of Ventilating and Warming Buildings. 265 
Isesides the disagreeableness of dusty rooms, it is not desirable 
to inhale air charged with particles of brick and mortar. When 
the matter of the stove is of sufficient thickness to limit the tem- 
perature to the proposed degree, it is not economical to make it 
thicker, unless the fire be kept on only a certain time, and then 
the damper and the ash-pit both shut close, so that no air can 
pass through the flues : then a considerable mass of materials 
will afford a regular supply of heat for a long time after the fire 
is out ; and you have to wait nearly as long a time before the 
stove affords any heat, if it be suffered to remain till it be cold. 
In fact, it requires a regular and systematic attention to manage 
such a stove, which renders it unfit for our uncertain climate, 
where the weather would very often change before the stove 
could be I'endered capable of affording its warmth. Consequent- 
ly, it is an obvious advantage to have the parts of the stove no 
thicker than is required to limit the temperature of its surface, 
because it then affoi'ds its heat speedily, and no attention to 
closing valves or dampers is necessary ; and yet the mass of 
heated matter round the fire-place is considerable, and therefore 
it is not very soon cooled, if the fire be neglected. As the length 
of horizontal flue is limited, and it is not convenient to make any 
material change in the size of ethe flues, the power of . the stove 
is usually regulated 'by the size of the fire-place ; but it is better 
to do it by the area of the aperture into the chimney; for then 
we can have a slow fire, which will require less attention. By a 
quick fire, we gain most heat from a given quantity of fuel, but 
it requires constant attention ; hence, where labour is more va- 
luable than coal, a slow fire should be preferred. The area of 
the aperture into the chimney may be determined by the rule 
10 c 
a. Where c is a number of pounds of Coal to be con- 
sumed in an hour, h the vertical height of the chimney in feet, 
and a the area of the aperture in inches, and if the quantity 
of air to be warmed per minute, in cubic feet, be multiplied by 
0-00472, the results ^inll be the pounds of coal which the stove 
to warm it should consume in an hour. 
Where a greater quantity of fuel than 10 lb. of coal per~;hour 
is required to sustain the temperature, it will be necessary to 
have two stoves ; as this is better than increasing the surface of 
the flues. 
