This article was originally published in the September/October 1993 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online September/October 1993
Hookups--Alternative to Backdrafting
Reader Greg Roody wrote regarding possible backdrafting of a boiler which makes year-round hot tap water, when a whole house fan runs (Whole-House Fans and Oil-fired Furnaces, May/June '93, p.4). You noted that outside air must, of course, be able to flow freely into the house when the fan runs.
In a previous house, Roody had successfully used an interlock to prevent the fan and boiler from running simultaneously. That's fine, but I can offer a simpler solution which also can save the Roodys money on boiler fuel: Just switch the boiler off almost all the time outside the serious heating season. Then if the boiler needs to run to heat tap water when the fan would normally also be on, such as a short time on a summer morning, simply switch off the fan while the boiler fires. Then shut the boiler off and the fan back on if it's still needed. Virtually all of the time when the fan needs to run, the boiler should probably be off anyway.
By the way, Roody mentions being awakened by smoke alarms when his earlier fan caused boiler exhaust backdrafting. I would ask why the heck his boiler was firing in the middle of the night anyway in the cooling season. We know the answer: The boiler's aquastat called for heat, whether or not anyone ran hot tap water. The solution is to simply not let it fire, except before and perhaps during times when hot tap water is actually needed (depending on boiler heat storage capacity). In my part of eastern Pennsylvania, we call this arrangement a summer-winter hook-up.
A cheap timer might be a sensible option, but I'd rather choose when the boiler will run and then be shut off each day. That way we can absolutely minimize boiler running times and still get hot water whenever we need it. We also try to wait to run discretionary hot water uses such as our dishwasher until after the boiler is shut off and after we've had our morning tubs. That way the dishwasher, for example, will not cause the boiler to fire again but will suck heat from the boiler after it's shut off, and will put that heat to use.
Penn T. Clissold
Editor's Note: This solution works fine as long as occupants are willing to take the time to figure out their hot water needs and coordinate them with boiler and fan operations. Of course, just switching the boiler off outside the heating season constitutes an manual interlock.Someone has to make the effort to switch the boiler on and off manually, which often means getting up to a cold house to turn it on in the morning! Nevertheless it is true that the most energy-efficient controls are manual, provided enlightened individuals are operating them. One must evaluate each application to decide how much control to give the occupants versus some automatic scheme.
Insulating Knob and Tube
My company is planning a pilot low-income weatherization program in Maryland, similar to our two WarmChoice programs already operating in Ohio and Pennsylvania. We have run into problems with Maryland's treatment of knob-and-tube wiring and are looking for ways to effectively insulate homes with this type of wiring. I have an article from Home Energy detailing how California was dealing with the National Electrical Code's edicts on K&T (see Knob-and-Tube Wirings Hang-ups, May/June '91, p.7). Have you received any innovative responses on how to deal with such houses? I would appreciate any references you could give me on how others are handling this situation.
Catherine M. Muller
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