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Losses Through Gas Fireplace Vent/Duct?

lance_p | Posted in Energy Efficiency and Durability on

Climate Zone 6A, Ottawa ON, building a highly insulated house.

Does anyone know what kind of losses you can expect from the envelope penetration for a gas fireplace?

I’m thinking about our new house build and looking into options for our family room. Being a man who likes working with my hands I love the idea of chopping wood and stoking a real fire, but that’s just not a reality for this build. It will either be a gas or electric “fireplace”. Oh, and I get it… let’s not debate the aesthetics of the different types. For me, 99% of the time it will be a black hole in the wall decoration piece. I can see us actually using it about 10 times per year, and mostly for the ambient effect.

We’re up in the air as to whether we will hook up to the NG service at the road; my wife wants NG just “because”, but I’d rather not have it.

With regards to fireplace cost, this is how I see it so far:

1. Gas fireplace is cheaper to run ($/Btu)
This is not a huge deal for me since we won’t be using the fireplace to heat the house, and we will only be using it on rare occasions (movie night, company, etc.).

2. Electric is cheaper to buy and install
All said an done, a gas fireplace could cost up to $10k. An electric could be a fraction of that, especially a thin modern looking unit that can hang on a wall.

3. Gas requires a sizable envelope penetration of questionable air-tightness/insulation
This is the one I’m not sure about. Yes, while it’s operating the gas unit will have a higher Btu/$, but when it’s not working it’s a potentially leaky hole in the wall.

I would like to be able to justify against the gas unit based on the cost of energy losses alone. Anybody care to throw some estimates out there? When it’s sub-zero Fahrenheit outside, how much does a gas fireplace really cost on an on-going basis?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Lance,
    If I understand you correctly -- you will use this fireplace 10 times a year, in all cases for ambiance, not heat -- you should buy the electric model.

    If possible, avoid hooking up to the natural gas pipeline (to avoid the monthly utility charges that you will incur even when you don't use any gas).

  2. FourForHome | | #2

    I installed a propane FP for ambiance and emergency heat in my 1.25 ACH house. The FP turns down to about 4k btu/hr (so I can actually use it) and has lights inside so it can look pretty all the time. The propane usage costs less than the monthly service fee for NG.
    I haven't measured whether there is an energy penalty vs having no FP.

  3. STEPHEN SHEEHY | | #3

    If you only plan to use it once in a while, you might want to look into an alcohol fireplace. Installation is simple, fuel is available, probably cheaper than either electric or propane.

  4. user-5946022 | | #4

    Stephen's response to consider an "alcohol" fireplace is interesting. I had never heard of such, but googled and came up with Ethanol Fireplaces.

    Apparently these Ethanol Fireplaces are "vent free." As such, are they safe? Does anyone make a vented one?

    Would this be a reasonable alternative to a direct vent gas fireplace in a very tight house? Seems like it would be able to provide ambiance better than a direct vent gas, because the direct vent gas fireplaces all have enormous btu's, so you can run them only a short time in a tight, well insulated house. Would the ethanol fireplace be something you could run longer for ambiance?
    Would it also give out some heat, so it could be considered a backup heat source in a power outage, especially for a tight house?

  5. lance_p | | #5

    Martin, correct, it will be mainly an ambiance appliance, and avoiding the $25/month utility service fee is a very attractive benefit.

    Mark, my plan was to use propane to heat our hot water year round. As you pointed out, the fuel cost would be a fraction of what just the service fees are on a gas connection, and it could be used as a source of emergency heat if we ever had issues with our air source heat pump (primary heat source).

  6. lance_p | | #6

    Stephen, that alcohol fireplace looks like an extremely attractive option! Not only is it a real fire, but it actually puts out some usable heat as well. They are also much thinner than typical gas fireplaces which may free up enough space to put a closet behind it (we have a hallway behind the fireplace wall in our floor plan).

    C L, I looked into the pros/cons of these alcohol fireplaces and, according to what I've read anyway, the only byproducts of combustion are heat, water vapor and carbon dioxide. They don't recommend using these fireplaces in small poorly ventilated rooms, but in our open concept design that wouldn't be an issue.

    I'm also thinking I could place an exhaust port for our mechanical ventilation nearby that could be opened only when the fireplace is being used. That way the CO2 and moisture from the unit would be extracted at the point of use.

    I found a local (Montreal) company that makes these fireplaces, and some of their products are sold through Home Depot in the US. They have a nice FAQ page for anyone who's interested:

    https://www.eco-feu.com/about-us/

    I contacted the company and asked about the heat output control on the variable models, since only the maximum Btu is listed. They claim that, depending on the unit, the minimum output can be from about 60% down to about 50% of the maximum output. The "Montreal" looks to be a nice size for our application as it goes from 4000-6500 Btu. The larger model I originally asked about, the Santa Cruz, varies between 9000-18000 Btu, way too much for our family room.

