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Old 12-20-2011, 09:16 AM   #16
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What Should Furnace Supply Air Temperature Be


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Originally Posted by Jackofall1 View Post
Really, that means that I should open up a duct replacement shop
Im no heating contractor but glad someone else found a little humor in that. That why I threw in a couple of

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Originally Posted by Jackofall1 View Post
Sure look like there are alot of heat runs for a furnace of 96.5K output, what is the size of the home you are heating, did the installing contractor do a Manual J to size the furnace properly.
House is about 2800 ft2. There are a total of (25) 6" takeoffs from the main trunk line. (10) feed 1st floor, (10) feed 2nd floor and (5) feed basement.

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did the installing contractor do a Manual J to size the furnace properly.
Do not know who the contractor was. Been in house for 2 years but was built in 1997. Can you elaborate on what is needed for this.


Also this morning I knew the furnace would run for at least 20 minutes to bring house up to temp from the night's setback. So I set my thermometer in the closest register to plenum and output air read 126 F. Input air was probably 65 so about a 60 degree rise that falls within the parameters.

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Old 12-20-2011, 09:21 AM   #17
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What Should Furnace Supply Air Temperature Be


Sounds like your furnace is developing the necessary temp rise and you mentioned 20 minutes for the house temp to increase to the Tstat setpoint this morning, which sounds good in my opinion, you didn't mention the increase in setpoint.....65 to 70??

Are you in southern Ohio?

A "Manual J" is a comprehensive spread sheet which totals all heat losses in a structure, which is then used to size a furnace accordingly.

Mark
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Old 12-20-2011, 10:42 AM   #18
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What Should Furnace Supply Air Temperature Be


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Really, that means that I should open up a duct replacement shop, cause there isn't an installation here that insulates ducts. If you are down south I could see where condensation would form on the outside of the duct when using AC, but not on the inside.

As well as heat loss of those 6" round ducts is lost to the basement, heat rises which warms the floors above, which warms the room above the floors.

Yes if your basement walls are not insulated there will be some heat losses, but nothing really to be gained by insulating the ducting in your basement.

Sure look like there are alot of heat runs for a furnace of 96.5K output, what is the size of the home you are heating, and did the installing contractor do a Manual J to size the furnace properly.

Mark

I am down south and yes, everything and I mean everything (no basements,attic) is always insulated and again, "usually much more humid air" and yes, inside and out.
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Old 12-20-2011, 10:46 AM   #19
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What Should Furnace Supply Air Temperature Be


All metal duct is insulated in both residential and commercial, return plenums and supply plenums as well. Internally most times on rectangle duct and externally on round.


Always down here.
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Old 12-20-2011, 10:54 AM   #20
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What Should Furnace Supply Air Temperature Be


The one home I have ever been to that has a basement here had insulated metal rectangle and round cut running thourgh it, none of this "heat rises and rots your floorboards" stuff happening down here.

It simply can not or will not work uninsulated.

You should move down here and then start a duct insulation company but you'd go out of business due to the fierce competition from people who actually know what they're doing.
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Old 12-20-2011, 11:09 AM   #21
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What Should Furnace Supply Air Temperature Be


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Are you in southern Ohio?
northern ohio...15 miles south of Cleveland
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Old 12-20-2011, 11:33 AM   #22
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What Should Furnace Supply Air Temperature Be


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You should move down here and then start a duct insulation company but you'd go out of business due to the fierce competition from people who actually know what they're doing.
Doc.... my ducts are about 14 years old. Some can be seen in the 2nd photo on my post #1. As you can see they are uninsulated. There are no signs of rust either.

In your opinion when should I plan on replacing them due to rust
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Old 12-20-2011, 12:05 PM   #23
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What Should Furnace Supply Air Temperature Be


Just goes to show you the different concerns for different areas of the country. Doc's obviously working on A/C 90% of the time in a much different climate zone than Ohio.

Some of the rest of us would have a much different split of heating to cooling demand, at a greater variation of humidity and construction methods. Insulating ductwork in my area is rare, but 99% of houses have a basement, and most of those are finished as living areas.
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Old 12-20-2011, 12:06 PM   #24
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Originally Posted by Doc Holliday View Post
The one home I have ever been to that has a basement here had insulated metal rectangle and round cut running thourgh it, none of this "heat rises and rots your floorboards" stuff happening down here.

