Fuel-saving Ideas for Old Heating Systems
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. The old-timers installed these during a time when the heating industry didn’t have 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. My guess is that a room thermostat starts and stops that circulator, and the boiler runs up to a set temperature limit, which is probably 180-degrees F.
Now, since the pipes and the radiators throughout your old house are so large, your heating system contains a lot of water. Your boiler has to bring that huge quantity of water up to temperature whenever the thermostat calls for heat, and that can waste fuel because when the burner starts and stops there's often a flywheel effect. 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 at just the right point so that the boiler puts into your house only the heat needed on that day. The water never gets hotter than necessary (remember, the coldest day of the year only happens once each year). Having a "reset" control is like putting cruise control on your heating system. The circulator will now run continuously and the temperature of the water leaving the boiler will ramp up and down to perfectly match the heat loss of the house. No more flywheel effect, and a nice savings in fuel.
And don't be concerned about the electricity needed to run the circulator continuously. Modern circulators don’t draw that much power, and the savings in fuel usually more than offsets this.
Smart Boilers Does your old house still have its original boiler, or maybe one from the '70s? If so, now is a good time to think about its retirement. Your older home has radiators sized for a time when open-window ventilation was popular, and insulation was still far off in the future. If you’ve insulated and updated your windows, your radiators are most likely larger than they need to be, which means they can warm you with cooler water. That makes them well suited for that outdoor-air reset control, but if you're thinking about a new boiler, ask your heating professional to talk to you about modulating/condensing boilers, or what professionals commonly call, "Mod-Cons." These smart boilers look at how much heat your old house needs and then modulate the fire to perfectly meet that need. This means that on milder days the fire inside your boiler will be smaller. A smaller fire means less fuel burned, and it's all automatic. The "condensing" part of the name tells us that these smart boilers also extract nearly all of the heat from the flue gases, bringing those gases to their dew point, and causing them to condense. That means that these boilers don't need chimneys, and that's great news if your old house also has an old chimney (and whose doesn’t?)
Any modern boiler will extract more heat than the old beast it replaces. The new boiler will probably also be smaller than the old boiler because you've insulated and upgraded your doors and windows. That means that the new boiler may not be compatible with the old chimney, and your contractor will probably talk to you about a stainless-steel chimney liner. If he does, listen because a mismatched boiler and chimney can produce dangerous carbon monoxide, but also ask about the new "Mod-Con" boilers. They're available in both gas- and oil-fired models, and they solve the chimney dilemma, while saving you a lot of money on fuel.
And while you're upgrading, consider this next option.
"Dry" Radiant Systems Until recently, radiant heating hasn't been a very viable option for old-house owners since installing a radiant system was like doing major surgery on the house. But now, "dry" radiant systems are more akin to an arthroscopic procedure. They're far less invasive, and well worth considering if you're renovating, or adding a room to your old house. Radiant systems save fuel because they warm people without heating the air. They work like the sun on a cold day.
A number of manufacturers are now offering dry (no concrete or gypcrete is involved) radiant systems that take away just a tiny bit of interior room height, while providing all the comfort and energy-saving benefits of hydronic radiant heating. Consider this option if you're laying a new floor. The dry system consists of a very thin plywood layer that supports thin aluminum tracks. Your finished floor hides the small-diameter PEX plastic tubing, which snaps into the aluminum tracks. The aluminum aids in transferring warmth from the water that flows through the tubes to the surface of your finished floor. Since the required water temperature is much lower than what you need for radiator heat, you save fuel. And yes, you can mix these systems with traditional radiators, as long as each system is on its own zone.
Another "dry" radiant option is to heat the floor from below with radiant tubing. I think the best way to do this 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. Again, the idea is to get the maximum heat transfer possible between the water in the tube and the floor, which leads to the lowest possible water temperature, and the greatest savings in fuel. "Dry" systems that just staple tubing to the underside of the floor call for hotter supply water temperatures, and while they do work, that also require more fuel. What you save on the plates you spend on the fuel, and considering that you only have to buy the plates once, they're a good investment.
If your old house has steam heat it's still possible to heat some areas with a radiant system, but you’ll need a heat exchanger to make the transition from steam to warm water back in the boiler room boiler before you pump the water through the tubing. This involves some engineering, and it's a good time to call in a heating professional that understands both steam- and radiant heating.
PEX and PEX/Aluminum/PEX pipe Okay, I've mentioned it a few times, and you may not know what I'm talking about, so here goes. PEX is an acronym that loosely stands for "polyethylene cross-linked." It's a super-strong, yet flexible plastic that more and more heating professionals are using for heating, plumbing, and even sprinkler systems nowadays.
PEX/Aluminum/PEX is a composite pipe that goes together in layers, like a sandwich, giving the pipe more rigidity for areas where that’s important.
Since either pipe bends, there are fewer joints to make (or to leak) and the material has proven itself reliable for nearly 40 years, both here and in Europe. And lately, the price of copper and steel has been soaring, making plastic an even more attractive alternative for all of us who need to move water from one place to another.
PEX-pipe manufacturers have also come up with some very innovative ways of connecting the plastic pipe to metal fittings, and to radiators, and none of these methods involve an open flame, so I think this type of pipe makes for a safer installation in any house, but especially in an old house, where the heating professional is often working in very tight quarters. Ask about it.
Ground-source heat pumps Dig down into the earth and you'll find the temperature to be pretty constant. A heat pump can reach down there with pipes and bring up whatever heat it finds, and then squeeze this into a hot concentration that's able to warm your home, especially if you're using one of those radiant systems I just mentioned. If you want to experience the concept of heat pumps, just stand near the outdoor exhaust of a window air conditioner. Feel the hot air? That's concentrated heat, coming from inside the house. You can feel the same thing coming out of your refrigerator. That’s why cats and dogs like to slumber there.
Window air conditioners and refrigerators squeeze the heat like water from a sponge and move it from inside to outside by using air at 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 the heat from the "sponge" into a heat exchanger that's inside your house. From there, the warm water flows through your new radiant floor. Radiant thrives on low-temperature water, and you save fuel as a result.
These systems are more expensive to install than conventional boilers, but they sure do save fuel, and the payback is getting shorter as the price of fossil fuel rises. It's also a greener way to heat your old house. Ask your heating professional about it.
Solar! Driven by European technology, solar heat (which is perfect for radiant systems and for heating domestic water) is getting noticed again. There are tax incentives to use these new panels in Europe, and I think we may see the same in America before long. There have been great improvements in solar technology since Jimmy Carter was president, making the new units so much more efficient. I recently visited the Viessmann facility in Germany and looked at a solar collector that was deliberately shaded so that it received only indirect sunlight. In spite of this, it was still producing an amazing amount of hot water. Which means that your new collector probably doesn’t have to be up on top of that gorgeous roof of yours.