New Home Begins

   / New Home Begins #401  
And that's probably about the best you can do - ask them and ask to see some examples of already built houses like this in your area. Since you just got a bit of snow recently, it should be a very good time to look at an existing house built the same way and see what the roof looks like for melting patterns, if any. That will tell you exactly what you need to know.
 
   / New Home Begins #402  
Tom,
As you can tell, we all want to help you spend your money! When building my house, TBNers provided valuable input. However, if I had done everything that was recommended, the house would have cost $200/SF. You have to pick and choose and just make your best judgement call. You also have to balance getting quality work and keeping from running off all your subs. At least when you make your your choices, you are making well-informed decisions and are not acting out of ignorance.

Obed
 
   / New Home Begins #403  
I have a "hot" roof, ie: icynene spray foam insulation directly against the underside of the roof. I also have a small attic below the insulation. Anyhow, have lived here for 8 years in the extreme South Dakota temperatures and haven't had any issues whatsoever. Once in awhile when the weather is just right, I can see a slight pattern on the roof caused by the wooden rafters but it is minor and not very pronounced. Don't know if this helps or not and was initially freaking out about having a "hot roof" but haven't had any issues.
 
   / New Home Begins #404  
I have an outside air heat recovery system. It essentially is a joke and if I ran it 24/7 like I supposed to would get zero benefits from my insulation. Could as easily leave a window open. It does strip some heat/cool energy but I would guess in the range of 10%.

Are you sure your system is running OK? I have a 50cfm heat recovery system. It's supposed to be 80% efficient. Right now it's about 15F outside and the inside supply doesn't feel noticeably cool. I also have inlets in the basement to let in enough air to make up for the basement negative pressure (stack effect). These are U-tube arrangements (trapped) so I only get enough air to equalize the pressure. That air feels very cool but it's a very small flow rate.
 
   / New Home Begins #405  
Are you sure your system is running OK? I have a 50cfm heat recovery system. It's supposed to be 80% efficient. Right now it's about 15F outside and the inside supply doesn't feel noticeably cool. I also have inlets in the basement to let in enough air to make up for the basement negative pressure (stack effect). These are U-tube arrangements (trapped) so I only get enough air to equalize the pressure. That air feels very cool but it's a very small flow rate.

Have the same set up...go measure the temperature of your exhaust air sometime on a cold day. I actually plugged mine into a timer that allows it to run for 4 hours every day during extreme temperature episodes. Well it transfers some heat/cool but as far as the 80% efficient...clever marketing.
 
   / New Home Begins #406  
Dave,

I appreciate the insight and I am going to consider it. And I do not want to start a war like the earlier concrete fiasco several pages back. :D

Since I am the one responsible for the comments about your concrete, I apologize for creating a fiasco. That was not my intent.

Eddie
 
   / New Home Begins #407  
Have the same set up...go measure the temperature of your exhaust air sometime on a cold day. I actually plugged mine into a timer that allows it to run for 4 hours every day during extreme temperature episodes. Well it transfers some heat/cool but as far as the 80% efficient...clever marketing.

Well, you got me curious. It's warm here today, up around 35F outside. The outside air supplied into the house is 68F. The inside air that I'm exhausting is about 72F. I'd have to go outside to measure the exhaust temperature and I don't feel like tromping around in the snow right now, but it looks to me like I'm around 80% from the numbers I have. That 33 degree temperature rise is coming from somewhere.
 
   / New Home Begins
  • Thread Starter
#408  
Since I am the one responsible for the comments about your concrete, I apologize for creating a fiasco. That was not my intent.

Eddie

Eddie,

I was kidding and I certainly was not offended. I only meant that it sparked quite a bit of discussion on lots of related points ... warm vs cool temps for curing, slumps, rebar vs wire, etc. Please, I have enjoyed it by seeing so many TBNers participate. What more can you ask for.

In hindsight, I should have put the word fiasco in quotes.
 
   / New Home Begins #409  
Well, you got me curious. It's warm here today, up around 35F outside. The outside air supplied into the house is 68F. The inside air that I'm exhausting is about 72F. I'd have to go outside to measure the exhaust temperature and I don't feel like tromping around in the snow right now, but it looks to me like I'm around 80% from the numbers I have. That 33 degree temperature rise is coming from somewhere.

Seems like at perfect heat transfer the incoming air would hit the midpoint of the two temps (incoming/exhaust) and the outlet air would also be at the midpoint of temps. That seems to me to be 50% efficient at the best possible transfer rate.
 
   / New Home Begins #410  
Seems like at perfect heat transfer the incoming air would hit the midpoint of the two temps (incoming/exhaust) and the outlet air would also be at the midpoint of temps. That seems to me to be 50% efficient at the best possible transfer rate.

These heat exchangers are counterflow, not parallel flow. The theoretical maximum efficiency on a counterflow heat exchanger is 100%, although in the real world it's obviously less. To understand envision this as a very long pair of tubes fastened to each other. The very start inlet air (say 30 degrees) is picking up heat from the very last of the exhaust air path. The very last of the inlet air path is picking up heat from the very first of the exhaust air path (say 70 degrees).
 
 
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