It simply can not or will not work uninsulated.

You should move down here and then start a duct insulation company but you'd go out of business due to the fierce competition from people who actually know what they're doing.
Really the heat doesn't rise south of the Mississippi? Now that is some crazy stuff there and heat is usually used to drive off moisture don't understand the rot thing, not in the least bit.

But yes in the south, because of cooling and high humidity ducting will reach dew point and condensate if not insulated...

As for experience thats a rather bold statement as you have no idea who I am or what my capabilities are...
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Old 12-20-2011, 12:10 PM   #25
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What Should Furnace Supply Air Temperature Be


If you are interested hammerlane (I take it you like to go fast by that name..) there are Manual J calc sheets available on the web, just search will cost you about $40 for a single use copy, but I guess as long as your furnace keeps up on the coldest days you would be fine.

Believe it or not it is more efficient to have a furnace run for longer cycles or even continuously for that matter as you don't lose on the heat-up of the heat exchanger on each new cycle.

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Old 12-20-2011, 12:26 PM   #26
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What Should Furnace Supply Air Temperature Be


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Believe it or not it is more efficient to have a furnace run for longer cycles or even continuously for that matter as you don't lose on the heat-up of the heat exchanger on each new cycle.
Mark
Thats easily understandable.

Also I watched a manual J calculation video from here:

https://www.acca.org/acca-files/MJ8ae.swf


I don't think I want to go any further than what I have already discovered.

I'm thinkin/hoping the current furnace will last at least a couple more years. I shop vac the inners at the beginning of each heating season and change the filters regularly. I installed an hour meter I had last year and tied it into the gas valve. I change the filter every 125 hours. When I need a new system I'll make sure the contractor provides a Manual-J spreadsheet.

Thanks for all the comments to everyone even you Doc.

All have a good Christmas.


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Last edited by hammerlane; 12-20-2011 at 12:49 PM.
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Old 12-20-2011, 06:27 PM   #27
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What Should Furnace Supply Air Temperature Be


Okay, so I realize things are different in geograhical regions, why I originally said (again), "in most cases more humid" but I guess most should've just been down south by the gulf.

Sill, to myself it makes no sense to have heat escape thourgh exposed metal duct to then try and make it up through floor for heating a roOm. Sounds highly inefficient compared to delivering the full potential of heated air through a well insulated duct into a well insulated roOm via the vent.

Sounds bassackwards but that's just me from way down here in Insulationville, USA.
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Old 12-21-2011, 08:48 AM   #28
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What Should Furnace Supply Air Temperature Be


Hea Doc your on the right track. With energy audit coming in more and more eveyone will have to insulate more and start sealing more no matter what region you may live in, if we can get the envelope to 3.5 air changes per hour per BPI standards then people would not have so many ?s about the house being to cold. Keep sealing and insulating those ducts. Your good at what you do keep it up.
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Old 12-21-2011, 09:09 AM   #29
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What Should Furnace Supply Air Temperature Be


I see everyones point. But look at this angle:

What is the "main"point of insulating? Probably to save money on fuel costs. But you cannot win. You will not save in the long run.

If we keep insulating and using less fuel, the gas or electric company just raises their rates.

Say "Natural Gas Company OHIO " sells 1,000,000 CCF of gas annualy at $1.00 per ccf. So their revenue is $1,000,000 a year.

When customers start insulating making their home/businesses more efficient "Natural Gas Company OHIO" may now only sell 900,000 CCF of gas. So to get at their $1,000,000 revenue mark they now charge $1.11 per CCF.

So in the long run THE MAN wins again.

The above scenario occurred with the Cleveland water Department....people using less water(low-flow shower heads, low usage toilets, etc)

http://blog.cleveland.com/metro/2011...tment_has.html
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Old 12-22-2011, 12:04 PM   #30
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There is a different approach for utilities if the state legislatures approve, called decoupling. It allows the electric utility company to make profits from reduced consumption. Currently, as consumption increases, the utility has to build a new plant and pass the costs to consumers, with no incentive to stop this cycle.

Decoupling looks at the cost of the plant and in effect says, make money by helping your customers save money, and save the money of building the new generating plant.

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