Thursday, September 22, 2011

Fireplace Door Report part 2


Experimental Fireplace Door
part 2

Measuring the Temperature of the Stonework just above the Door

After some time into using the fireplace door, it became obvious that it was drawing too much air from the underfloor inlet, and thus causing the fire to burn too brightly and without sufficient control. The problem; the Baxi air inlet control valve was only a very loose fitting butterfly "flap".

The answer to the problem required that the butterfly valve, in the Baxi underfloor unit, be modified, because, in its present form,  it was incapable of sufficient control of the now much higher pressure of air being drawn through the vent.

To do this I cut two "washers" from some thin silicone rubber sheet, and sandwiched these with a circular piece of aluminium to the back of the butterfly flap. This required a good bit of careful cutting and trimming, as the end result needed to be more or less airtight.


Silicone Rubber sheet and a circle of Aluminium to make an airtight valve
When I eventually got the valve to fit properly, I found it was very tight to turn and not at all easy to adjust. The answer to this problem, was to lubricate the affected part of the inside of the air supply tube along with the edges of the rubber washers with some silicone grease. Now the adjustment was smooth!!

Now, at long last,  I had an airtight (more or less) butterfly air intake valve. Which was capable of fairly precise control of the primary air supply and thereby gave me.precise control of the burn rate.

The Next Problem

Silicone Compound completely sealing around the edges

The next problem to present itself, was air leakage around the door frame. The only answer to this was to completely seal all around the door frame edges with some silicone filler.

The Gained Advantages

These above modifications gave me the degree of air control I needed in order to get a fully controlled burn. One fill of the fire with smokeless coal now will keep it burning now for 6+ hours, and it is even possible to get overnight burn.

Another major advantage was the noticable increase of heat transferred to the radiators via my County Kerry made "Firebird" high efficiency back boiler.

1.50m up the chimney 5hrs after the fire had gone out 28 deg C

Yet another advantage of the air tightness was the heat transferred to the fabric of the chimney breast.

Initially, I was a little worried that there might be too much heat accumulate in the brick and stonework. In fact a SEAI official stated to me in a phone conversation that this was a prime reason for their not promoting fireplace doors.

This worry however has proved so far not to be a problem. The heat does build up, over several hours, to about 40+ degrees, and it is retained for many hours after the fire has gone out. The chimney become a sort of storage heater!!

A bucket of coal now delivers me exceedingly good return in terms of heat output. I am most pleased with the experiment thus far.


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