by Dan Holohan, Dan Holohan Associates
by Dan Holohan, Dan Holohan Associates
Old cast-iron radiators, very often in Victorian splendor, stand guard over the chills of winter, and many homeowners hate to part with these beauties. Other homes have heating systems that literally disappear beneath the surfaces of the rooms as radiant panels. Just about anything is (and always has been) possible with hydronics.
Older cast-iron radiators, the sort used on "one-pipe" steam heat, have nipples only across the bottom portion of the individual radiator sections because steam is lighter than air. When the steam enters the bottom of a radiator it flows upward into the radiator sections, pushing the air from a vent.
Hot-water radiators, on the other hand, have nipples across both the upper and lower portion of the radiator sections. Even though hot water rises, it doesn't move as quickly as steam. The double set of nipples encourages better circulation of the hot water through the radiator.
Around 1905, when "two-pipe" steam became popular, contractors began to use hot-water radiators on their steam systems as well, and those old steam radiators with their single set of bottom nipples soon became obsolete. Several manufacturers continue to make freestanding cast-iron radiators with the upper and lower push nipples, however.
If it's an old radiator you're looking for, you can take potluck at your local junkyard, or you can call Fran Fahey at A-1 New and Used Plumbing & Heating Supplies. Fran operates a veritable supermarket of antique radiators in all shapes, styles and sizes, and he has repaired and pressure-tested every one of them. He'll ship anywhere in the country, and he'll also fix old radiators that have push -- not threaded -- nipples connecting the sections.
There are also brand-new, cast-iron radiators available that
look old (and gorgeous!). Low Energy Systems offers these Victorian-era
beauties that whisper nostalgia and romance through delicate scrollwork.
They're perfect for period homes.
Burnham Corp. makes a radiant,
cast-iron radiator that you can recess into the wall. These are
very popular as replacements for old radiators in parts of the
country such as New England and Long Island where there are many
older homes. One of the neat things about cast iron is that it
holds its heat for a long time, and freestanding radiators (even
when recessed) give off about 40% of their heat as a radiant glow
(the rest of the heat moves by convection). They're very nice
to be near.
Similar to these, but made of steel, are the European-style panel radiators available from Buderus. You can recess these flat-panel beauties into a wall as well and enjoy that radiant glow all winter long. You can also paint or paper these units, making them nearly invisible. The only thing you'll notice is the comfort.
Beyond free-standing and recessed there is a world of radiation known as "towel bars." They're modern, pleasing to the eye, and available in a wide range of shapes, sizes and colors. The do a marvelous job of warming the bath (as well as that terry cloth!). A great source for this type of radiation is Low Energy Systems in Colorado.
If you want the radiators to disappear completely from sight,
then a radiant heating system is what you're after. In an older
home, you can install these systems by attaching the radiant tubing
(which is made from either plastic or rubber) directly beneath
the floor. This process (called "staple-up") is like
lacing a sneaker. You start by drilling a series of holes through
the joists and then lacing the tubing up and down the joist bays.
You can attach the tubing beneath wood floors, tiled floors, and
even floors with rugs, but success depends on the sizing of the
system. Work only with someone who has had experience with radiant
if you're considering this method. And here are a few things
you should watch out for when you're thinking radiant:
Three walls of glass. The heat loss in a room with three walls
of glass will be about 20% more than it will be in an identical
room with just two walls of glass. Keep in mind that you have
just so much floor space available to act as the radiator. You
can only release about 35 BTUH per square foot of floor space.
If you exceed that "rule of thumb" limit, the homeowners
are going to have hot feet. Also, you can damage wood floors if
you let the surface temperature exceed 85 degrees Fahrenheit (which
it can, if you're pushing more than 35 BTUH/square foot). If there's
not enough floor space, don't despair. You can put radiant tubing
in the ceiling or the lower walls.
Prevailing winds over 15 mph. The house you're dealing
with might be in a place where the wind blows all the time, and
if it is, be careful. Wind can weasel its way into cracks in the
house and create drafts. If the house is near the ocean or up
on top of a hill, take note and figure that into your radiant-heat-loss
calculation. A radiant-heat-loss calculation will always be less
than a convective-heat-loss calculation (the latter being the
traditional method) because a radiant-heat-loss calculation pretty
much ignores heat loss by infiltration. It can do this because
a radiant heating system makes the air inside the house very still.
