# Computing electric costs

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• posted on December 31, 2005, 12:40 pm
If vents are in attic or in walls that leak out the attic or a cold crawlspace yes, you loose a bit yes. Dont run it 24x7 and insulate , I insulated ducts and blew in foam in the walls above in wall registers, I blew out a few walls too with the expanding foam.
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<%-name%>
• posted on January 1, 2006, 12:46 am
m Ransley wrote:

I think you miss the point. A gas furnace requires 1 square inch of opening for a certain number of BTU's depending on the exact installation. If you have a furnace siting in the open in a very large space you don't have to have this ventilation because infiltration would be sufficient. But in normal situation you need the ventilation. In my case it is per 4000 BTU but not less than 100 square inches each for combustion and ventilation. The combustion air opening is required to be within 18 inches of the floor and the ventilation air is require to be within 18 inches of the ceiling. These vents are passive, you may not open and close them, they are open all the time as safety measures to prevent build up of CO and to eliminate build up of gas from leaks.
There is essentially nothing you can do to reduce the infiltration through the combustion opening and not way to reduce the heat loss through the ventilation opening. My contention is that this heat loss is never calculated in comparing electric heat with gas heat. The result is a bias in favor of gas heat because the electric heat will not have these losses. If you live in an especially cold climate, and the cost calculated for electric and gas heat are about equal, the real world cost of the electric heat will be lower than for gas heat.
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<%-name%>
• posted on January 1, 2006, 3:47 am
OK you are right to a point I think, Thats why I put in a condensing unit with cold air intake outside, but I would not have optioned or considered a window open type set up logical or necessary. To be sure I understand you every time the furnace runs you are sucking in cold air on a regular unit, but you say through a vent is necessary, or as in a window open. If your chimney won`t draw this could be nessecary right, but then the option is powervent exuast only. Or to be sure a blower door test is done to calculate air exchanges per hr. I had to go direct power vent everything after I put in new windows and all tyvek. unless its a million or 2m btu commercial boiler in a small room I dont see having a vent open to air as being an idea id even consider and I dought you could get a house tight enough to not draw in air through infiltration, it comes in every where, even the attic. Real tight houses need fresh air recirculators for good oxygen and reducing humidity, but heating systems through negative pressure generated by exuast get makeup air through everywhere even closed windows have infiltration ratings, because they leak. Direct vent condensing furnaces with outside air intake are common I think all condensing furnaces offer this option standard.
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<%-name%>
• posted on January 1, 2006, 7:15 am
m Ransley wrote:

I don't know how the most efficient furnaces are set up, mine is down a bit as are most peoples. And I'm not going through the whole Installation Instruction.
But lets just take the water tank which has an unpowered flue and a pilot light. The tank has a hole in the center above the burner, there is a gap between the tank the funnel which is the bottom of the exhaust flue which is about 2-1/2 in diameter. There is a louvered vent in the ceiling to the attic and a louvered vent in the floor to the crawlspace. When the burner is on, air is sucked from the adjoining rooms but mainly from the crawlspace in to the burner and goes up the exhaust pipe. Now what do you think the air flow is like when the burner is not on. Warm air naturally rises so warm air goes through the burner area but probably mostly through the gap at the funnel and goes up the flue to the outside. In doing this, it pulls air not only from the living space but also from the crawl space. Of course warm air also rises through the vent in the ceiling and it is much larger than the flue. All of these areas are much warmer than the outside so heat is lost and cold air from the outside is pulled in. BTW, the furnace is essentially the same except that it is a higher efficiency unit so it has an inductor fan.
Now if the system were completely sealed, and maybe high efficiency units are but I don't think they are, you wouldn't have these losses.
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<%-name%>
• posted on January 1, 2006, 3:59 am
Who requires this opening of venting 18 " off the floor and ceiling, not my furnace lennox. Ive never heard of a house having this open vent to outdoors set up. My apt building with a 1.6 million btu boiler has a window cracked 1" and the flame is adjusted by a tech with a Bachrach set up and he says oxygen, color and burner efficiency are tops. boiler is in a small room, heats 16 units steam heat. Infiltration does the rest.
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<%-name%>
• posted on January 1, 2006, 5:28 am

