess I just figured that some fresh air would find it’s way inside. I have Pella Architect Series Aluminum Clad wood windows and three to four times a day I have to wipe down the glass, meeting rails, bottom rails and sills. I would say that these windows are collecting ounces of water in the form of condensation. This happens in every room in the house. I have sufficient cfm exhaust fans in the kitchen and bathroom, but I have no fresh air intake. The HVAC system is a Carrier Infinity system, but I have not yet bought the Infinity Thermostat…I have a single stage Honeywell programmable thermostat. No Infinity controller, means I do not have control over the relative humidity of the indoor conditioned air. I am seriously considering getting the controller…but, I am unconvinced that this is the answer to my problem. I have recently kept a small awning window on the first floor cracked open a couple of inches, and periodically crack open windows on the second floor. I also run the vent fans for thirty minutes at a time several times a day. This helps marginally with the humidity issues, but not entirely. My thermostat is set to 71 degrees. Oh, and I have R-13 and/or R-19 in my 2×4 or 2×6 perimeter walls, R-30 in an un-vented 2×12 warm roof, with 1.5″ polyiso above. I used gap-n-crack and window/door foam by the case. Is there enough information here for someone to give me some solutions? Please help. I am worried that I am going to have rotting windows by the end of winter.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Roy,
Oops. You forgot to install a mechanical ventilation system.
Every house needs one, so you'll have to do some retrofit work. If you don't know what type of ventilation system to install, I recommend that your read the following article: Designing a Good Ventilation System.
FIND THE SOURCE FIRST
And of course, Martin is right on with the ventilation requirements.
If you have control over occupant generated moisture, you might want to consider the possibility that the moisture is emanating from your basement or crawl-space, if you have one. If that is the case, sealing these surfaces would go a long way toward decreasing the RH in your home. It has to come from somewhere. Always deal with moisture at the source. you may have ground water issues i.e. gutters, downspouts, grading, etc... as the source.
When we perform energy retrofits, we often air-seal and insulate. If there are basement or crawl-space moisture issues, they have to be dealt with first. We also address bath and kitchen exhaust at the same time.
I was in a 80 year old home this morning and there was condensation on ever window in the house. It was gutted and remodeled less than a year ago. When I went into the basement (dirt floor with active bulk water infiltration) it was obvious that it was the source of the moisture. The basement was very "connected" to the rest of the home with no thermal or air pressure boundary. We need to stop the bulk water infiltration, seal the floor and walls, establish the thermal and air pressure boundaries and hopefully will have taken one giant step towards solving the condensation problems.
Hope I have helped!
Other things to double check are to make sure the HVAC and water heater drain their condensate properly and the HVAC systems whole house humidifier, if any, is NOT adding moisture unintentionally.
Roy,
Martin's right. Since this is a new house, it's not likely that you have a major uncontrolled water source, such as a wet basement or crawlspace. A typical family of four puts 4-5 gallons of water per day into the interior environment just from the normal activities of living. That water needs to be vented out.
Some of that occurs when you run your kitchen and bath fans when those rooms are generating moisture, and you noticed a marginal improvement when you ran those fans more often. What you need is to put programmable timers on each bathroom exhaust fan and set them for 0.25 complete house air changes per 24 hours.
If you don't want to pay for the heating cost of air exchange in the winter, then you need to consider a heat recovery ventilator.
It's not just the windows which will eventually rot, but everything inside your walls and roof.
More of a question than a comment...But could there be something wrong with the windows?
I mean the amount of condensation described either means the humidity is way way higher than a normal range (considering there are operating bath and kitchen fans) or the temperature on the surface of the windows is much cooler than it should be.
As Robert eludes to, it seems like there are more serious moisture issues than just poor ventilation.
Roy,
I pity the poor window reps. When this problem happens, many people blame the windows, and the rep has to come out and make a site visit. It's almost never the fault of the windows, however, especially in a new home.
I assume these new Pella windows are double-glazed. They may even be low-e, although that's just a guess. If they are new, they're probably fine.
This sounds like a house with normal construction moisture and no mechanical ventilation system.
More info on the construction details would be useful. When was the house built, when was it completed, is it slab on grade or does it have a concrete basement, any interior poly sheeting on the walls, what type of siding and WRB, what is the square footage and how high are the ceilings, and yeah... where are you and what's the climate?
Also, this caught my attention:
Actually, I said it WAS almost certainly because of inadequate ventilation.
Either that, or there's a humidifier running that shouldn't be.
Sorry Robert, I was referring to your first post -"Find the source first"
Thanks to everyone for their insights and answers. I am aware that I need a mechanical ventilation system, but I am unsure whether I can simply run a 4" duct from a fresh air vent in the basement, directly into the return duct on the HVAC...or if I have to install an entirely new and substantial HRV/ERV system throughout the entire house?
