Thursday, December 01, 2011

Tackling Chimney and Fireplace Heat Loss


Tackling Heat Loss 
from Open Fireplaces

Got this letter today, from Gavin Harkness, asking about how to deal with heat loss and draughts caused by an open fireplace chimney, and I think it is timely to deal with this subject here and now.

I've been following your blog for a couple of months now, as I try to get a handle on all the various Energy Efficiency technologies and how I can adapt them to the house that I'm renting.

Being from tropical Australia, heating wasn't really a problem, so it's been hard to get real answers about what works and what is available. I live in a very efficient, modern house, with an outdoor oil heater and an open fireplace (no back boiler). With it's underfloor heating and good insulation, the house is maintained at a constant 20C.

What has been irritating me is the open fireplace, sucking valuable warm air straight up the chimney. We only light the fire for mere aesthetics purposes. No one, including a couple of BER assessors could give me a solution. I've been reading your insert fireplace reviews, but I could (not) see myself paying €1000, nor my landlord (either). But today, I found (a website by) these guys (who offer a kind of chimney trapdoor that shuts off the flue when not in use - costing 250 Euro fitted). It would be interesting to hear your thoughts on these sorts of products. Gavin Harkness.

Chimneys act like HUGE Vacuum Cleaners 

Think of a chimney on an open fireplace as the hose of a GIANT VACUUM CLEANER. It is constantly sucking huge amounts of air out of the room. That is fine in summertime, but in the winter, it is sucking out the heat and causing draughts to come in under the doors and through every possible crack and cranny.

My preferred method of dealing with this problem is as I have already extensively outlined in previous posts to this blog - with fireplace doors or with inset stoves.

Gavin's problem is that he is in rented accommodation and does not want to invest big money in another persons house.

A Few Possible Solutions

The cheapest and simplest solutions would be:

(a) To stick something up the chimney when not in use. Problem is forgetting it was there and lighting a fire would create a bit of a disaster. If, additionally,  the chimney stopper was flammable that would compound the problem. A perhaps safer way of doing it would be a heavy duty balloon - which is mostly air - there are proprietary chimney blocking devices which are essentially blow-up plastic bags. All of these methods are messy, especially when you go to take the thing out of the chimney.

(b) SAFEER CHEAPER and SIMPLE - Make a temporary screen, ideally of metal for safety,  that fits fairly tightly into the fireplace opening. This will effectively block the air flow up the chimney, and it can simply and easily be removed when you want to light a fire.

More Permanent but FUSSY Solutions

There are a number of permanent fitted solutions on the market, but these are fussy at best and bloody expensive for what you get. Above pictured is a neat cast iron chimney throat damper. The damper itself is about €200 and then there is the cost of fitting. That is perhaps something akin to the idea  mentioned in Gavin's letter above.

Above is a drawing of a chimney top damper. This type of damper is operated by a chain from below. Again it can be costly enough and there remains the danger of forgetting to open it when lighting a fire.


As a temporary solution I would personally go with a fitted screen into the fireplace opening. A nice piece of aluminium sheet cut and basically formed to fit.

(1) Cost would not be more than about €20 to €40. You could even do it DIY if you are any way handy.

(2) You could NOT possibly forget to remove it when lighting a fire, and

(3) There would be no associated difficulties or dangers involved.

So Much for the SEAI and its spawn - BER Assessors

SEAI (Sustainable Energy Authority of Ireland) would never come up with simple and inexpensive answers to energy efficiency - neither evidently can their offspring the BER Assessors!!

So - Gavin have I answered your questions? About my fee  - - - - - -


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