Replacing the Heating System in an Old House
Steam radiators and spotty insulation make for a challenging HVAC problem.
A big house near Boston is posing big questions for its owner when it comes to upgrading a one-zone steam-heating system.
Writing in a Q&A forum post, kcchernak (we’ll call him KC), explains that the 5000-sq.-ft. house, built in 1892, has living space on three levels, including a finished attic, and is heated with a gas-fired steam boiler that was installed just six years ago.
Heat is controlled by a Nest thermostat with comfort sensors that help regulate heat in specific areas of the house. KC is in the process of installing air conditioning and making a few other upgrades with some, but not all, of the interior walls open.
“Aside from being single-zone and the drawbacks of that, the current radiator system clangs quite a bit and we have some leaky radiators that probably need to be replaced,” KC says. “We’re paying quite a bit for natural gas right now and we’re a bit high on electricity, too. It’s also worth noting that we know we have some insulation gaps and are working to remedy those in the next several months as well.”
KC has spoken with several HVAC contractors who suggest that he add heat pumps to the system, or replace the steam boiler with a wall-hung boiler and a forced-air distribution system.
In addition to attaching a quote for a new HVAC system, KC also posts a recent gas bill of $993 and electric bill ($239) for a total energy charge of more than $1200 for the month.
“I’m wary of making a total heating system switch, but maybe I shouldn’t be,” KC says. What’s the next best step? That’s the topic for this Q&A Spotlight.
Those ideas won’t work
Paul Wiedefeld doubts that the contractor proposals for installing air handlers and condensers will be successful. “The hydronic air handlers are useless for your situation and can be dismissed outright,” he says. “Unless the air-handlers are spec’d for lower water temperatures, a ‘wall-hung water-boiler unit’ (a modulating, condensing boiler, wall-hung or otherwise) will not be more efficient than the existing steam, plus they’ll require pumping and blower energy the steam does not need.”
Wiedefeld doesn’t understand why contractors are making those suggestions, unless their only goal is to sell KC a new boiler. And even then, he would not need a condensing boiler.
Instead, Wiedefeld recommends installing a heat pump, which would cost about the same as central AC.
If the heat pump meets the heating load, the problem is solved, Wiedefeld says. If it doesn’t meet the heating load, he would have several choices, including:
- Electric resistance backup integrated into the air handler, which is dirt cheap to install but expensive to run.
- A furnace using the new ductwork (a gas/electric hybrid set up). This is more expensive to install but usually cheaper to run than the electric resistance and potentially cheaper than the heat pump at some outdoor temperatures.
- Keep the steam as the backup.
One problem with keeping the current steam system for backup is the network of pipes it requires in the basement, KC replies. “If we ever want to finish our basement, we’ll need to consider major modifications or ripping it all out,” he says.
Start with a Manual J
The place to start is with a Manual J calculation, Akos advises. This process to determine heating and cooling loads should be carried out by an independent HVAC engineer.
“The chances of your place having a 6- to 7-ton cooling load is pretty much zero, at best it is about half that,” Akos says. “The simplest AC retrofit in older houses is high-velocity as you can fish the pipes through existing walls. The equipment is not cheap but would be less work than trying to hide standard ducting.”
Also make sure to keep the HVAC out of the attic, he adds, because this would result in cooling costs by 25% while “adding a couple of big air leaks to an already leaky older house.” A good compromise is spray-foaming a knee wall section and installing the equipment there.
Finally, Akos asks whether the current steam radiators are one- or two-pipe varieties. A one-pipe system, in which steam and condensate both use the same supply pipe, are more difficult to convert to hydronic heat and best left as is. (The radiators, KC says, are the two-pipe variety).
(As for keeping the HVAC system out of the attic, KC replies, it’s too late for that—the area is already heated and it’s where the guest room and family hangout area is located. KC is planning to add AC to the attic as well.)
A heat pump may not be the answer
Akos is not confident that a heat pump is worth it for such a large and leaky old building. “You would have to oversize to such an extent to heat the place that cooling would suffer,” he says. “Maybe if you are looking to do some significant envelope improvements it can be made to work, but somebody should do some calculations to figure it out.”
In fact, without undertaking major energy improvements it’s hard to make a house built in the 1890s comfortable with anything other than radiators or floor heat, Akos says.
“If you are in an area with a lot of steam heat, I’m sure you can find a decent old steamer to take a look at your setup and fix your clanging and leaks,” Akos says. “Since you already have a newish steam boiler, any kind of major rework or replacement doesn’t make financial sense.”
He also makes these points:
Adding a heat pump would cost more than a simple AC system, but it would make sense financially if the steam system is powered by oil or propane. It’s harder to get the numbers to work when natural gas is the fuel, Akos says, unless the homeowner is looking to eliminate fossil fuels from the mix entirely.
“I guess with good design you can make a forced-air system work as well,” Akos adds. “I have yet to see this with older houses around me, though. Old, leaky, forced-air houses tend to be pretty uncomfortable. Once the place is air-sealed and windows replaced, it can definitely be made to work, though.”
Planning for the AC system
Given KC’s Boston location, where cooling loads are not extreme, Akos thinks a modulating system may not be worth the extra money, unless KC is aiming for a quieter outdoor unit. He thinks a “right-sized, two-stage outdoor unit with a variable-speed ECM air handler is probably the best value.”
But Mike Ferro, also from the Boston area, thinks that KC might want to opt for a high-efficiency system. Ferro runs the air conditioning enough months of the year that the efficiency gains generate a quick return on investment. He suggests at least a 16 SEER outdoor unit that is multi-stage or variable-speed.
