Here's a copy of the email I just sent to Ms. Marianne Armstrong concerning the report she and John Burrows authored entitled:
Impact of a Natural Gas Fireplace on Home Heating Energy Consumption
Ms. Armstrong is a research council officer in the Building Envelope and Structure program of the Canadian Centre for Housing Technology, jointly operated by the National Research Council, Natural Resources Canada, and Canada Mortgage and Housing Corporation (everbody got that? It will be on the final :-). Mr. Burrows is an engineer and technical writer.
I believe the report came up with a number of (to me) non-intuitive findings, but I'm not one to argue with science. I encourage everyone to read at least the summary, and I trust we can engage in some spirited discussion.
Of course, I can not discount the possibility that I am the only one who finds the report in any way surprising. We'll see...
As a retired EE in Carson City NV, I occasionally find spare time on my hands (usually between naps :-) and today spent several hours searching for information on optimal operation of my Heatilator, direct vent gas fireplace (25,000 BTU/h, input). You can imagine how pleased I was when I came across your recent report:
(I have hyperlinked [or copy/paste, as it turns out :-] the documents for members of Home Energy Pros, where I will publish this email: http://homeenergypros.lbl.gov/ ).
After reading the report summary, I was surprised to learn that, within the three sets of conditions under which you tested gas fireplaces, they actually had a negative effect on overall energy usage. Another surprise was that efficiency of the gas fireplace you tested was essentially the same, whether the fireplace fan was operated or not. I was pleased to hear the last part, since my fan is rather annoying (just need to confirm I have a similar unit).
I have been operating my unit essentially as described in your Scenario 3 (gas fireplace on thermostat), and since I observed substantially reduced operation of my 90% AFUE condensing furnace, I thought I was running my heating system in the most energy efficient fashion. Based upon your results, however, it seems the increased fuel input to a 76% efficient gas fireplace quickly offsets savings from not running the furnace. I believe I convinced myself that cooler temps in the "not fireplace heated areas" translated into lower fuel consumption overall. Again, per your report, that is not the case. Also, I may have been misled by high efficiency numbers I have seen for direct vent gas fireplaces (90%) vs your much lower measured efficiency in an actual installation (76%). In fact, I noticed today on the Heatilator website that they say their published efficiency only applies in a controlled environment, but I didn't think much of that statement till I read your report.
If only I had the luxury of side by side, identical houses, like you had for your study. I would have known these things years ago!
Lots of surprising (to me, anyway) information to think and talk about. Let's see if the folks at Home Energy Pro rise to the bait :-).
Steve Waclo EE, ret'd