Gas Fireplace suggestions for tight house
Last Post 03 Jul 2016 07:10 PM by Nashvegas. 16 Replies.
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peteinnyUser is Offline
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18 Aug 2011 03:58 PM
Who makes the most energy efficient Gas fireplaces? Do they have units that don't backdraft and use outside fresh air?
Lee DodgeUser is Offline
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24 Aug 2011 04:32 PM
peteinny-

There are commercially available natural-gas and propane fueled fireplaces that have sealed vented combustion systems. These draw outside air in for combustion air, mix it with the gas, and exhaust the burned gas products. These have no direct interaction with indoor air, so no backdrafting, but do provide heat to the room.

I have a Lennox MPD3035 that has a sealed combustion system, but it is not particularly efficient with an AFUE rating of 62%, meaning that, on average, 62% of the fuel energy is delivered to the room as heat. This compares poorly with my natural gas furnace that has an efficiency rating of 97.5%. I notice that Oregon has rating for gas fireplaces, with Tier 1 ratings from 65% to 69.9%, and Tier 2 ratings at 70.0+%, so I assume that there are models in that range.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
jonrUser is Offline
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24 Aug 2011 05:34 PM
So let's say a nat gas fireplace turned down low produces 20K btu/hr. So about $.11/hr net after accounting for the heat. Say 3 hours every day or $10/month. I like seeing a fire that much.





Lee DodgeUser is Offline
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24 Aug 2011 06:03 PM
Yes jonr, I meant to add in my previous post that although my natural gas furnace is efficient, it is not much fun to watch operate! I figure that compared to my furnace, my 20,000 btu/hr natural gas fireplace wastes $0.05/hr in heat going up the exhaust, so pretty cheap ambience. That conclusion applies as long as you don't have to run the air conditioner to offset the heat coming from the fireplace, like one of our former presidents used to do.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
peteinnyUser is Offline
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24 Aug 2011 06:31 PM
Thanks for the info on the fireplaces. I did not realize how inefficient they are. At only 60 percent or so that is not good. I guess it is more for ambience. With the whole tight house idea I would assume with no backdrafting that is a plus.
Lee DodgeUser is Offline
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24 Aug 2011 06:52 PM
peteinny-
Yes, when a house is tight, it is more important to use sealed combustion systems for fireplaces, furnaces, and hot water heaters.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
jonrUser is Offline
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24 Aug 2011 06:55 PM
I agree with Lee - no fireplace use with the AC on. I suppose an interesting question is why can't a "fireplace" be made as efficient as a furnace?
Lee DodgeUser is Offline
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25 Aug 2011 09:27 PM
jonr-

I think that it would be straightforward to improve the efficiency of the fireplace. Make the combustion volume smaller, increase the volume around the firebox and add heater exchangers around the outside to get the heat out of the firebox, and add a fan to get the heated air from the heat exhanger area to the room. But then you're just reinventing a furnace.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
SammyJoUser is Offline
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01 Apr 2013 10:22 AM
Have you thought of using a pellet heater? These little guys use bio-fuels to heat your home, and if you have a small home, you can turn the thermostat down and use it as the main heating source. It saves you money, and is more energy efficient than a regular wood or gas fireplace
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RGatesUser is Offline
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26 Aug 2015 11:00 PM
Lee, that product already exists, it used to be referred to as a heatilator. It was a metal insert that you constructed your masonry fireplace around . It provided a chamber around the fire box. Air was pulled from off of the floor circulated ,by means of fans, through the chamber and came out above the fireplace. It worked well.

Ron
Lee DodgeUser is Offline
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27 Aug 2015 12:15 PM
Ron-

The AFUE (annual fuel utilization efficiency) for some Heatilators ranges from 48% to 56% (http://hearthnhome.com/downloads/brochures/novus.pdf). Another model they advertise is AFUE rated at 69% (http://www.woodheat.com/products/fireplaces/gas-fireplaces/heatilator-novus-nxt-33.html). The AFUE represents a standardized test procedure that allows comparison of different heating systems. So these natural-gas fueled fireplaces are very roughly similar in efficiency rating to the one that I mentioned, but all would be significantly less than a condensing furnace.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
RGatesUser is Offline
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27 Aug 2015 08:16 PM

Lee, I understand what you are saying. When I read your post:

I think that it would be straightforward to improve the efficiency of the fireplace. Make the combustion volume smaller, increase the volume around the firebox and add heater exchangers around the outside to get the heat out of the firebox, and add a fan to get the heated air from the heat exhanger area to the room

 I though wow he just described, exactly, the same Heatilators that I installed in the 80' and 90's. LOL

Ron
MJGarciaUser is Offline
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14 Jun 2016 01:29 AM
Fireplace provide you with the most warm and peaceful place in winter. Installing a natural fireplace is a great idea as it comes with the heat efficient technology and can be installed almost anywhere in your home.
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14 Jun 2016 10:36 PM
And don’t forget masonry heaters...they run from the low to mid 90s for efficiency. Their high efficiency is largely derived from burning the wood at temps above 1500F and circulating the exhaust gas through a labyrinth of masonry before sending it up the chimney. As such, masonry heaters also pollute less than EPA certified wood stoves and they don’t have any creosote issues. Masonry heaters can be fired such that they are compatible with low load energy efficient buildings. Masonry heaters will often have heated benches and ovens too. The down side is that masonry heaters are rather expensive if not done as a DIY project. "Masonry Heaters - Designing, Building, and Living with a Piece of the Sun" by Ken Matesz is an excellent book on this subject.
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patonbikeUser is Offline
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29 Jun 2016 01:41 PM
I guess this is an old topic that got bumped but there are a couple gas fireplaces that are "90% efficient", not sure if that is AFUE or steady state.

Mantis by Empire is one.



Dana1User is Offline
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29 Jun 2016 04:09 PM
The Mantis has a condensing stack economizer system on the venting to bring it's steady state efficiency north of 90%.  I'm not crazy about automatically using the condensate water as active humidification though, as explained in one of the product brochures. 

Hopefully there's a way to disable that feature, and dispose of the condensate in some other way(?)  Active humidification is something to avoid in tight homes (even at IRC 2012 or newer code-min tightness.)
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03 Jul 2016 07:10 PM
I was considering the Mantis as we start our construction in Northern NM. But if you read reviews on the product, it appears to be noisy due to the exhaust blower, like a furnace. People complained it disturbed the ambience and also conversation. Not having witnessed one operating, I can't say just how loud it is, but I don't want to spend that kind of $ without seeing and hearing one in operation.
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