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should we close off attic vents in winter?
19 November 2005


Q. We live in a beach cottage with some insulation in the attic. I can see by flashlight that there are gaps of coverage particularly at the eaves. My question is, aside from having better and more insulation, should one block off the roof vents during winter months? Would this help in any way? We are seniors and utility bills are getting to us as we heat with propane fired hot water system. Also the water heater is attached to the boiler so would it make any sense to have a “point of use’ water heat er for our shower? That is one sore point we have with this type of water heating in the winter as we have a cold well water supply to the boiler.

A. Only if you had absolutely no insulation would I recommend blocking a roof vent. Heat goes straight up, as you know, and the function of insulation is to slow the thermal movement as close to a stop as posible, keeping the heat in the house. Roof vent s have another very important function that most folks generally don’t consider when they think about roof or attic ventilation and that is the venting out and away from the building of moisture that warm air holds more than cool or cold air can. If you close off the vents then heat the house up to a tolerable 68ºF or 70ºF, the moisture that ends up in warm air from normal living,washing and cooking inside the house will migrate to the uppermost regions of the structure to find building materials signi ficantly cooler than the household temperature and condense. I have seen the undersides of improperly vented roofs glisten wet with condensed household moisture. I was once called to nice home locally where the owner recently had a new roof installed an d, as the weather cooled, decided to block off the roof vents. He went up into the attic in mid-February or so to find the roof boards soaking wet and anything he had stored up there-- luggage, books, golf clubs etc-- covered in white and green mildew. He called his roofer claiming the new roof was no good and he was hopping mad about it. I had to tell him it wasn’t the roof that caused his problem but the plastic sheeting he’d stapled over the gable vents. He didn’t believe me for almost a week until his heating contractor told him the same thing. My advice to you is to invest as much as you can in upgrading the insulation in the attic and leave the vents open.

Your well water delivers water to your boiler to be heated for hot water use at sinks, tubs and showers at the exact same temperature in July as it does in January. Water comes out of the ground around 55ºF or so regardless of outside air temperature. So gallon for gallon of hot water that comes out of the boiler is the same year round as far as propane usage for water heating is concerned. It takes the same amount of energy to raise the water temperature from a cold 55ºF to a hot 120ºF or higher regard less of season. Now, a point of use water heater for the shower would indeed deliver instant hot water to that shower piping hot but as I’ve written before by the time you compute the cost of the point of use water heater plus installation against what you’ve already got you’ll learn it’ll be a long distant day in the future before you realize any savings-- if ever. So if money is a concern my advice to you is don’t do it. The solution to lowering your propane use is insulate insulate insulate. Weathe rstrip doors and windows and bundle up.

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