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Cool Ways to Heat Old Houses

Advances in technology are helping to make old houses more energy efficient in an unobtrusive way. By Dan Holohan

    ModCon boilers make more efficient use of fuel by modulating the temperature of the boiler flame, while condensing heat from exhaust gases so that they don't need to be vented out a traditional chimney. Photo Courtesy of Heat Transfer Products, Inc.

    ModCon boilers make more efficient use of fuel by modulating the temperature of the boiler flame, while condensing heat from exhaust gases so that they don't need to be vented out a traditional chimney. Photo Courtesy of Heat Transfer Products, Inc.

    Your house is old and gorgeous, as are those wonderfully ornate cast-iron radiators, but these days, energy prices are anything but old-fashioned. Fortunately, there are new ways to conserve fuel without ruining the classic look of old radiators. Some of these products may involve significant changes to a heating system, but all of them work behind the scenes so that your home keeps its historic appearance. Only your fuel bills will notice the changes.

    Take Control
    If you have an older hot-water system, it probably once ran on gravity. The hot water rose from the boiler and the cold water sank from the radiators, creating a Ferris Wheel of natural convection. Originally, these systems were installed before there were circulating pumps to move the water through the pipes. If your house has a gravity system, someone has probably added a circulating pump to it by now. A room thermostat generally starts and stops the circulator, and the boiler runs up to a set temperature limit, usually about 180 degrees Fahrenheit.

    Because the pipes and radiators in an old house are large, the heating system contains a lot of water that has to be heated every time the thermostat goes on. That wastes fuel because even after the circulator stops, the radiator pipes are still full of hot water and continue to heat the house. You can solve this problem and save energy by getting an outdoor-air reset control for your system. This control monitors the outside-air temperature and then sets the boiler water temperature accordingly to produce only the amount of heat needed on that day. The water never gets hotter than necessary.

    Having a reset control is like putting your heating system on cruise control: The circulator runs continuously, and the temperature of the water leaving the boiler ramps up and down to match the heat loss of the house perfectly with no more wasted fuel. As for electricity, the circulator is so efficient that the fuel savings will more than offset the cost of the power used.

    Get Smart
    Does your old house still have its original boiler, or maybe one from the 1970s? If so, now is a good time to think about retiring it. Older homes have radiators sized for a time when open-window ventilation was popular and insulation was uncommon. If you’ve insulated and updated your windows, your radiators are most likely larger than they need to be, which means they can warm the house with cooler water, making them well suited for an outdoor-air reset control. If you’re thinking about buying a new boiler, ask a heating professional about modulating-condensing boilers, also called Mod-Cons. These smart boilers sense how much heat an old house needs and then modulate the fire accordingly. On mild days, the fire is smaller and burns less fuel. The condensing part of the name stems from the fact that smart boilers extract nearly all of the heat from the flue gases, bringing them to their dew point and causing them to condense.

    As a result, these boilers don’t need chimneys—a plus for an old house. Any modern boiler will extract more heat than the old beast it replaces and probably be smaller, too. But if the new boiler vents through an old chimney, it’s unlikely to be compatible, and your contractor will probably recommend installing a stainless-steel chimney liner. If so, heed the advice because a mismatched boiler and chimney can produce dangerous carbon monoxide. Using the new Mod-Con boilers, which come in gas- and oil-fired models, sidesteps the chimney dilemma because they can be vented out a foundation wall.

    Try Dry Systems

    The latest generation of radiant-heating installations, sometimes called dry systems because they eliminate setting lines under a wet bed of concrete, use small-diameter hose snapped into a prefabricated base, such as these thin plywood panels. Photo: Watts Radiant

    The latest generation of radiant-heating installations, sometimes called dry systems because they eliminate setting lines under a wet bed of concrete, use small-diameter hose snapped into a prefabricated base, such as these thin plywood panels. Photo: Watts Radiant

    Until recently, radiant heating hasn’t been an ideal choice because installing a radiant system required major surgery on an old house. Now, however, dry radiant systems (so called because no wet concrete or gypcrete is involved) are more akin to an arthroscopic procedure. They’re far less invasive and well worth considering if you’re renovating or adding a room. Radiant systems save fuel because they warm people without heating the air, like sitting in the sunshine on a cold day.