“Your contractor is proposing a bargain basement single-speed outdoor condenser that I imagine (it’s not evident on the quote) is paired with a bargain basement single-speed PSC blower-type indoor air handler from Goodman,” he says, referring to the written quote that KC has provided. “There are better manufacturers and options in this space. Carrier makes some great equipment and should be available to your contractor at a local wholesaler.”
He suggests checking the MassSave website for incentives on higher-efficiency equipment, which may make it easier to invest in the better equipment.
“Lastly,” he continues, “regarding the heat pump option, the condenser is the most expensive piece of equipment in the proposed system and it’s not an easy thing to swap later.”
Get those energy bills down now
Given the sky-high gas and power bills that KC is paying, Wiedefeld and others urge KC to start by eliminating as many air leaks in the building enclosure as possible.
“Spend some time on this site reading about air-sealing,” AMorley says. “In a big old house, fixing insulation gaps alone won’t do the trick. Air-sealing critical areas can really improve comfort. Since you are mid-renovations, you have a great opportunity to do some air-sealing work that isn’t as easy once you are done renovating.”
He continues, “Try to bring in an energy auditor or weatherization contractor to come and do a blower-door test and air-sealing assessment.”
Our expert’s opinion
Jake Staub had this to say:
KC’s plight is not unusual. That said, it is best to formulate a deliberate plan of attack before attacking. While it is true that even the best plans do not survive first contact with field conditions, sound strategic vision goes a long way toward tilting the outcome in a favorable direction.
Before getting into the details, I will note that residential steam systems were solutions born of a bygone era when coal was the primary source of energy and opening windows was the primary means of temperature control. At the time, a central-heating system of any form in a single-family home was a revolution and a major victory for comfort and convenience. While relatively simple, steam systems are robust and were by-and-large designed and installed by people who had a considerable understanding and appreciation for the natural world. As a result, steam systems require sophisticated people to maintain them now just as they did way back when. One good marker for identifying such people is whether or not they have a copy of Dan Holohan’s The Lost Art of Steam Heating as a working reference.
As far as KC’s steam system is concerned the gripes are as follows: 1. single-zone control, 2. clanging pipes, 3. leaking radiators, and 4. high natural gas utility bills. All of KC’s gripes are indicative of a steam system in need of modernization. Fortunately for KC, New York City, the country’s center of gravity for steam heating systems, has devoted substantial resources for steam system modernization. One excellent report published by Energy Efficiency For All is “Clanging Pipes and Open-Window Steam Systems for the 21st Century.” The brochure version of the report released by the NYC Retrofit Accelerator is called “Smart Steam Heating Upgrades.”
KC’s boiler upgrade in 2016 was the most substantial step toward steam system modernization. The report and brochure referenced above describe the remaining steps to complete the modernization. This should substantially address KC’s heating system gripes. According to the referenced report, heating energy savings on the order of 20% can be expected. Simple payback period is estimated at eight years.
Given social pressure to do more to reduce energy consumption, there is usually a need to know whether a greater reduction in energy consumption could be made. Appendix E in the report referenced above describes hydronic conversions for small buildings with two-pipe steam systems. Typically, these types of conversions are cost-effective and result in heating energy savings on the order of 40%. Hydronic conversions also go further in addressing the balance of KC’s gripes outlined above. Do not read Holohan’s book if a hydronic conversion is on the table as a viable option. Holohan’s enthusiasm for steam systems is so infectious it is likely that the option to execute a hydronic conversion will be summarily dismissed.
Assuming the benefits of hydronic conversion are too attractive to pass up, traveling that path is consistent with a general improvement effort that includes building envelope upgrades now or over a period of time. Steam systems are more rigid where sizing is concerned. Steam systems are sized for connected radiator sizes rather than building loads. As building envelope performance improves, the gulf between original steam system size and required steam system size grows and tends to aggravate problems related to comfort and economy. At some point, the steam system would require a complete rework, which would not be economical relative to a hydronic conversion.
As far as the cooling side of the problem is concerned, evaluation of a dual-ducted heat-pump product made by Ephoca called All In One (AIO) Wall Mounted is recommended. The dual-ducted heat-pump equipment has been used extensively in Europe to incorporate cooling into older buildings in an architecturally sensitive manner. Due to its success there, the equipment has migrated to North America via Ephoca and an alternative manufacturer called Olympia Splendid. There is Ephoca documentation showing an accessory hydronic coil for AIO specifically meant for hydronic conversion applications. If the accessory hydronic coil is available, AIO would be a valuable asset in the completion of a well-integrated hydronic conversion with air conditioning upgrade.
In summary, given the amount of consideration required to successfully execute major building rework, it is best for the planning process to occur well in advance. Fortunately for KC, NYC has laid much of the groundwork to address his gripes. Per the NYC-sponsored planning documentation referenced above, a modest heating system upgrade would amount to the modernization of the existing steam system. The most aggressive heating system upgrade would amount to the hydronic conversion of the existing steam system. In either case, a dual-ducted heat pump equipment type is an asset when there is a requirement to incorporate cooling into older buildings in an architecturally sensitive manner.
Originally published on GreenBuildingAdvisor.com. Scott Gibson is a contributing writer at GBA and Fine Homebuilding magazine. Jake Staub is an aerospace engineer and chief technical officer at Ripcord Engineering in Portland, Maine. Reader comments may be edited for clarity. For a look at the complete thread, use the link at the top of this column.