house always heats up


Old 08-04-09, 06:06 PM
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Join Date: Aug 2009
Posts: 1
house always heats up

Hello all. I am not sure if this is in the right spot. I own a small bungalow in Hamilton 800 sq f. The house is circa 1920. Since moving in 3 years ago I have done and had a lot of work done. The roof is new as well as the furnace, all the windows are under 10 years old and are vinyl.

With the government energy programs I decided to do as much work as I could. Now even before any insulation, this house has always been very easy to heat. There were a few cold spots but still very good. Because the house is small and on one floor I decided to try the largest window unit I could find to cool the place. This has always worked well here, I set it at 19c and that is where the house stays. Before any work was done, the energy auditor rated the house a little below normal as far as the wind test went. After the work the house is now above average. The inspector also mentioned that the air exchange was still within safe limits.

The problem has always been that I run the AC all spring and summer. Even if the temperature outside goes down to 10c at night, the inside temp will be 23 or 24 windows wide opened. I typically never had to put the heat on until December. So I thought after having the walls all insulated and the attic blown to R 40 with polyurethane insulation that my cooling problem would be fixed. (Attic had no sofit vents so I installed them aswell as lots of roof vents and the attic is not to bad hot.) There is very little cross ventilation in the house even with the windows open. But how can I turn the AC off at 19c and itís the same temp outside, yet withing Ĺ the inside temp has gone up by 4 c? I know this is long, but any advice would be greatly appreciated.

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Old 08-05-09, 06:51 AM
Join Date: Nov 2001
Location: USA
Posts: 1,873
Insulation retards heat flow and as part of doing this insulation will retain heat for a period of time. Whereas when you did not have insulation in the home the heat the house collected during the summer day would dissipate quickly. The 3 mechanisms for heat transfer are Conduction, which insulation addresses, Radiant, the hotter an object is the more heat it will give off and the closer you are to that object, the more heat one will sense, and Convective, how air will absorb and expel heat from objects it comes in contact with.

Regardless of the situation all 3 mechanisms are involved, the only difference is one will dominate the other two. If one was to address the dominate heat transfer like Conduction by installing insulation, one of the other mechanisms or both will become dominate and will influence comfort. While these processes are considerably more complicated than what is described here, the aforementioned should be sufficient for you to understand what is happening in your home and the best way for you to address the problem.

The second Law of Thermal Dynamics, "High to Low" states that an object of higher temperature will give heat energy to objects of lower temperature and not vice-versa. This rule also applies to Pressure and Humidity. There are very few exceptions to this rule.

If you apply all this to your situation, it explains the conditions before and after the installation of the insulation. Before as the temperature outside dropped the temperature inside the house dropped with it. After as the temperature outside dropped the temperature inside did not because the insulation is retaining the heat it collected during the day. The result is the discomfort you are now experiencing.

Bungalow roofs usually are difficult to ventilate properly. Though the primary purpose of attic ventilation is to bypass the low vapor permeability of roofing materials, it has a second purpose which is heat extraction from attic insulation during the summer. It does this through the mechanism of Convection. This is important in your situation because of the amount of heat your roof collects during the day that is transferred to the attic insulation. Which retards that heat from entering the house but at the same time retains a lot of the heat. Because of this if you were to measure the temperature of the insulation in the attic at night, it would be considerably higher than the temperature outside.

The temperature inside the attic insulation and your proximity to that insulation has caused the Radiant heat transfer mechanism to dominate which has resulted in your discomfort.

You will see some discuss Radiant Barriers, unfortunately they do not address the primary purpose of attic ventilation. In my opinion a "Cold Roof" is your best option. If you don't know what that is, I will explain it to you.

And you thought your post was long.

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