    Having said all that, I don't think it would be a good source of heat during a power outage. You would need mechanical ventilation while using it as it consumes oxygen and produces CO2.

  7. user-4053553 | | #7

    Vent free means it uses your room as the chimney. All the combustion products will remain indoors for you and other occupants to breathe in. They are a terrible product but are legal because of lobbying and judicious use of corporate government influence.
    There is a GBA article on this but i can't find it in the search

  8. user-5946022 | | #8

    Here is a link to an older GBA discussion:
    https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/18230/bio-ethanol-fireplaces

    And here is the direct link to the article referenced in that discussion:
    https://www.sciencedaily.com/releases/2014/09/140903091728.htm

    Without knowing anything about them, they sounded like a poor idea. Apparently science confirms that. They might be ok if they were direct vented like direct vent gas fireplaces, but I don't see any such options.

  9. lance_p | | #9

    So the report in Science Daily references a study done by the Fraunhofer WKI. The study is referenced here (caution, LARGE pdf file!):

    https://www.wki.fraunhofer.de/content/dam/wki/de/documents/Mediathek/jahresberichte/WKI_2013_double-page.pdf

    Note, it is promoted by IKEA. I'm not sure if that's relevant or not, but it seems curious that a private company would be behind the study? Fraunhofer WKI is a wood products application research facility. Could there be politics involved here? Seems a little far-fetched, but why would IKEA not sponsor more seemingly relevant research like bonding of wood laminates, etc.? Just tossing that out there, I'm no expert in the wood industry.

    The emissions test chamber used was 48 m3 in volume, about equivalent to a 200 sqft room. They claim to have "ventilated the test chamber according to manufacturer instructions". I'm not sure how that's possible since the whole premise of a test chamber is to perform a test in an isolated environment? Also, after reading the installation instructions for one of Eco-Feu's fireplace units, there are no detailed ventilation instructions, only recommendations to not use their products in small rooms for long periods of time with the doors closed.

    Without studying the details of how this test was conducted, I'm willing to say that we don't have nearly enough information to conclude the validity of the claims put forth. Examples:

    1. How long was each test run? In an otherwise sealed environment you would expect the concentration of pollutants to rise with time. The DIN 4734-1 standard was referenced as a source of information for impact to air quality, but not the test method.

    2. What is the air change rate of the typical indoor room where such a device would be used, and what is the total volume of the typical house with which it shares its air? This would be important to duplicate a real life scenario.

    3. Fireplaces were also tested, but they were tested in people's homes. Why were the fluless ethanol appliances tested in a chamber instead of in people's homes, like the real fireplaces were?

    4. Which fuels were used? The article mentions both liquid and gelatinous fuels. I'm assuming there are additives (impurities) in the gelatinous fuels to make them gelatinous compared to the liquid fuels?

    5. Which fuels were used? The study mentions the test results will be swayed by fuel type, quality and incineration temperature, but doesn't mention the particular fuels they chose for the test.

    6. Which appliances were used? The quality of the incineration may be dependent on the design/quality of the appliance.

    7. Incomplete data. The article only mentions the worst case scenario for each test point and doesn't relate it to a particular type of fuel or appliance.

    8. The opening paragraph focuses first on the safety of these appliances and reads almost like fear mongering, which is followed by the statement that ethanol fireplaces increase indoor pollutants. Later they suggest there's a real concern that "the entire room could go up in flames." This article reads more like Fox News than a science paper.

    I sent an email to Eco Feu referencing that article and asking their point of view. They claim the quality of fuels available has increased substantially in recent years. They also claim that every one of their fuels and appliances have passed UL and ULC testing standards for use both indoors and outdoors (as far as I can tell, they only sell a liquid bio ethanol fuel.) They also suggest that many of the products on the market may not be tested to those standards, which coincides with points made in a few other articles I read.

    I'm not trying to argue that these ethanol burning appliances don't decrease indoor air quality, I'm merely trying to look at the claims of that article from an objective point of view. I work in a standards lab, and our facility includes all sorts of testing facilities for physical and chemical properties. I find it hard to read ANY report without questioning the methods used and feel I'm always better served by questioning things rather than just "taking someone's word for it".

    It would be interesting to see how these test results compare with common bad practices like burning a candle, using a gas stove, or tossing a fabric softener sheet in the dryer with a load of laundry. My Spidey senses tell me that there's probably not much to worry about in most cases. I'd love to be able to prove whether I'm right or wrong...

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