Replacing old heating systems, starting from scratch


There's something to be said for a truly terrible old-house part: At least you don't have to agonize over whether to keep it.

That's often the case with old heating systems -- where they remain. The 120-year-old house we're working on has evidence of three types of heat, none of them much good.

The most recent was actually the worst. When the house was converted to apartments (sometime around World War II, we think), someone installed a scattering of gas-fired space heaters. Since the house had gas lights before it got electricity, the heaters were easy to install. But vents weren't that easy, so some of the heaters were vented to the outside, and some weren't.

Unvented space heaters are dangerous -- the fumes can cause illness, even death -- and unburned gas collecting in the house can ignite and blow the house to bits. In many places (Baltimore City included), unvented space heaters are illegal.

The next most recent heating system was probably the best, though the term is relative: a "gravity" hot-air system with a large round furnace in the basement and a few ducts running through the basement to first-floor vents, and even fewer channeled into the brickwork of the walls to higher rooms.

There were very few vents, so the heat was certainly uneven. A gravity furnace works because hot air rises. There was no circulating fan, so the air didn't rise very fast, though eventually it might deliver enough warmth for comfort. If a vent on the first floor was open, most of the heat would go there.

This kind of system, which usually burned coal (hand-fed in the basement) was probably installed around the turn of the century. The same old furnace was often later converted to burn oil, simply by cutting a hole in the chamber above the place where the coal used to burn and mounting an oil burner on the front of the unit. Most of the time the ductwork wasn't changed, so it was still an inefficient way to heat.

There are still a lot of converted coal-to-oil furnaces in Baltimore basements, though we haven't seen a coal-fired furnace for some time. (Randy thinks he saw one, burning wood and assorted useless items of furniture in East Baltimore about 10 years ago.)

Before the gravity furnace was installed, our house most likely was heated by fires in five or six fireplaces. The house has two chimneys in the front, with two unlined flues up to the roof, and one chimney in the back, also with two unlined flues to the roof.

It's likely that an early kitchen was in the basement, or ground-floor level. A stove and room heaters in upper levels were then vented into the flue.

There's no question of restoring the back fireplaces; the flue ran through a party wall on the third floor of a neighbor's house, and he (not surprisingly) removed it. Given enough time and money, we hope to reline the front flues for a working fireplace on the first floor and a wood stove on the third floor. (Modern building codes require a lined flue for each appliance, so one flue won't do for multiple stoves.)

As for the heating system, we're starting from scratch. The old furnace was long gone, and so was any early ductwork -- which wouldn't do for air conditioning anyway. Since the exterior walls are plaster over brick, there's no cavity to run new ductwork through.

We're going to install a new high-efficiency furnace in the basement for heat (check your local utility company; some are offering incentives to people who install super-efficient equipment) and a compressor outside for air conditioning.

Making the systems work, however, requires adequate ductwork. There are some simple (and immutable) principles involved:

*Every room needs at least one vent (register); some rooms need two or more.

*Each vent should have its own duct running from the basement. Two or more vents should not be "stacked" -- that is, fed on different levels by the same duct.

*Neither heat nor air conditioning will work well unless all of the cooled air (in the winter) and the heated air (in the summer) are returned to the main unit for reheating (in the winter) or for recooling (in the summer).

A heat-only system needs an air return at the lowest central point in the living space (for instance, on the first floor at the bottom of the stairs to upper floors) so the once-heated air that naturally falls as it cools gets channeled back to the furnace for reheating.

Air conditioning requires returns at the highest point of the house, so the once-cooled air that has risen as it heats can be collected to return to the main unit for recooling. More efficient cooling systems have returns on every floor; the most efficient would have a high return in every room for summer as well as a low return for winter, but that's not a practical goal for most rehabbers. It's just too disruptive to retrofit that much ductwork.

We firmly believe that the best heating and air-conditioning system for an old house is the one that's least visible. Here are some of the things we're doing to allow installing ductwork in the least disruptive way:

*Room layouts were planned to accommodate the exhaust vent from the furnace and cold-air returns, which are the biggest pieces in the duct system. For instance, two high returns (taking warm air back to be recooled) will fit neatly into the back of closets.

*The furnace was located below the front fireplace flues, so we can build extra space in "chases" (boxes enclosed in drywall) at the sides to run ducts to the upper three floors and vents to the roof.

*Vertical studs in stud walls should be aligned with floor joists so there is a continuous horizontal and then vertical "bay" to run a duct. (If the studs and joists don't line up, the ductwork will run into the bottom of the studs -- at least, until the heating contractor brings in the chain saw.)

*Any ductwork running through unheated spaces will be insulated.

*Most of the rooms will be rebuilt -- framed out to leave room for all the systems, plumbing, heating and air conditioning and electricity. There was not enough historical detail to save the walls. The rooms will still have the same proportions as the old, the historical details will be reproduced -- and the modern equipment will be almost invisible.

Next: Answers to readers' questions.

Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is a home writer for The Sun.

If you have questions, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.

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