The secret to heating old churches

Published: June 9, 2015 - by Dan Holohan

Categories: History Lesson, Darn-Good Stories, Case Study

Liverpool Cathedral 7684921888

The Lovely Marianne and I attend Catholic mass at a lovely church that rose from fertile Long Island soil in 1924.

The parishioners did nearly all of the construction, which tells you something about both those days, and how people have changed. The roof of the church is laced with thick, brown beams, all in line and meant to resemble the upturned hull of a schooner, Long Island, being just that, and many of those parishioners being fishermen. It’s quite beautiful.

And it being 1924, the men who built the church chose to heat it with steam, which used to make me smile as I sat through homilies, listening to both our pastor and what sounded like Satan hammering away inside the pipes. You can’t fix faulty steam traps with prayer.

When 1995 arrived, contractors rather than parishioners showed up and expanded the old church, turning the inverted schooner into a cruciform and making room for more of the faithful. They tore out the old Warren Webster steam system and replaced it with a tiled, radiant floor. It was a nice change and it cut the parish’s fuel bills in half, even though the church now had nearly twice as much floor space as it had in 1924. This was possible because, with radiant heating, the air stays at a fairly constant temperature from floor to ceiling. There are few convective air currents in a radiantly heated building, and this is especially important in any building that’s as lofty as a church.

Liverpool, England, the birthplace of modern hydronic radiant heating, has a famous cathedral that looks as if it’s been there since King Arthur, but don’t be fooled. They built that gorgeous cathedral between 1920 and 1961, with an understandable hiatus for World War II. It, too, has a radiant floor, but hot air, not warm water, directed through buried channels, heats that stone floor, and it’s a fine place to consider the concept of convection. During the heating season, the air temperature four feet above the Liverpool Cathedral’s floor is 60° F., while the air temperature at the clerestory, 97 feet above the floor, is 58.5° F. A very slight difference indeed.

In 1897, Walter Jones, an Englishman, wrote a book for American contractors. He called it, simply, Hot Water Manual, and his purpose was to compare British and American ways of heating buildings at that time, and in the times preceding. He was a lover of hot-water heating and speaks not exactly enthusiastically about steam heat, which was strictly an American thing back then.

When it came to churches, on both sides of the ocean, he wrote, “One of the greatest difficulties is to prevent down draughts of currents of cold air, and this tendency exists in all lofty buildings, whether they are heated by high- or low-pressure hot water, by steam, or by hot air. The greater the difference between the inside and the outside air temperature, so, in proportion, will the tendency to down draughts be increased. The higher the temperature of the pipes or the hot air, the stronger will be the currents; hence the low-pressure system is the best, because a larger heating surface is presented at a milder or more humid temperature. You may frequently see persons looking up at the roof, ceiling, or windows to find where the draught comes from, when the cause is from a totally different source. If the pipes are intensely hot, the currents of heated air will ascend more rapidly, and displace in the same relative proportion the cooler air in the upper part of the building, and these currents are very objectionable.”

When Mr. Jones writes of low-pressure systems, he also means low-temperature. I thought back to our church’s old Warren Webster steam system. Those radiators were hot but each radiator had a box built around it. The old church was crowded and people often stood in the aisles. Those near the radiators put their coats on top of the boxes, but that’s not why those boxes were there. When you place a solid barrier such as a shelf or the top of a wooden box over the top of a radiator, you cut the radiator’s output by about 30% because you’re impeding the convective movement of air. This also means that the air won’t rise as high within the church as it would, had the boxes not been there.

Which brings me to the late-70’s.

OPEC got our attention in’73 with their first oil embargo. If you’re old like me you’ll remember how we got to know our neighbors better by fighting with them as they tried to cut into those long lines approaching gas stations.

And it wasn’t just the gasoline that got expensive; the price of heating oil and natural gas also soared. Churches, and other lofty houses of worship, were especially affected because the faithful put less money in the baskets during those tough times. So the clergy looked for solutions, and one of those solutions seemed to be the ceiling fan.

Actually, more than one ceiling fan. Someone told the clergy that heat rises, which it doesn’t. Hot air rises. There’s a difference. Consider that beautiful cathedral in Liverpool, England. Up near those high windows, 97 feet above the floor, the air temperature is only 1-1/2 degrees cooler than it is four feet above the floor. Air won’t rise unless you heat it, and a floor radiant system doesn’t heat the air; it only heats the people.

But the clergy didn’t know that during the late-‘70s, so lots of ceiling fans went into to those lofty buildings in an attempt to bring down the hot air. But when the clergy hit the switch, the fans began to take what was actually relatively cold air up near the ceiling and mix it into the relatively warm air that was down there with the people. That lowered the overall air temperature within the building, which caused the thermostat to keep the burner running. Naturally, the fuel bills increased.

This is why, if you are of the faithful, you will never see those fans running during the winter. You’ll see them on only during the summer.

And since I learned about this, I’ve heard from contractors who have had the opportunity to replace boilers in old churches. These folks are professionals, so if it’s a steam system, they go around and measure all the radiators and check out the piping for the proper pick-up factor. That’s the only proper way to size a replacement steam boiler. If it’s a hot-water job, they do an accurate heat-loss calculation on the building.

But then they call me because they learn that the boiler and radiation that have been in that old church for 100 years or so is too small to heat the building, even though it’s been heating the building for all that time. And to understand why this is, we have to hark back to Mr. Jones and other writers of heating text books back in 1890s when all of this was new. Contractors in those days took the advice of the book writers and sized the heating system to be relatively low temperature, and smaller than the actual heat loss of the building. They wanted to heat people without creating convective drafts within the building. They deliberately undersized the boiler and radiators, which leaves the modern contractor with some sphincter-puckering decisions to make.

But that’s the secret to heating old churches.