Thursday, 28 February 2013

Heat Loss is Invisible - See Where it's Gone!

Heat Loss is Invisible - See Where it's Gone!

Richard Jessel's Calculation  GRAPH (pdf)   He calculated the figures below and used these to produce the  graph.
See common problems below this chart, with samples of different permutations which must contribute to the complexity of producing a universal document for heat and money loss for a letter box?? R's "had a go" for a simple guide.

So far there has been no success on our part to find specific documents concerning heat loss and money loss dissipated from a STAND ALONE letter box.  There may be some out there, and if anyone who reads this and can help we would really appreciate your contact.

Letter boxes as part of a door perhaps is a different story re documentation,  but it's a fact that the problems from this silent culptrit can still be applied.  

There are so many permutations when evaluating the loss of heat and the incoming of cold air through a letter box.
When the box is shut firmly and tightly,  this pretty well removes the problem.  
However,  how do you gauge and document the energy lost through a flapping letter plate, a rattling letter box, a broken letter plate, one missing all together and the various angles of opening sucombing to jamming by various thickness's of mail and small packages?

Broken spring - heat loss here

 This maybe a favourite!  but needs some protetion behind.

There's so many styles of letter boxes fitted into a door
The modern way  - lifting upwards. 
The traditional way - of pushing through the aperture,  horizontal or vertical and all coming with - or not -  brushes,  flaps, curtains.



Opening difficulties of the letter box can be taken into consideration too. Heavy springs seem to be the norm to keep it shut.  The post can hardly get through and when it does - if it does - is crunched due to more obstacles and often gets stuck.  Also another valid point - consider the extra time this takes tackling the delivery,  with the letter box open to the elements allowing your heat to escape and cold air to trickle in.
Even fingers.  This is certainly not nice mentioning this, but why not?  the fact remains it happens. There are many case histories on the web. To name just two blog spots....

Heat loss here

The above can be applied to your beautifully insulated door too - it really defeats the object unless you have an outside letter box - have to open the front door to retrieve your mail and papers.  More heat loss. Porches will help,  but actual posting difficulties are not completely alleviated and could apply to   through the wall letter boxes,

Added to all this 
We then come to the material of the letter flaps.  Are they metal? are they plastic? each having different thermal conduction characteristics - coming into the home or going out of the home.


Even the colour can either absorb or radiate heat.  All this together with the variable air temperatures outside your home and inside your home...and wind pressure and... not forgetting humidity. 

How can a stand alone letter box be universally gauged for heat,  energy and money loss? As mentioned,  if there are such documents please let us know.  

Meanwhile, the guide to heat loss costs above have been devised by Richard using some of these variable situations.  He has done the best he can at the moment.  
It gives an indication of the Thermal Units you need to replace the heat loss under these variable conditions (only you know what you pay per btu - and the way your letter box behaves.) 

Bear in mind...

Once you have warmed your home you will then only pay to replace the heat that you are losing by having inefficient thermal or draught protection.


You need 100 standard open keyholes to equal one letter box

There are many forums on the internet that have specific letter box threads with many suggestions of overcoming general difficulties with their letter box.  Just a few of them are mentioned above and... with some of the permutations.

How often is this ignored? - heat loss here

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