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## Help with HVAC-CALC home owner load calcualtion

Hi All,
I'm trying to do load calculation with HVAC-CALC software. As a new home owner and a first time home owner I'm trying to understand all the aspects of the calculation. The first problem I've encountered is the duct insulation. The presenter of the learning video on the HVAC-CALC website selects R6. How can I check my duct insulation rating?

Thanks

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Actually I'm not even sure I need to add the Duct component to the load calculation. The guy on the video says "if the furnace was in the basement and the duct vent was in the condition space we wouldn't add the Duct component at all". So I guess my first question is what is this duct vent and where is this condition space? My furnace is located in the basement and I don't know of any additional vents.

For those of you who's interested to watch the video, here is the link:
http://www.hvacmovies.com/movies/wholehouse/wh3a.html

Thanks.

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I'm kind of answering my own questions here. I think I don't need the Duct component because the furnace is in the basement and the duct is inside the house so it doesn't contribute to the load.

4. If the duct is in conditioned space. It is not part of the load calc.

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Originally Posted by beenthere
If the duct is in conditioned space. It is not part of the load calc.
Thanks beenthere,
I wasn't sure what the conditioned space is. I figure it's the space that is already a part of the calculation.

Now, how would I know the cavity insulation rating? The guy in the video selects R-13, the software manual reads "Select R-11 (3 ½ in.). This is the standard insulation in the wall cavity of a wall with 2 X 4 studs". I selected R-11.

6. Unless you know different.
Use R11.
Pretty standard here for 2X4 walls. The batts could be rated at R13. But, when you allow for the studs. You lose some R value in the wall.

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Okay I guess I'm done. Hopefully I did the numbers correctly. The only thing that I wasn't sure of was the Ceiling insulation. Mine is R-32. The available selections were 30 or 38, so I selected 30. I got the following results:
Design Conditions: Toronto
Indoor: Outdoor:
Summer temperature: 75 Summer temperature: 87
Winter temperature: 70 Winter temperature: -8
Relative humidity: 55 Summer grains of moisture: 95
Daily temperature range: Medium

Building Component

Infiltration 15,296
Walls 19,746
People 0
Windows 3,588
Misc 0
Ceilings 2,291
Floors 5,678
Doors 1,120
Skylights 0
Glassdoors 0
Fireplaces 4,370
Duct 0

Whole House 52,089

So by adding 20% safety factor I get 62506 BTU. If a 96% efficiency 60000BTU furnace output is going to be 57600 BTU (right?) should I consider a 70000 BTU furnace or 60000BTU will be good enough? If 70000, will it be noisy considering the ducts are not big enough (as somebody told me)?

Thanks.

8. I wouldn't add a 20% safety.

60,000 should be plenty.
Yes, a 70,000 could be loud with under sized ducts.
A 70,000BTu 95% would need 1026CFM for a temp rise of 60° across the heat exchanger.
A 60,000 BTU 95%, only needs 879 CFM for the same 60° rise.

That air flow difference can make your ducts system louder.
Or, the ducts could be small enough, that the furnace can't move enough air. And the furnace rides, or trips the high limit. Which would cause high heating bills.

9. Go one step better for the furnace, install a two stage unit. This way if you choose a 70k btu, it will mostly run on low fire. Personally I would not add 20% factor, just guess low on items you are not sure about. Usually I like to size condensing furnaces as close to the heat loss as possible. I find most folks tighten up the house and add insulation which reduces the heat loss, making the furnace over-sized, if they start out with too much furnace input to begin with.

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I have interviewed 8 contructors. The one that I feel most comfortable with sells Bryant Trane and Rheem. I like the features that come with 60000 BTU Bryant 355AAV and Evolution Thermostat. This was also the least expensive option between the 3. I was thinking about York YP9C but couldn't find a contructor that I can trust. Then I had a few contructors that offered Amana/Goodman but it only comes with 70000BTU which seems too much according to my load calc. So that leaves me with Bryant I guess.

11. a 2x4 wall in Canada is R12

most common furnaces I used to sell in T-Bay were 60 and 75K, -8F sounds pretty chilly for Toronto

something built in the early 70s in T-Bay would be about 2000 sqaure feet including basement to have a 52000 heat loss

I would pass on the two stage myself, will have good results with a single stage sized on the money.

As beenthere has warned you, the newer furnaces will probably move about 50% more air than the older furnaces with a pilot light.

If your old furnace has a pilot light, you should consider upgrading mechanical ventialtion now

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Originally Posted by Carnak
a 2x4 wall in Canada is R12

most common furnaces I used to sell in T-Bay were 60 and 75K, -8F sounds pretty chilly for Toronto
I was going by max temperature both ways. Last year we had a few weeks that were at about -8F. Should I put the average temperature instead?

something built in the early 70s in T-Bay would be about 2000 sqaure feet including basement to have a 52000 heat loss

I would pass on the two stage myself, will have good results with a single stage sized on the money.

As beenthere has warned you, the newer furnaces will probably move about 50% more air than the older furnaces with a pilot light.
The house was build in 1987. Is moving 50% more good or bad? Will a single stage furnace move less air?

If your old furnace has a pilot light, you should consider upgrading mechanical ventialtion now
Okay the more I hear from you guys the less I want to replace my working furncace at all . I was trying to get some more camfort, filter the dust with a newer cleaning system, reduce the noice and save some money on the bills. But really, reading on forums about all the troubles people got into with the new furnaces and understand how careless most of the contructors are made me think - may be I should wait until my old furnace reeeeeely breaks.

Yes, my old furnace has a pilot light. What does it mean "upgrading mechanical ventilation" and how is it related to the pilot light?

thanks.

13. For houses OF is a typical outdoor design condition in TO area, for a commercial building they would use -3F.

A new furnace will move more air, more air in same ducts means more noise

When you have a pilot light you usually have what is called a drafthood, an opening that lets room air get drawn up the chimney with the products of combustion. When the furnace is off in the winter, as in inbetween heat calls, room air still goes in that draft hood and up the chimney.

So in cold weather that chimney ventilates the home 24/7. A home always has the same amount of air in it, so when room air goes up that chimney, cold dry outside air will infiltrate in to replace it.

Cold air holds little moisture so this tends to and keeps the home dry in the winter, even to the point of needing a humidifier.Get the old wives saying 'gas heat is dry heat' because of this.

When you upgrade the furnace there is no longer a draft hood and you lose that 24/7 ventilation effect in the winter. It is not uncommon after upgrading a furnace (without a ventilation upgrade) that the house suddenly becomes too humid in the winter and you get a problem with condensation on your windows.

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