V.7.3
HYPOCAUSTS
TWO TRADITIONAL ROMAN TYPES:
CHANNELED AND PILLARED
Since the history of the Roman hypocaust has been fully
documented elsewhere, we may confine ourselves here to
the most summary review.[260]
This heating system, developed
to perfection by the Romans, is found not only in their
baths but also in practically every Roman villa north of the
Alps. The Roman hypocaust was either of the channeled
or the pillared type.[261]
In the latter, a good example of which,
from the Roman camp Saalburg, is shown in fig. 379, the
floor of the room to be heated was raised by short columns,
usually two feet high, a shallow chamber thus being formed
below the floor level. The heat, generated in a furnace that
was built against one of the outer walls and serviced from
the outside, was dispersed into this chamber and rose from
there in vertical flues imbedded in the walls. In the other
type, hot air was taken from the furnace through a trench
beneath the floor to the center of the room and then diverted
radially to the four corners into a channel running all the
way around the room, at the bottom of the walls, from which
point it rose into the wall flues, as in the hypocaust from a
building in block II of the Romano-British city of Silchester
(fig. 380).[262]
THE CHANNELED HYPOCAUST OF THE
MONKS' DORMITORY
On the Plan of St. Gall only those parts of the hypocaust
are shown which lie outside the warming rooms, namely
the furnaces and the chimneys (fig. 381). We are told
nothing about the layout of the ducts and flues that distributed
the heat in the rooms themselves. To do this in the
calefactory of the monks would have been impossible, as it
would have obscured the layout of the beds in the Monk's
Dormitory, which the drafter of the Plan considered to be
of greater importance. But in the warming rooms of the
Novitiate and the Infirmary, with no story above, he could
have gone into detail. Since he chose not to do this, it then
becomes clear that in his day the construction of a hypocaust
was a matter of common knowledge, one that required
no further instruction.
The furnaces are designated by the words fornax
(cloister walk in front of the Monks' Calefactory), caminus
ad calefaciendū (firing chamber of Monks' Calefactory),
and camin' (Novitiate); the smoke flues, by euaporatio fumi
(Monks' Calefactory) and exitus fumi (Novitiate). There
is no reason to assume that the furnaces were meant to lie
directly beneath the floor of the rooms they heated.
Nowhere else on the Plan has the architect designated
anything at the side of a building which was meant
to be beneath it. External firing chambers, moreover, were
traditional. Nor can there be any doubt about the location
of the smoke flues. They are meant to be where they are
shown: at a considerable distance from the outer walls of
the buildings they served, in order to keep the smoke away
from the windows of the dormitories and to reduce the
danger of their roofs being ignited by glowing cinders.
The hypocaust is superior as a heating system to the
hearth or the corner fireplace when large rooms and many
people are involved, since it is capable of distributing the
heat evenly throughout the width and length of the building.
On the Plan of St. Gall this heating system was provided
for the rooms that served as general work and reading
areas for the monks, the novices, and the sick.[263]
Since in the Carolingian cloister, the dormitory was
usually above a room warmed in this manner, the heat
could be transmitted to it through openings in the ceiling
or through wall flues.
As I do not know of any evidence for the existence in
the Middle Ages of pillared hypocausts, I am inclined to
assume that the hypocausts of the Plan of St. Gall belonged
to the channeled type. The Carolingian hypocaust of the
monastery of Reichenau, at any rate, belonged to this type,
and this holds true also of the tenth-century hypocaust
unearthed by Seebach at Pfalz Werla (fig. 209A-C).[264]
