"D. B. C," Dubois, Pa., writes: " I have built a new greenhouse which I want to heat by flue. Would you be kind enough to inform me what sized grate to use, and also the size of drain pipe for a house 20x50? Is there any way to clean those flues besides brushing them out ? Is there any chemical process for cleaning them ? The flue I have in use now is only to heat a small house, and I find it very difficult to keep clean".

[Eighteen or twenty inch bars ought to be enough for a grate for such a house. Ordinary drain pipe is vitrified or glazed. We have not found these as good as the unglazed ones, and we find those made of fire clay superior. For your house one with a six-inch bore would do but for the soot from bituminous coal choking it so soon. Eight inches would be better.

There is no chemical that we know of to clean these flues. In our case we had a moveable collar made for a number of sections. In this way a section here and there can be wholly taken out, and the rest easily cleaned. These collars must have a piece of wire fastened around them, or they will break when being filled with mortar, clay, or whatever may be used to close the joints. Wire should also be put around each piece of pipe to guard against the escape of gas should any one crack. The writer has had such pipes in a house for twenty years without renewing a single section, and working entirely to satisfaction. - Ed. G. M].