Still air is less likely to promote infiltration because there
are no convective air currents moving past the windows and doors.
When the wind is howling, however, this can change, and you'll
have to compensate when you're figuring the heat loss. If you
don't know how to do a radiant-heat-loss calculation, get help.
Rooms with lots of stone. People who camp in the woods on cold nights have a trick that helps them keep warm. They'll put a couple of big stones in the campfire and when they're ready to turn in for the night they'll take the stones from the fire and lay them inside the tent. The stones slowly release their heat inside the tent, and if the camper keeps the flaps closed, those stones will keep the inside of the tent toasty until dawn. Rocks hold heat, and that's why you should be careful with your control strategy when you're working with a room that has brick or stone walls, or a big fireplace. These rooms will take a bit longer to heat, and they'll stay warmer long after the water stops flowing through the tubing. "Stone rooms " work best when they're on their own zone.
High-hat lights. Because the standard ones have no insulation, high-hat lights can suck heat out of a room and stick it into a ventilated attic. They can add considerably to a room's heat loss. Several manufacturers make insulated high-hats that cost just a bit more than the standard type but create less heat loss. They can make a difference in a radiantly heated home.
Old houses. Assume the worst and figure on there not
being much insulation in the walls when you do your radiant-heat-loss
calculation. If possible, talk the homeowners into insulating
the place before they spend all that money on a heating system.
Wet wood. There shouldn't be more than 6% moisture in any
wood you're going to heat. If you staple radiant tubing under
wet wood, you're going to get a nasty surprise when the finished
floor dries and turns into corduroy. A moisture detector (available
in most tool catalogues) will show you the wood's moisture content
instantly.
Thick carpet. Putting a carpet and pad on a radiantly heated floor is like putting a sweater and winter coat on your body. Both keep the heat from escaping. If there are to be rugs, you should know about them. Allow for the higher R-value of the carpet and pad when you're doing your load calculations. I looked at a gorgeous house in Monterey a while ago. The place had hydronic radiant heat and carpets that were as thick as the owner's wallet. He told me that he warned the contractor he was going to do this. The contractor listened, and sized the system for extra tubing and a hotter-than-usual water temperature. As I write these words, that homeowner has been wonderfully comfortable for 11 years. Like I said, just about anything's possible with hydronics -- but first you have to know what you're up against.
Different types of heaters. I once helped a contractor troubleshoot a strange situation. He had put a kick-space heater under a kitchen cabinet. In the same room, but on the opposite wall, he had installed a recessed convector in front of a sliding glass door. He took great pains to size these heaters properly. He knew that on the coldest day of the year, the homeowners would need them both. But when the coldest day of the year arrived, the homeowners were cold in their new kitchen. They called the contractor and he called me. The only thing I could figure was that those two types of heaters weren't getting along. The recessed convector wanted the air at the floor level to be cold so that it could grab it, heat it, and send it up toward the ceiling. The kick-space heater, however, kept heating the air near the floor and sending it spinning toward the recessed convector. The heated air was interfering with the cold air that the recessed convector needed. The result was the recessed convector did very little heating. Water flowed through it, sure, but the water's temperature didn't drop by much because the heat wasn't transferring to the already warmed air! Some hydronic heaters, you see, don't play well with others. Keep that in mind if you put any sort of blower (or ceiling fan) that creates convective currents into a radiantly heated room. You just might mess things up on that coldest day of the year.
Anything's possible with hydronics -- both old and new. The radiators can be stately and out in the open -- or totally unseen. The only limit is your imagination!
Dan Holohan's books include The Lost Art of Steam Heating,
Hydronic Radiant Heating: A Practical Guide for the Non-engineer
Installer, and Screwing Up: 666 Ways to Go Wrong on Your
Next Heating Job. He also maintains a website, at http://www.danholohan.com,
with excerpts from his books and columns, and plenty of anecdotal
material on the science of hot water heating. His books can be
ordered online or through his company, Dan Holohan Associates,
Inc.,
Tel: 800-853-8882.