    A number of manufacturers now offer dry radiant systems that take away just a bit of room height, while providing all the comfort and energy-saving benefits of hydronic radiant heating. It’s a good option if you’re laying a new floor. The dry system consists of a thin plywood layer that supports narrow aluminum tracks. Your finished floor hides the small-diameter PEX plastic tubing (see sidebar at left), which snaps into the aluminum tracks. The aluminum helps transfer warmth from the water that flows through the tubes to heat the surface of the finished floor. Because the required water temperature is much lower than that for radiator heat, you save fuel, and yes, you can mix these systems with traditional radiators as long as each system has its own thermostat.

    Another dry radiant method is to heat the floor from below with radiant tubing. Some experts believe the best method is to attach aluminum heat-transfer plates to the underside of the floor and then snap the PEX tubing into the channels on the plates. The idea is to get the maximum heat transfer possible between the water in the tube and the floor for the lowest-possible water temperature and the greatest fuel savings. Dry systems that staple the tubing directly under the floor without using a plate need a higher water temperature, which burns more fuel. Even though the plates add to the cost of installing a dry system, you’ll only need to buy them once, and over the long haul they’ll more than pay for themselves with fuel savings.

    If your old house has steam heat, it’s possible to heat some areas with a radiant system, but you’ll need a heat exchanger for your boiler to make the transition from steam to the warm water that is pumped through the tubing. Some re-engineering of the system is involved, so get a heating professional that understands both steam and radiant heating.

    Go Underground
    Dig deep into the earth, and you’ll find the temperature is pretty constant. A ground source heat pump can reach down there with pipes and bring up whatever heat it finds to warm the water circulating in the pipes. The pump works especially well with dry radiant heat. To experience the concept of a heat pump, stand near the outdoor exhaust of a window air conditioner. Feel the hot air? That’s concentrated heat collected from inside the house.

    Window air conditioners wring heat from the air like water from a sponge, and move it from inside to outside using air as the transfer medium. Ground source heat pumps gather the heat from deep in the ground with a similar sponge (this one in the form of flowing water) and then squeeze out the heat into a heat exchanger inside the house. From there, the warm water flows through the radiant floor. Radiant heat thrives on low-temperature water, so you save fuel as a result. Although more expensive to install than conventional boilers, these systems are paying for themselves sooner as fuel prices rise, and proving to be a greener method — in more ways than one — for heating old houses.

    Think Solar

    In a closed-loop system, a ground source heat pump circulates water or antifreeze through pipes buried in the earth. In winter, the system extracts heat from the relatively warm temperature of the earth (about 50 degrees Fahrenheit); in summer, the system reverses to provide cooling for the house. Photo: International Ground Source Heat Pump Association

    In a closed-loop system, a ground source heat pump circulates water or antifreeze through pipes buried in the earth. In winter, the system extracts heat from the relatively warm temperature of the earth (about 50 degrees Fahrenheit); in summer, the system reverses to provide cooling for the house. Photo: International Ground Source Heat Pump Association

    Thanks to European engineering, solar heat, which is perfect for radiant systems, is getting noticed again. Since the 1970s, solar technology has improved tremendously, making the new units so much more efficient. I recently visited a solar-equipment manufacturer in Germany where a solar collector was deliberately shaded so that it received only indirect sunlight. The device was still producing an amazing amount of hot water even in the shade, a great feature if the only thing stopping you from going solar is that you don’t want to spoil the look of your gorgeous old roof.

    Published in: Old-House Journal November/December 2006

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