Free heat

With the current weather, energy prices and economic climate, I’ve been looking for some ways to save on heating costs this winter. Everyone has written about saving money by lowering your thermostat, putting on a sweater, etc. but we’ve already done that, so I wanted to take a different approach. We have lots of items in our houses that generate heat, so I wanted to focus on keeping and using that heat, thereby reducing the amount of gas or electricity used by the furnace.

I like to be somewhat scientific with experiments like these, but I don’t have all the required equipment, and it’s hard to reproduce results with variables like the weather, so you’ll have to settle for anecdotal research and a little bit napkin-quality math.

The first thing I did was put that clear plastic sheeting on the windows. Our son’s room has two exterior walls and is the farthest room from the heater, so we have trouble keeping it warm. Right before putting up the barrier, it was 25 degrees (Fahrenheit) outside, the furnace thermostat was set on 68, and it was 60 in the room with the door shut. After installation, it was about 63 degrees in the room (after leaving time for the temperature to settle).

The next thing I did was address the heat lost when taking a shower. I haven’t measured my specific shower, but according to my research, a typical shower uses 30 gallons of water at 104 degrees Fahrenheit (40 degrees Celsius). That means every morning 30 gallons of hot water goes down the drain. What I do now is leave the exhaust fan off and the drain plugged. After I’m done with my routine I open the bathroom door and don’t drain the water until it cools to room temperature. If you’ll settle for some highly simplified calculations and assumptions, and if I remember what my high school physics class taught me about specific heat, we should be able to calculate how much energy we’re talking about. Those thirty gallons of water, cooling from 104 down to 68 degrees Fahrenheit (which is a drop of 20 degrees Celsius) release 9507 kilojoules into the room. That’s 2.64 kilowatt hours, or the equivalent of running a 1500 watt space heater for an hour and 45 minutes. At ten cents per kilowatt of electricity, that would equate to $.26 per shower. By the way, if anyone cares to corroborate or discredit my math, please feel free. Like I said, there’s some gross over-simplification, but the point is we’re keeping that heat in the house instead of sending it down the drain. In practice, the thermometer in the bedroom raises about 4 degrees after a shower.

The next approach took just a little bit of work, but I’m happy to have done it. The local Ace Hardware sells a device called a dryer vent diverter for just $7. It lets you vent your dryer into the laundry room instead of outside, and can be switched back and forth quickly. Our dryer is electric and located in our cold basement, so this device has worked great. A couple of things to keep in mind – NEVER use one of these with a gas dryer, and be warned that they are against code in some places. I ran a load of laundry as a test, and just one load through the dryer raised temperature in our 600 square foot basement from 58 degrees to 62 degrees, not to mention keeping the laundry room itself nice and toasty. From my research, electric dryers use around 4 kilowatt-hours per load, and most of that is heat being pumped outside. Additionally, since the dryer draws its air from inside the house and vents outside by default, every unit of air vented outside creates negative pressure in the house and needs to be replaced by sucking frigid outdoor air into the house through any gap in the house. So, if the air is dry and cold in your house, keeping that nice warm humid air inside works out great.

I’ll be looking for some more ideas, but so far I think I’ve captured the big ones.


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  3. Your shower idea may actually cool the house, not warm it. Consider the following.

    Assume that you have 2 zones for heating your house, upstairs and downstairs. You set both for 68 degrees. Your bathroom you do this trick with is upstairs, and the thermostat for upstairs is located close to the thermostat.

    So, you’ve now raised the temperature of the area close to the thermostat to 72 degrees, and the heat is shut off for upstairs. However, as you move away from the thermostat, the temperature drops off quickly. 10 feet away, it may be at 68 degrees. Your son’s room is holding at 63. In the time it takes the bathroom area to come down below 68, your son’s room may dip into the 50s. And that cooler air will sink down the stairs as well.

    Another test – in a large-ish room with a thermostat in one corner, check the temperature in the opposite corner while the heat is off. Place a lamp near the thermostat (on a table below it works best) and leave it on for a few hours. The temperature in that far corner will drop because the thermostat thinks the room is warmer than it really is, due to the lamp’s heat.

  4. Andy – you’re 100% correct. In my old apartment, I made the poor choice of placing my fish tank directly under the thermostat. Until I moved it, I couldn’t get the temperature in the apartment over about 58 degrees, no matter how high I set the thermostat. The fish tank created a warm tropical bubble over itself, making the thermostat believe the apartment was a balmy 78.

    That being said, with proper air circulation (i.e. running the ceiling fan in the master bedroom) the heat redistributes OK. Point well taken. My goal was to keep heat inside the house, but if it’s not getting where it needs to be, that doesn’t help much.

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