Updating an Antique Heating System
A Maryland homeowner loves his historic house, but whopping heating and cooling bills has him looking for alternatives
The multistory brick home in Frederick, Maryland, is an "amazing property that deserves to be lived in and preserved," says a Green Building Advisor reader who calls himself Joe Schmo. Its Achilles heel is a heating and cooling system that costs thousands of dollars a year to operate.
The system consists of an oil-fired boiler that supplies radiators with steam, two air-source heat pumps that provide air conditioning, and back-up electric resistance heat. There's a 4-ton unit in the basement for the first floor, and a 3-ton unit in an attic that serves the second floor.
The 4,200-square-foot house is "surprisingly tight (relative of course), considering its age," Schmo writes in a Q&A post at Green Building Advisor, "but my objective is to use the steam radiator/oil system only as a back up due to the large costs and safety concerns associated with using it."
Adding insulation in the exterior walls doesn't look like an option, although Schmo may add insulation in the attic. But more efficient heating and cooling equipment is definitely on his list. Schmo plans to replace the older air-source heat pumps with new 5-ton models.
"In this day and age, I think a well-distributed, high-efficiency system — e.g. dual unit, dual zone heat pumps — should be able to save us money over the oil-fired boiler and electric back up, no?" Schmo writes.
His question is the topic for this Q&A Spotlight.
Get natural gas if you can
Kevin Dickson recommends that Schmo look into a conversion from oil to natural gas, especially if there's no way of adding insulation in the walls. "Gas looks to be cheaper than conventional heat pump heat for now and many years to come," Dickson writes.
He suggests that Schmo take a look at an online forum called HeatingHelp.com. The site has thousands of threads, and whole sections devoted to steam and oil heating.
Schmo says that natural gas is not currently available at the house, and even if it were, it would mean combustion products inside the house, which he'd like to avoid if possible. But if saving money is the object, converting to gas is indeed attractive.
"If your house is on the gas grid, the cheapest solution would be to install a conversion burner," writes Dana Dorsett, "which would cut your source-fuel BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. cost by half. The efficiency as a system may still be pretty low, though — some steam systems operate at less than 50% net efficiency."
Dan N. adds that gas suppliers can sometimes be convinced to run new lines to neighborhoods where demand is high. "I know they did in my parents' neighborhood after enough people on the block made a commitment to convert to gas," he says, "but it takes someone on the block to get people interested in change. Something to think about."
Sharpen your pencil and do the math
Dorsett would start with a heat load calculation. Otherwise, he says, Schmo won't know whether the heat pumps he has in mind will do the job.
On a mid- or late-winter oil fill-up, look up the number of heating-degree days that occurred since the last fill, Dorsett says. That information should be available from a website called Degree Days.net. "Then we can figure out from fuel use against degree-days and the boiler's efficiency approximately how much heat pump it takes to get you there," he says.
With Schmo reporting extremely inexpensive electricity (5.4 cents per kWh vs. $4.30 a gallon for fuel oil), Dorsett says he'd save money by replacing the steam heating system with electric resistance heat.
Electricity at $0.054 per kWh is $15.91 per million BTU (MMBtu), Dorsett writes. If Schmo were paying the Maryland statewide average of $0.1348/kWh, it would be $39.51/MMBtu.
A ducted heat pump system with an average coefficient of performance (COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. ) of 1.5 would mean heating costs of $26.34/MMBtu, he adds, while a "better class" ductless minisplit with a higher COP could reduce costs to about $10/MMBtu.
At the price Schmo is paying for oil, and assuming a burner operating at an efficiency of 85%, it costs $36.66/MMBtu, "That's barely cheaper than resistance-electricity at the average Maryland price."
"In reality with the standby and distribution losses of the steam system, it would probably be slightly cheaper to go with resistance electricity at the state average price," Dorsett says. "With 5-cent electricity you'd be paying well under half for heating than you are with oil. At a more typical 70-75% net operating efficiency, your output per gallon is really more like 100,000 BTU/gallon, or 10 gallons/MMBtu, for a heating cost of about $43/MMBtu."
Zoned heating can help, too
Dan N.'s experience with an old house in New Jersey of roughly the same size as Schmo's also suggests that zoned heating can lead to big savings.
Dan N. swapped his oil boiler for a natural gas unit, and increased the number of heating zones from one to five. "I heat the rooms I need to heat, when I need to heat them, and the smaller loops are a lot more efficient and heat a lot more evenly," he says. "When the house was on one loop, the last few rooms on the loop were barely warm and the first few rooms were hot."
His heating bills went from as much as $6,000 a year to less than $1,000.
Sell the house and move? Nope.
Faced with daunting heating bills, Schmo could always sell the house and buy something less expensive, AJ Builder says. Or consider a ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures. that, while expensive, might be eligible for subsidies. "Did you know that your utility bills were going to be $20,000 annually when you purchased?" he asks. "And you figured when you purchased that somehow after the fact you could add in the cost of changing to heat pumps?"
According to AJ Builder, whole house air-source heat pumps are not going to save Schmo a lot of money. "Your best way to save would be to sell that home and buy something that has lower costs," he advises.
That's not on the table, says Schmo. "I could live in a shipping container, too, but I won't," he replies. "I could do a lot of things, but selling a dream home that I just purchased is hardly a prudent move... It is an historic property that has stood many times longer than most houses being built today will. It's a challenge, but one worth attempting, considering it really is a matter of transitioning it from 19th century thinking to today's."
Schmo is a little surprised at some of the suggestions he's been given at GBAGreenBuildingAdvisor.com. "For instance, we might able to install two new high-efficiency 16-SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. air-source heat pumps and a rooftop solar array for less than or about the same as a geothermal system and reduce both the electric expense overall as well as fossil fuel usage," says Schmo. "I guess my question is whether anyone has a better idea."
Our expert's opinion
Here's what GBA technical director Peter Yost had to say:
It certainly is a beautiful historic home. And I bet all that heat that has been pumped through the building enclosure all these years is a significant part of its drying scheme.
If there was ever a candidate for a comprehensive, detailed, building performance audit, this is it. It's very tough to make sound recommendations when we don’t know the real performance properties of the building, especially when possibilities mentioned involve both mechanical (space conditioning system) and building enclosure (attic insulation) options.
I can't tell you the number of older homes with performance problems I have been asked to look at where a building performance audit before the energy upgrade would have resulted in a completely different and more successful energy upgrade.
And just about number one on the problem list is adding attic insulation without resolving sources of moisture and big air leaks connecting the attic and basement. I can’t of course say this applies to this home given just the two photos, but it also would not surprise me to find sources of moisture in a stone foundation and either a dirt or concrete floor without capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. break or vapor barrier and multiple full-building height chases.
In any energy upgrade, both mechanical and building enclosure improvements should be part of a quantitative evaluation. But just as important as assessing the home’s energy performance is evaluating the way it handles moisture and this hygrothermalA term used to characterize the temperature (thermal) and moisture (hygro) conditions particularly with respect to climate, both indoors and out. approach (combined heat and moisture) is exactly what a whole building performance audit entails.
So, include both building enclosure and mechanical options in any energy upgrade and evaluate both heat and moisture flows to ensure that the energy upgrade solution includes and manages moisture as well.
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