Ductwork info


  #1  
Old 01-06-04, 03:58 PM
appliancepresid
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Ductwork info

Hello All,
I have our new lp furnace 45kbtu upflow, needing ductwork installed new construction, no AC only heat and swamp cooler.

I had a company ( only one that would travel 54 miles one-way) come out and give estimate. He said they would use a 20x20x36" sheetmetal plenum. then run 18" insulated flex for 24' then reduce to 16" for 24' then reduce to 12" for remaining 12' of the main trunk. and do the take off's from the trunk.

Well I guess that sounded right , but then I asked about the use of the swamp cooler? water-moisture- mold growth...

He said it would not be that wet in the flex and it would be fine.

bid for the job was $1200.00 for flex I thought that was high.

So my main questions are does this all sound right and is mold going to be a problem.??

Location is North East Arizona and average winter temp. is 17 degrees low and 43 for high temp.

Almost forgot the return would be 18" flex all the way to furnace return sheetmetal plenum.

will that work????
Or should I do this my self ..

Thanks

craig
 
  #2  
Old 01-06-04, 04:59 PM
Ed Imeduc's Avatar
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Lightbulb Duct work

Sorry I would not put flex duct on a swamp cooler. No way. 60' of duct on a 45K BTu furnace I dont think the blower can do it ?????? ED
 
  #3  
Old 01-06-04, 05:50 PM
appliancepresid
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Hi Ed,
Thanks for the reply , I have asked this before on the flex but when the installer came out or estimater who ever they sent out to us, told us flex and they told us we only needed the 45k btu only 900 sq.Ft. home and 4 windows said it should heat very well and home has double pane low e windows and r19 walls and r19 ceiling ins.

The house is basically a shotgun home Straight line 16' wide 60' long looks like a singlewide mobile but it is a site built home. stick frame

The furnace is in the utility room at one end of the house. there was no room in center of house for furn. location.

Is there a fan upgrade for furnace,,,bigger blower or?

any other info.

My other thought would be to install a window evap instead of roof mount. and put in utility room to blow down through the rest of the house?
 
  #4  
Old 01-06-04, 06:24 PM
H
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payment

I'd withhold a good chunk of that payment till he can prove that will work....as they say, "I don't think that dog'll hunt!"
why isn't he using hard pipe? Especially on a run that long....I think the air will just dribble out.... but ya never know! Ask to see a similar job he did, and ask the owners how it works?
 
  #5  
Old 01-06-04, 06:36 PM
appliancepresid
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payment and ductwork

Thanks hvac0143,
I think he is using the flex to keep the cost down , but he never mentioned metal ducts except for supply and return plenums.

I thought the 18" dia flex was too large .

This company who was out was the only one who would come out 54 miles one way. We live in a very rural area.

bad thing is I listened to him the first time and bought the furnacealready a 45k btu 80+ afue upflow.

So what I am hearing is get a different dog but He is the only dog around. or would using smaller vent size work for air flow?/


Again Thanks
 
  #6  
Old 01-07-04, 08:23 AM
Ed Imeduc's Avatar
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Exclamation Duct work

Boy I dont know here a 18" pipe thats about 254" .We use about 240" for a good job on a 3 ton A/C. I dont think a blower in a 45k Btu furnace you have can get air to the end. yes some companys have a upgrade on the blowers dont know if you can get one for what you have. Like hvac01453 said I dont thing that dog will hunt. What do you have for attic can furnace go up there? swamp cool can you put it on the roof and blow down in a hall way? Not in the heat duct. The 45k btu should heat the home ok . In the ceiling we use a R -30 or better for insulation. ED
 
  #7  
Old 01-07-04, 11:32 AM
appliancepresid
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The Ductmare Continues

Hi Ed,
I had the company back out , they sent a different man out today , he said it is a small company with only three man crew. ( I think they are brothers)... Anyway he said if I dont use the evap in the ductsystem, size would go down to 12" main trunk and then use 6" take offs. and he also advised on moving the furnace to attic horizontal mount or in bathroom center of the house and not on the one end. He or the first guy never used any thing to determine duct size that I am aware of. only went by windows, location of windows and insulation r factor, but did not look in a book... If that means anything.

So now I am really concerned of this company and their installations.

I asked for a reference but was told they do not give out customer info due to privacy statements. ( crappy answer)

So I am thinking of doing this myself anything or any tips I need to know.

Apperantly there are no companies in the rural N.E. AZ area willing to drive 54 miles one way for a small ductwork job.


Thanks to everyone on the forum.
 
  #8  
Old 01-07-04, 12:02 PM
Ed Imeduc's Avatar
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Exclamation FURNACE

I would sure try and put it in the center of the home there by the bath or in the attic if you have room up there. 30 ft to the end of the home is a lot better than try and blow the air 60 ft. Ill bet you will save $$$ in just the fuel costIf you cango there by the bath set it up on a box and a grill out in the hall that will be the cold air return and go right up into the attic with ductboard there for the plenum. go www.llbuildingproducts.com it will show you duct work. also try www.aircondex.com/duct work ED
 
  #9  
Old 01-07-04, 02:48 PM
appliancepresid
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Once again, Thanks ED.

Two great sites for ductwork info.

I guess I will learn a new trade this month. installing ductboard.

one other question, is there a web site that sells duct board?
I have a home depot here about 50 miles away one-way but when I called he had no idea what i was wanting.

Could you tell me what tools would be needed for working with duct board. .
also you said ductboard can be used as the plenum , was that correct or would that be sheetmetal up to attic then go with ductboard for main?
 
  #10  
Old 01-07-04, 03:47 PM
binford
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ducts

Smooth metal ducts have less resistance to the air flow then the flex ducts. The flex dust are easier to install, because you get 25' in one box, they are insulated and can be easily snake around everything. Metal duct also get better flow because they are straighter, less up's and downs. They have industrial metal ducts, which are spiral wound and come in longer lengths. You want to go with a larger duct on long runs to ensure you get enough airflow. With a swamp cooler you normally don't use a ducted system, but it could be done. As for mold you live in a dry climate. If possible all furnaces are central located to help in the distribution of the air. A 60-foot run with your furnace would need a duct fan to boost the airflow so it could get enough air to the other end of the house..
 
  #11  
Old 01-07-04, 03:59 PM
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Duct boad

This is a ridgid fiberglass sheet that has an aluminum foil outer covering. You basically cut out V like knotches on the 90 degree angles and a rabbit I believe close. It's held together with pressure sensitive foil tape. Good thing is you can make any size you want. It's cut with a utility knife also. The stuff is very weak though, and it doesn't take kindly to being moved around, or the Christmas tree being layed across it. Get a heat load calculation done and then each room load requirement is the right way to do it rather than willy nilly. There are online sites that will let you do that I believe for a one time fee or it might be free. One of these guys may know the web site...
 
 

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