Two condensation problems in a seasonal house:
1. Returned to our island house (coastal Maine) and went upstairs to admire my new drywall and paint job. Everythings looks good except for major mildew problem in one of the rooms. Not a leak, clearly mildewed condensation droplets. This is a ceiling below an unheated attic. R38 in attic floor, but there is a a hatch to the attic that I haven’t closed yet. (Working on the hatch door today.) All the other ceilings are fine. My theory is that cold air spilling out of the attic though the hatch chilled the ceiling, encouraging condensation on the newly painted ceiling. I washed it down with bleach and will re-paint, but am anxious to avoid future problems. The hatch will be closed, and we may leave some heat on in the winter if we need to leave the house again.
2. Our plumbing (pressure tank and electric hot water heater are in a 8X8 ft concrete block “cellar”. Last winter I tried to close gaps to keet squirrels and cold air out and warm air in. Expandable foam, foam board, etc. Seemed tight. And it is! But now there is major condensation on joists, some mildew. The “floor” (granite ledge) and walls are generally moist, but in the past moisture escaped through gaps below sill plate, etc. Clearly a ventilation problem, but how do I ventilate a cellar I’m trying to keep warm? An exhaust fan will vent water vapor, but it will also vent warm air, right?
I’d appreciate any advice. Haven’t been on BT in some time!
Replies
Condensation happens when moisture-laden warm air hits a cold surface and cools down below the 'dew point'. The higher the air temperature, the more water it can hold as vapour before it is saturated. Contrariwise, as air cools off, its maximum vapour content decreases.
The easiest way to avoid condensation it is to remove all sources of heat during cold weather, which is why most three-season cabins are drained and shut down completely for the winter. If you don't want to do that, you have to keep warm air out of contact with cold surfaces. That means, for instance, thermo-pane glass in your interior sashes and storm sashes or insulated shutters.
It also means you are right, you do have to close that attic hatch.
An easy way to do that is to nail some 2¾" casing to the ceiling around the hatchway, overlapping the opening by an inch all around. Cut a piece of drywall to fit in the hatchway. Paint the bottom of it to match the ceiling, and glue 2 or 3 pieces of 2" foam board to the top. Drop it into the casing 'frame' and you're done.
Your plumbing blockhouse will have to be ventilated if you leave the hot water tank on for the winter. The most energy-efficient way to do this is probably with an air-exchanger unit.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
Thanks, Dino -- yours was the only response to my problem. I've closed the hatch exactly as you described, except I used a piece of 1/4 birch ply instead of DW. Glued on 3 pieces of 2 inch pink foamboard. Tell me more about the heat exchanger for the cellar.You think heat should be OFF in the winter, right? We may overwinter this year, so that will not be an issue, but I imagine that the house has been be pretty dank in the winter without heat. Machined surfaces rust and some books get smelly. We will continue to ask around, see what people do. The heating contractors are very vague about what to do. Naturally, the fuel oil guy thinks we should leave some heat on.
The places out here that see this happen are those with the heat off and it is mostly in spring when whether is changing and the air is getting more humid. The interior walls are still cold but that humid air gets to them and condenses there. I have seen homes in March/April before heat is turned back on with water streaming down the walls. "Ventilation" just lets more of that moist humid air in.
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That sounds right -- a spring rather than a winter problem. So, if we aren't on the island, turn on some heat in spring? At any rate, in our area, is this a seasonal house problem. I've retired and wil be spending more time here, so maybe the problem will go away, ha ha.The cellar was inadequately sealed, no question. It would involve some awkward digging to get it right now. And not by me!
My bet? Once you close that attic damper and turn on a bit of warmth in the spring, it will be fine.
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Tell me more about the heat exchanger for the cellar.
What you want is an air exchanger. (A heat exchanger is a bit different, unless the marketing weenies have been dorking around with the language again while I wasn't looking....) Take a look at the FAQ answer below for a starter. I think the biggest issue you'll have to resolve for your installation is freeze-up of the condensate pan or the drain when no one's there. Possibly you could solve that with a length of gutter/downspout hot-wire hooked to a thermostat.
Air Exchanger Basics
With the emphasis on energy conservation and efficiency, new home construction can create a problem of indoor air pollution. Vapor barriers, thermal windows, weather-stripping and caulk have reduced or stopped fresh air from infiltrating and replacing stale air. Entering and exiting the house through doors isn’t always enough air changes. Cooking, aerosol sprays, cleaning agents, paints, and in some cases excess humidity if the house is sealed too tightly can create an undesirable environment. Keeping windows or doors open does not conserve energy. A device known as an air-to-air exchanger is used to recover heating or cooling and improve air quality.
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There are many different designs of air exhangers, depending on the manufacturer, but the principle is the same. Fresh air is drawn in from a port open to the outside of the building, and passed through a chamber, also know as the exchanger, that is surrounded by indoor air. Highly conductive metal or other materials removes the energy (heat) from the warmer air and gives it to the cooler air. The fresh air is then ducted into the house, and the indoor air is ducted to a port and expelled outside. Up to 80% of the energy can be exchanged. During the energy exchange, moisture (humidity) can condense into water. A drain pan inside the cabinet will allow the water to be collected for removal. If the unit is installed in the basement, a condensate pump might be used to eject the water outside.
Source: http://www.airexchangers.info/air_exchanger_basics.html
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
One option is to seal that cellar so no water gets in from the ground under it with a vapor stop.
Another would be to run a dehumidfier down there all winter. Residual heat from the pump would help keep it secure too.
But that can be expensive for electricity maybe, and unless you have somebody checking, it can trip off.
But I don't think your mildew is a winter problem. It stays pretty dry air in winter and mildew also needs heat to grow, so the growth happened in the spring, not through the winter.
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My dehumidifier in the basement used to ice up occasionally--don't know if that was when air was too cold or what, but you wouldn't want that happening in winter while you weren't there.
I've seen that, but my memory is that it is when it is hot and humid and the unit is working overtime
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