I wonder how much, if any, difference it would be with a larger vent instead of infiltration. I run a large boiler in one of our buildings and it has a motorized louver. You need a winter coat if you stand in front of the boiler when the blower is running for combustion. The boiler room is otherwise closed off by a door. This is in an old building with plenty of drafts and infiltration, but spread out over four floors and distances of 200 feet or so.
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<%-name%>
• posted on January 1, 2006, 5:57 am
Yours is cold, I packed a foot of insulation and its still real warm, Yes I need a vent but now I use a window 15 ft away .The proper way is exterior air or like what you have a motorised air set up is better than a window, its a Kewanee 2 pass
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<%-name%>
• posted on January 1, 2006, 7:23 am
m Ransley wrote:

Ok, my furnace is an Amana my water heater is a Brad ford White. The requirements are from the National Fuel Gas Code NFPA 54/ANSI Z223.1 Section 5.3
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<%-name%>
• posted on January 1, 2006, 11:25 am

More precisely, 1 ft^3 of gas has a heating value of about 1000 Btu, and burning it takes about 9.6 ft^3 of air, so a 50K Btu/h furnace burns about 50 ft^3 per hour with about 9.6x50 = 480 ft^3/h or 8 cfm of combustion air.

An average 2400 ft^2 US house leaks about 0.5x2400x8/60 = 160 cfm, 20 times more than 8 cfm, so vents for combustion air or gas leak dilution seem completely unnecessary, unless you install the furnace in a tight closet.
Nick
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<%-name%>
• posted on January 1, 2006, 9:09 pm
snipped-for-privacy@ece.villanova.edu wrote:

I'm not going to go through all the calculations, so I will assume they are correct, but see below.

I don't think 2400 square feet is the average house. Besides average means nothing, the median size house tells a lot more and I am sure it is well below 2400 square feet. Anyway my house is 1500 square feet and I don't think that it leaked anywhere near that amount of air (before installation of the gas furnace and water heater.
The rules as I read them are for a confined space and an unconfined space. Mine furnace is in fact in a closet, but even if it were outside the closet or the closet door was removed, it would still be categorized as a confined space and has to follow the confined space rules. That is because unconfined space is defined as that part that directly communicates with the furnace and is not equipped with doors. Much of my house would be behind those doors even though they are normally all open. It doesn't matter what the actual air flow facts are or what I think of the rules, the installers apparently followed the rules and the result is a lot more air infiltration and passive heat loss than before the electric furnace and water heater were replaced with gas appliances.
Just as a side note, I also would never again have a gas water heater because the thermostat has way too much range compared to an electric water heater. My electric water heaters always held the water within a very narrow range of temperature (say 3-4 degrees). My gas water heater can't keep water within a range of less than 10-15 degrees.
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<%-name%>
• posted on January 2, 2006, 12:26 am
Close your exterior air intake vents, im sure you will be fine. Air would not go up and out the chimney if there was not enough make up air, it would cool and downdraft. it will save you alot.
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<%-name%>
• posted on December 31, 2005, 1:34 pm
Heaters have two different types of efficiency ratings. One is called steady state efficiency, and one is called seasonal efficiency.
The only way to rate a heater is under laboratory conditions. If you take the exact same heater, and install it in two different homes, the season efficiency will change, depending on run time. Natural draft through a vented heater will cool it down when it isn't running.
The draft you are talking about is considered "infiltration", and is taken into account during a heat loss/gain calculation. It has little to do with the efficiency of the heater.

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<%-name%>
• posted on January 1, 2006, 12:31 am
Yes, but my understanding is the furnace manufacture calculates the heater efficiency without taking required ventilation (draft) into account. So when you compare a gas furnace which requires a certain amount of ventilation to an electric furnace which requires no ventilation, The results are skewed in favor of the gas furnace.
Bob wrote: