Additional attic insulation???

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My heat bills are about twice what neighbors pay in similar houses. And, I get ice dams. So it seems there is heat leaking up into the attic. I have soffit vents and a ridge vent. So I called 3 insulation contractors. One said the 6" that is in the attic between the 2x4 joists is fine and that adding more won't make a big difference. Two others wanted to add another 6" of cellulose. Pink stuff is more expensive and doesn't fill nooks and crannies as well.
My walls have 2" insulation which was standard back in 1970 when the house was built. I replaced all the windows with double pane vinyl windows. That was years ago and it did make a difference. I have a large aluminum frame slider that I cover with film for insulation.
I'm hesitant to spend $1600 on additional insulation if it isn't going to do anything. Can anyone suggest what is causing the heat loss? Thanks.
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6" of insulation is apx R 21, You dont say where you live or your Zone. Im Zone 5 to -20f, code is R 35 but optimal is apx R 50-60+. So unless you live in say florida or zone 9 more will help. What is attic sq ft. your areas low temps and Zone. Ice dams, may be air leaking up from he house, not enough venting, and lack of insulation.
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If the pink stuff is cut correctly, there's no reason it won't fill the spaces nicely. I haven't priced it in years (but I'm about to, this weekend), so I may be talking through my hat, but wouldn't it be cheaper to use the pink stuff, and install it yourself?
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Doug Kanter wrote:

ones. But that was suggested. Blowing in "pink stuff" (fluffy loose fiberglass) is preferred.
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Stubby wrote: ...

Either of those is good. I would want to do a little more investigation and see if you have an air leakage problem through the ceiling which may well be. You need to block that if you have it.
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Adding 6" of cellulose to the attic will help tremendously, so long as the soffit vents are kept open with some baffles. You'll add an average R value of 3.5 per inch of the cellulose so you'll increase your attic insulation from R-19 to R-40.
Other things you can do is move around your house with an incense stick looking for drafts. Seal up as many drafts and leaks as you can. There are professional services that will install a temporary blower into a doorway and will actually pull air from the house, creating a slight vacuum. Then they will actually test how much negative pressure is created and how much air volume is moving through the fan and from that determine how "leaky" your house is. They usually go around with a smoke pencil looking for leaks while this is happening too.
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louie wrote:

Which is what, about 3% difference in heat loss?

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CJT wrote:

Oh, and that's the heat loss through the attic, which is only a fraction of the whole-house heat loss.
As you can probably tell, I'm skeptical.

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Comfort is related to how quickly heat is being lost, and that's difficult to quantify. But, what if this mysterious comfort goal lies somewhere in that 3%? It would be a shame not to try.
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Doug Kanter wrote:

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Heat rises, insulating an attic is the cheapest way to save. 3% or whatever loss you figure you save on utilities and increase resale value. Adding 6" or R 21, well next year it will have settled 15-20% and be R 18. I put in R 100 it settled to R 80, an R figure that is optimal not what your local Minimum codes require. Through all I did I cut Ng by 60%, everything has a payback when it comes to insulation since standards do not reflect 1.70 a therm Ng, they are outdated from the 50s.
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CJT wrote:

But you are wrong. Since heat rises, especially in hot air heated houses,
the temp differential is much higher on the ceiling than on the wall. There is absolutely a point of diminishing returns, but if you do a real heat loss analysis on your house[it is not difficult, a pocket calculator is helpful, but not required] you will find that half the heat goes out the windows, and half the remaining goes out the roof. SO if you take that[gross] generalization, and you burn 1000 gallons of oil a season, figure 250 of it goes out the ceiling. At 2.50 a gallon that is 625 A SEASON. Are you betting on a return to 90 cent a gallon oil? I'm not. lets say with these made up numbers you have r20 in the attic, the numbers tell you that it should save you 125 gallons a year by going to r40.
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CJT wrote:

I think it will be more than a 3% saving. Say the temp difference from inside to outside is 50 degrees. The heat flow with R19 insulation is 50/19 = 2.6 in some arbitrary units like BTUs per fornight. With R34 the loss flow will be 50/34 = 1.8 in the same units. So in some amount of time the heat lost will be (2.6-1.8)/2.6 = 0.31 or 31 per cent less.
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Stubby wrote:

That's what I get for trying to do the calculation in my head.
Thanks for the correction.
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The additional insulation will make a difference. Use sheets of fiberglass or blown in biberglass and cover the joists completely. The more the merrier. Also, fix any air leaks. Insulate the hot water pipes and you should be able to turn down the setting on your hit water heater. The walls should be the last thing you try to insulate.
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snipped-for-privacy@gmail.com wrote:

water heater. That was a good idea back before we had the good insulation we do now days. Around here (Chelmsford,MA) waterheaters only last about 6 years because of the minerals. So I'd have to buy a new waterheater blanket with every replacement. The heat loss won't pay for it.
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On Tue, 20 Dec 2005, louie wrote:

Get one of those infrared thermometers and point it around the attic if you can move around reasonably in there. I have an Extech IR201 (one of the cheaper ones) but any brand will do.
Mine showed that my efforts to close the gaps around my vent stack penetration were unsuccessful by identifying a warm plume of air coming out around the insulation.
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Sounds like an interesting tool. Do you think it's sensitive enough to spot gaps in outer wall insulation, when used outside the house, or is that heat loss too diffuse for such an instrument? Short of ripping out pieces of wall, I'm not sure how to determine what's in those walls.
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On Thu, 22 Dec 2005, Doug Kanter wrote:

It is pretty sensitive.
Part of my house is a stone foundation and part is brick. It surprised me by showing that the (thicker) stone foundation insulated better than the brick by being 49 degrees (inside the basement) in general rather than 44 for the brick. I guess it makes sense in retrospect.
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Red brick may be absorbing more heat from sun; therefore record a warmer temperature. Sunbathing adjacent to a sunny brick wall on a cloud and windless winter day can be warmer for same reasons.
What I am getting at is to question what it is measuring. Three types of heat transfer exist - conduction, convention, and radiated. Is this only measuring radiated heat, and does measuring by this method provide an honest estimate of all heat lost? For example, are there locations where hands feel warmth but the meter declares a lower or same temperature?
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