Hello All:
 
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...

 
Ms. Armstrong:
 
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 :-).
 
Be Well
 
Steve Waclo EE, ret'd
 
 
 

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Hmmm, two years in and no comments :-(.
Hi Steve, I can at least give you a comment :).
I read the summary and saw nothing surprising. The good news would be any reduction in efficiency is minor and the unit can function to some degree without power. I always advise home owners to pay attention to water pipes that are closer to the cold than any single source of heat when the power is out.

You mentioned an expected savings from using the fireplace with a much reduced cycling frequency of your primary furnace. In the test they performed they ran the main blower to circulate the heat from the fireplace as much as possible, This would defeat the benefits of an the overall reduction in house temperature you suggest. If you don't mind the rest of the house getting cold, leave the furnace blower off and just enjoy the fireplace. If the exterior heat transfer surfaces average just 5° less than normal you could expect a 15% to 20% reduction in energy consumption. That is based upon the reduction in HDD (heating degree days) due to a 5° lower base temperature. Of course you would probably not run 24/7 in that mode so the actual savings would be less as you revert to the primary system, and take your coat off :).

NOW, if saving energy is your objective, there are often some very easy ways to get started and I'll try to make sure it doesn't take 2 years to get an answer.

Bud
Bud,

I thought there was someone at the bottom of the well I was shouting into! Thanks for your comments.

As noted in the original post, my biggest surprise from the study was:

"The fireplace efficiency testing showed that the operation of the circulation fan built into the fireplace did not affect steady-state efficiency – this model of fireplace showed the same efficiency with and without the circulation fan operating."

Whodathunkit?

Now that my wife is also retired, she spends many contented evenings next to the gas fireplace in the recliner, cat and book in lap (cat usually under book :-), and Chardonay on the side table. To no avail, tried to convince her of the inefficiency of the fireplace and had no answer for her reply : "I worked hard for forty years to get into this chair and I'll be d#%ed if I'm not going to enjoy it!". If Mama ain't happy, etc. As I reported on another site, I cranked back the gas valve about 50% when she wasn't watching and no complaints so far :-).

Also, since she's home nearly all the time now, my "65F and a sweater" no longer cuts it. We have negotiated a settlement at 71F (with occasional fireplace operation as noted; the distant thermostat cycling moves heat from the great room, home to the fireplace). Northern Nevada has been in temperature inversion for a month with single digit lows and highs in the 30's. All told, our latest gas bill was an all time high for the ten years we've been here, but with all my improvements (closed crawl space, additional attic insulation, low level return added) we are still lower than neighbors I've spoken with (similar homes, etc.).

Also, you may wish to avoid engaging in conversation with me. As a retired guy with way too much much time on my hands, I can seriously eat into your time...I'll understand :-).

Best wishes
Well I guess the forum is in trouble as I'm a retired energy auditor. Actually I'm still trying to keep my hand in as I really enjoy this field. Being formerly from the engineering world I'm shaking things up a bit by asking questions. They usually just ignore me and do as they have always done, but I've made a few changes.
As for no improvement in efficiency when the blower is used I can only take a guess. Heat is delivered from an enclosed fireplace by radiation. Running the fan will lower the temperature (the heat has to come from somewhere) inside the glass, thus reducing the radiant transfer. The efficiency remains the same, jut the transfer method changes. Just a guess.
I certainly know the importance of keeping mama happy. I have often joked that all energy audits should include new granite counter tops or similar desirable improvements.
Now, with all of that extra time, if you are interested we can go over your heat loss and see if there are some good investments to be had. I'm plugging away at converting my small cape to a super insulated home so our $4 a gallon fuel oil doesn't eat up out retirement. I'm over half done and the comfort level has improved significantly. Mama said so.
There are some on-line heat loss calculators for the curious and I think the solar industry is approaching a cost level where it might be worth trying a small installation to get the bugs worked out. Of course my electrical costs make it a better option than yours, currently around $0.18 per KWH.

Glad to help. If I missed something ask again.
Bud
Hello Bud,

Wonder if we should go PM with further discussions?

Regarding your theory on fireplace efficiency, I believe you may have a good point. Considering fireplace total output as a pie, one large segment is radiant, and without fan operation, predominates. "Fan on" results in a lower temperature "fire surround", and radiant heat is reduced as btu's are captured by the moving air stream. Total pie however, stays the same (except for 25 watts of additional heat from the tiny blower motor :-). Makes sense.

I was on a construction crew a few years back and we were trashing polished aluminum reflectors from fluorescent lighting fixtures. I took one home, made a few modifications and put it behind the "logs" in my fireplace. By your reasoning, I simply made the radiant slice of the heat pie smaller while not appreciably effecting total output. Was still using the fan back then but as I recall, there was a notable increase in radiant heat from the unit, no doubt at the expense of heated air. Worked fine till the aluminum slipped into the flames and was damaged. That same construction site was where I got the hundreds of square feet of R-19 that currently reside atop the blown-in insulation in our attic.

At the risk of sounding smug, I believe I've gone about as far as I can go weatherizing our home. A blower door test several years back yielded impressive numbers (details escape me) and short of shoveling in more attic insulation, I don't see economical options available.

Your thoughts about PV are intriguing, but at about $0.11/kWh at the margin, ROI would not be attractive.

Took a two day course on solar hot water a few months back, but after the cost of engineering the roof-top mount, permits and hardware, was looking at $9000 (!). Our DHW use is minimal, but was considering using the system to drive a heating coil in my closed crawl space. Storage was going to be via a 2'X6'X10' reinforced canvas storage tank, appropriated from fire service applications. That didn't pencil either.

Tell me what you've been doing with the cape cod.

Best wishes.

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