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Old 04-04-2013, 05:05 PM   #31
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Humidity question


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What are you thoughts on reflective heat barriers installed on the attic floor? They said it prevents up to 95% of of heat loss and heat gain.

Works better and longer when put on the rafters. On the floor it will get dirty quickly and won't do much.

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Old 04-04-2013, 06:01 PM   #32
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Humidity question


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Except your last sentence or 2 has the low temp vapor going to the condenser coil then back to the compressor. Which is reverse of what happens.
The refrigerant leaves the evaporator as a low pressure low temp vapor and it has to extracted into the outside air via the condenser, which caused the temperature drop and change of state to a liquid, right? After that wouldn't it then go back to the compressor but I do see your point because the compressor can't have liquid in it. So, your saying when the vapor leaves the evaporate through the suction line it then enters the compressor and then the condenser?
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Old 04-04-2013, 06:02 PM   #33
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Humidity question


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Works better and longer when put on the rafters. On the floor it will get dirty quickly and won't do much.
If you put them on the rafters would that cause a possible heat moisture buildup in the attic in the winter though? If you put them on top of the insulation on the joists that would help prevent heat loss and heat gain wouldn't it?
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Old 04-04-2013, 06:08 PM   #34
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The refrigerant leaves the evaporator as a low pressure low temp vapor and it has to extracted into the outside air via the condenser, which caused the temperature drop and change of state to a liquid, right? After that wouldn't it then go back to the compressor but I do see your point because the compressor can't have liquid in it. So, your saying when the vapor leaves the evaporate through the suction line it then enters the compressor and then the condenser?

Right, it goes to the compressor first. Helps cool the compressor. And then the compressor pushes it into the condenser at a higher pressure so the heat can be released from the compressor.
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Old 04-04-2013, 06:13 PM   #35
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If you put them on the rafters would that cause a possible heat moisture buildup in the attic in the winter though? If you put them on top of the insulation on the joists that would help prevent heat loss and heat gain wouldn't it?

On the rafters they prevent the heat from entering the attic. The attic is still vented, so no moisture build up problem. No heat build up problem either.

On the floor, the attic would still get very hot. And radiant barriers have a low R value, so you would still get a large heat transfer into the home(although not as much as without the barrier).
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Old 04-04-2013, 06:24 PM   #36
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On the rafters they prevent the heat from entering the attic. The attic is still vented, so no moisture build up problem. No heat build up problem either.

On the floor, the attic would still get very hot. And radiant barriers have a low R value, so you would still get a large heat transfer into the home(although not as much as without the barrier).
For instance I know your not supposed to insulate the rafters because it causes a warm roof deck so I am thinking the radiant barrier would cause the same issue because that cool air in the attic would be blocked by the radiant barrier. You seem what I'm saying?
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Old 04-04-2013, 06:39 PM   #37
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Roofs are being insulated with spray foam. Shingle temp increase is not enough to harm them.

A radiant barrier doesn't cut off air to the roof. Its applied to the rafter, not the roof itself.
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Old 04-04-2013, 06:59 PM   #38
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Roofs are being insulated with spray foam. Shingle temp increase is not enough to harm them.

A radiant barrier doesn't cut off air to the roof. Its applied to the rafter, not the roof itself.
Everyone I have talked to said you never insulate the rafters. That would cause the underside of the roof to be warm and caused possible moisture and ice dams. I don't understand why your saying roofs are being spray foamed.
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Old 04-04-2013, 07:13 PM   #39
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Everyone I have talked to said you never insulate the rafters. That would cause the underside of the roof to be warm and caused possible moisture and ice dams. I don't understand why your saying roofs are being spray foamed.

Cause they are. You should talk to some companies that do spray foaming.

How would a radiant barrier cause a roof to be warm that it caused a moisture problem. Your not putting the barrier against the roof. Its still vented.
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Old 04-09-2013, 05:52 PM   #40
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Yep, been in the trade 38 years.

There are several HVAC tradesmen on this forum. We will all help if we can.
Hi,

I have some venting questions about certain appliances. A furnace can be a natural draft vent, which is B-vent that is a Category I. I was told Category II is not used anymore. Category III is stainless steel venting under positive pressure and can be terminated horizontally and vertically. I think this is for hot water heaters and fireplaces. Category IV is direct venting where you can use PVC with a furnace. My confusion is if there is a Category IV with like a hot water heater or furnace or is it simple just a Category III? Also, because of the low gas temperatures in direct venting can you use an existing chimney or run it through the roof?
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Old 04-09-2013, 06:21 PM   #41
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Furnaces, boilers and hot water heaters are all made in a at IV version.

Cat IV can't be vented into a standard masonry, or B vent chimany. Due to condensation.
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Old 04-09-2013, 07:41 PM   #42
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Furnaces, boilers and hot water heaters are all made in a at IV version.

Cat IV can't be vented into a standard masonry, or B vent chimany. Due to condensation.
Furnaces have natural draft b-vent, right? My hot water heater is a natural draft. Also, the III version uses stainless steel and is that only for fireplaces and tankless water heaters?
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Old 04-09-2013, 07:45 PM   #43
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Natural draft furnaces can be be vent.

Stainless is used on some boilers also.
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Old 04-09-2013, 09:15 PM   #44
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Natural draft furnaces can be be vent.

Stainless is used on some boilers also.
When you have a class three stainless steel venting that is power vented and can be vented like a direct vent, right? Do all Class 3 and 4 utilize heat exchangers?
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Old 04-10-2013, 02:50 PM   #45
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When you have a class three stainless steel venting that is power vented and can be vented like a direct vent, right? Do all Class 3 and 4 utilize heat exchangers?
If your referring to secondary heat exchangers. Boilers don't use a secondary heat exchanger. But all cat III and IV have heat exchangers. other wie they would be direct fired, and not be vented.

All cat III and IV appliances are positive pressure vent systems. So they are power/direct vent systems.

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