I should fill you in on the construction of my house for better understanding of the problem. This is a 100+ yo, 1000 sf, double wythe brick party wall, double wythe brick facade row-house, adjacent buildings occupied. I kept the party walls, and facade, and removed everything else. All new floor and roof joists, 2x4 interior framing, with a 300 sf, 2 story addition to the rear of the building. (1000sf total, not including unfinished, concrete slab basement.) The 8'x16' addition is comprised of xps insulated cmu foundation walls, 2x6 wood framing, Dow SIS sheathing, Certainteed cement board panels over a .5" cavity rain-screen, R-19 batt, over a concrete slab crawl-space, with direct access into the full-height original basement. The existing foundation walls of the row-home are rubble, parged and damp-proofed. The basement is unheated and more than likely has significant infiltration of moisture from the ground and outside, despite a proper underslab moisture barrier. I am now convinced that I need a de-humidifier for the basement and some type of mechanical ventilation...but to what extent must I go?
Turn off the water to the dehumidifier in your Carrier HVAC system. If it is on and out of control then this is your problem. If your home is tight you should never turn it on.
If you have lots of plants you should give them up till you have moisture under control.
Run bath fans long after bath use.
Stop boiling water if that is a nightly occurance.
You have way too much moisture right now. My best guess is one of the above is out of control. I never saw new construction cause as much moisture as you describe but there will be quite a bit during drywall taping and painting and right after.
Roy,
Thanks for the clarification. When you began with "I built my house" that made it appear to be new construction rather than the renovation that it is. That makes a huge difference.
A dehumidifier is the solution, but if there's a humidifier in the system that could be the problem. So could the possibly damp basement, but don't put a dehumidifier there until you've determined that's the source. Check it with a hygrometer. And make sure you air seal the basement to prevent its air from being drawn up into the house.
Whatever ventilation system you choose, it should meet the current ASHRAE 62.2 requirements of 15 cfm per person.
Roy,
You wrote, "I am unsure whether I can simply run a 4" duct from a fresh air vent in the basement, directly into the return duct on the HVAC...or if I have to install an entirely new and substantial HRV/ERV system throughout the entire house."
I urge you to read Designing a Good Ventilation System. Many of your questions are answered there.
Your proposal -- "run a 4-in. duct from a fresh air vent in the basement, directly into the return duct on the HVAC" -- describes one of three steps required to install a central-fan-integrated supply ventilation system. (It's possible, however, that your home needs a 6-in. instead of a 4-in. duct.) The other two steps which you forgot to describe are:
-- The passive air duct needs a motorized damper, and
-- The motorized damper and the air handler fan need to be controlled by an AirCycler control.
More information on these systems can be found on the AirCycler Web site.
Martin, please edit my post above to say humidifier. My ridiculous autospellchanger roofed my post up yet again. Thank you!
AJ,
If you provide your e-mail address when you log in, you should be able to edit your own posts.
Silicon is taking over ! ... now I wrote goofed and instead posted roofed! geesh...(now I caught the rascal wanting geese, ha ha)
Yes yes... Martin... some of my devices sign me in verified some don't... I let the tech win some battles... lol
You wrote:
"The basement is unheated and more than likely has significant infiltration of moisture from the ground and outside, despite a proper underslab moisture barrier. I am now convinced that I need a de-humidifier for the basement and some type of mechanical ventilation...but to what extent must I go?"
I wrote the post " find the source" above. It is well worth the time and effort to clearly identify the source or sources of your high RH. Eliminating or reducing excess water vapor at the source will make any mechanical aids such as a dehumidifier, ERV, or HRC easier to implement.
As Robert Riversong indicated, get a hygrometer and measure the basement humidity. Tape a square foot piece of clear plastic to the basement floor and walls to see if and where condensation forms. If it forms under the plastic, moisture is coming from the slab. Using a moisture meter measure the moisture content of the floor and walls.
If you don't own these tools, a good energy auditor, home inspector, or water infiltration specialist could help you with the diagnosis.
If you find that the basement masonry is a source of considerable moisture, you may consider sealing those masonry surfaces. You may also want to thoroughly assess roof water management if that is contributing to the moisture levels in the basement masonry.
Maybe placing several hygro-thermometer's at different points throughout your home would also help guide you to the source. They are inexpensive, under $15. In my own home I have three. Before I distributed them I place them side-by-side and calibrated.
In a perfect world, you would find the source, introduce solutions to mitigate or eliminate the moisture, and never need a dehumidifier.
Best of luck
Thanks again to all who answered my frustrated call for information. Martin, I appreciate the link to Designing a Good Ventilation System. I will be researching my best options in the coming days. But there is only one solution...I need the V in HVAC. Thanks again.
If you decide to spring for a dehumidifier, I suggest an Energy Star self-defrosting unit. I've seen several that turn into useless icecubes in the low 60F range.