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Old-House Online » Old-House Tips, Restoration Stories, & More » Interiors & Decor » Do’s and Don’ts for HVAC Retrofits in Old Houses

Do’s and Don’ts for HVAC Retrofits in Old Houses

Ductless systems, small output vents, through-the-wall A/C, efficient furnaces—it’s all good news for old-house owners.
By Dan Cooper

    The wall-mount unit by Mitsubishi Electric offers ductless heating and air conditioning in a space-saving unit that is both easy to install and less obtrusive than window units.

    It wasn’t until the 19th century that most Americans were able to afford the technology that permitted a heat source to be located remotely in the house, rather than in the inhabited room. The device was the coal-fired, gravity hot-air system, which directed heated air upward through a series of ducts into living spaces. Around the turn of the 20th century, steam heat replaced those systems. While steam systems were superior from a technological point of view (until the emergence of forced hot air), people now had to deal with a hulking iron mass in each room (the radiator), which was typically placed where it would have been nice to put the credenza.

    Things remained unchanged for the better part of a century. Today, those of us retrofitting an old house with a contemporary heating system have options that dramatically reduce the system’s visual and functional impact on rooms—and they are highly energy efficient, besides. At the same time, of course, air conditioning is no longer viewed as a luxury in much of the country, so integrated HVAC (heating, ventilation, air-conditioning) systems are on their way to becoming the norm.

    Today’s smaller systems, like Rinnai’s tankless water heater, take up much less room than their predecessors.

    Today’s smaller systems, like Rinnai’s tankless water heater, take up much less room than their predecessors.

    Until recently, the challenge in conveying climate-controlled air throughout a building was the size of the metal ductwork, typically an invasive 31⁄4″ x 10″. Ducts were placed in stud cavities and between floor joists. Modern systems offer round ducts that are merely 2″ to 21⁄2 ” in diameter. These can be snaked through more constricted areas, similar to the way plumbing and electrical lines are fed. The wholesale demolition of old plaster is history.

    An additional benefit to these newer systems is the size of the openings, or registers, in the room. They are small, flanged disks available in wood species that match flooring, or they may be painted to coordinate with wall and ceiling treatments. Of course, the outlet can always be fitted with a vintage-style ornamental register.

    Regarding the “business end” of HVAC systems, gone, too, are the huge, multi-armed, asbestos-shrouded “octopus” furnaces that loomed in the basement. High-efficiency furnaces exhaust through a plastic pipe let through the foundation wall, eliminating the need for brick chimneys. (A preservation-minded aside: What will happen when we no longer need the chimneys, but are faced with the expense of preserving or rebuilding a crumbling ornamental one that’s part of the history and style of the house? Many will be disassembled and roofed over.) The new furnaces are much smaller.

    Unico’s flexible tubing system fits into the existing cavities of an older home and eliminates the need for extensive remodeling.

    For cases where central air is hard to install—as when an old house has steam or hot-water heat and no ductwork—new A/C units provide an alternative to the unwieldy window appliance. (Not only do these look horrible from the street, but they also block some light, and they usually need to be removed and re-installed seasonally.) Several manufactures offer wall units that allow you to select which rooms are to be air conditioned, avoiding central A/C. The devices are visible, yes, but in their size and efficiency—and because they don’t block windows—they are certainly an improvement.

    Location, Location, Location

    New technology allows you to place HVAC registers almost anywhere, a good thing for retrofitting in an old house. If you are in the midst of renovation, it’s still important to think ahead before you situate ducts, registers, etc. What are the eventual locations of breakfronts and bookcases, sofas and other large furnishings? For walls and ceilings, keep symmetry in mind: How will the outputs or registers look once they are incorporated into a wallpaper frieze?

    For old-house-friendly HVAC resources, see the Products & Services Directory.

    Published in: Old-House Interiors November/December 2011


    Dawn mohrbacher November 23, 2011 at 12:46 am

    I enjoyed this article particularly because I was curled up hiding in the fourth floor of our Victorian hiding from the contractors swarming below like busy little ants. You see….we were in the middle of installing modern heating in our Victorian….timely huh? I enjoyed the article but would have liked to see it go one step further to show how to hide the addition of modern systems. We spent a great deal of time on that subject in our retrofit so instead of seeing the big plastic white box over a window in our house you’de see a pelmet in which the box is hidden, or a turn of the century secretary or amoire in which the systems are hid. For me, the plastic box is a huge eyesore…akin to baseboard heating. If others want to see how to hide the stuff, we would be happy to share!

    David Conwill February 1, 2012 at 5:24 pm

    Finally, an answer for the dilemma I have faced with our octopus-come-forced-air system! It really needs to have the cold-air returns and heat ducts swapped, but I didn’t think there was a cost-effective way to do it.

    Now, if someone would just come up with a way to do a high-efficiency retrofit of my coal fireplace into a sealed gas unit, I’d be all set.


    Ken - the OldHouseGuy October 12, 2012 at 4:35 pm

    I love my 1942 gravity Octopus furnace and it still works great (converted to oil from coal). I even have the instruction manual that shows how to start the coal on fire. Check out the picture

    I realize its days are numbered. Oil is expensive and the furnace is only about 50% efficient. I plan to install a new high efficiency gas furnace behind my antique furnace next year. I had originally hoped to have the new furnace routed into the old. Only one HVAC man would do that but then realized that would not work.

    So the old furnace will be kept but the asbestos pipes will be removed except for about 12 inches from the furnace to show how they looked. There will also be a deed restriction – easement to prevent future owners from removing the octopus.

    Being a purist, I feel very bad about not using my antique furnace, but doing it this way will assure that it will remain as a decoration in my basement for future generations to enjoy.

    Check out the picture – I think you will like it!

    kari dunn October 12, 2012 at 5:24 pm

    We, too, still have our gravity furnace intact. It was installed originally as a coal burning furnace, there is still some coal down there in the bin. Now gas, wonderful, quiet, dustfree heat. Yes, ineffecient, but not as bad as people say they are. My biggest complaint is how much room it takes up, but heck, it’s a 1000 square foot basement…how much basement do I need at this point? Thanks for the article, good to have as much info as possible when the time comes to set the octopus free!

    Ron Hart February 26, 2016 at 2:15 am

    I have been told no way to retrofit my home easily or without spending $40,000 for the ranch style end, and another $20,000 for the large triplex addition. So when the pipes froze due to tenant neglect the home became useless for us. If this is a way to add a lower cost heat-a/c combination. I’m definitely all ears. The only thing we can do to pay for this huge home renewal now, is to turn our home into a display home of new products and remodeling results. If any contractors or construction material manufactures could help, please contact 231-903-9738. There is more work than we could ever complete on our own withnthis home. Muskegon, MI 49442

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