Old Furnace Power Vented

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Old 04-18-04, 06:41 AM
jvinyard
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Old Furnace Power Vented

I have an existing house with a furnace built in 86, so I don't think that it is that efficient. It currently has a blower on the exhaust vent because it goes horizontally for about 5 feet. There is a label on the blower that states that you can run horizontally for 30 feet. The vent currently ends into a brick chimney with the hot water heater.

I want to use that old brick chimney for a gas insert and so I am going to line it with the pipe required for that and need to re-direct the furnace and water heater out the wall.

I am going to replace the water heater with a direct vent. The installation of this states to use PVC and just go out the wall and cap it. I don't have any problems here.

For the furnace, I am not sure if I can just go out of the wall and then stop with a vent cap, or if I need to elbow and then go up along the wall until I clear the roof. How do I know which is correct/safe? The pipe that is currently coming out of the furnace is just 3 inch single wall pipe. Do I have to use double wall if the pipe is exposed?

Also, do I have to bring combustion air into the furnace if there isn't any coming in now?

The furnace is a Snyder General, and I cannot find any information about the installation of the unit.

Thank you!
 
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Old 04-18-04, 08:00 AM
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Hello: jvinyard

No double wall vent pipe is needed nor should be used on the furnace. A single wall vent pipe the exact same size should be used or added to the existing flue vent pipe.

Once the addition to the furnace flue pipe is outside the outer exterior of the house, it must be plumbed up to and above the roof line. Usually 20 inches or about give or take some. Check with local codes in your area.

No double walled flue pipe should be used in conjunction with the existing flue pipe on the furnace. Simple use an exact same type of flue pipe and extend it to the location out the wall.

Do not increase nor decrease the pipe diameter size. But do insure the rise angle is maintained to the exterior wall. Local codes may also require the pipe be secured to the exterior at specific footage intervals.

At no location should the flue pipe come into contact with any exterior houses surface. An insulation bucket will also be needed at the locate where the flue pipe passes through the wall.

The need for combustion air (Makeup Air) should not nor is it likely to be needed with the existing two appliances. The area (room) where those two apliances are currently has to have vents to the outside to already be bring in fresh air for combustion.

Premise here is the 1986 built home already meets all the existing codes and was built to meet them. Especially, if the house is a tract home and or was built by a licensed building contractor.

That info, if house is a one of a kind custom home and not a tract home etc, if info not known, can be obtained at the city office.

Suggestions:
Check with the building and or safety departments for code requirements and strickly adhere to them.

Also check with local heating agencies for professional advice. Which is likely to be obtained if you make the materials purchases at those type of stores instend of the "Big Box" stores.
 
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Old 04-18-04, 12:32 PM
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my 2 cents

in applications i have seen and installed, with relation to an 80% furnace with a sidewall flue termination, a power vent is required at the termination. it is in fact part of a hood assembly that mounts into the wall. because of the fact the major part of the flue run is horizontal (slower flow than vertical) and we do not want the flue gas to cool to the point of condensating inside the pipe, i would think B vent may be a proper selection. this is what we do in georgia, many areas do things differently, so i can only comment on what is prevalent in my area. those vent hoods are pricey...200 plus or so wholesale.

go to www.tjernlund.com



this is what we use
 
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Old 04-18-04, 01:05 PM
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Thanks hvac4u

Excellent web site with plenty of pics and explainations, etc.

Side Note:
Out this way, West end of this rock we call Earth, there is no requirement for an assist power vent on the flue on any appliances nor already equipped power vented appliances I have seen or am aware of.

Which indicates codes and methods of installations do vary from state to state and area to area, etc.

Other rules apply by code.

Example:
The constant rise of the flue pipe applies always. Only exception I am aware of is the dual wall vents for side vented water heaters.

The info exchanged here is a perfect example of how codes and installations methods apply and vary. Sharing such provides valuable information for the learning process between us all and all readers as well.....
 
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Old 04-18-04, 02:40 PM
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another perfect example of how things are done differently from region to region.
what we do and how we do it are governed by the local authorities, in our case, county building inspectors. we know what "will fly" code wise here, and stay within those parameters.
i worked in south florida for 2 years in the late 80's, almost like a different trade, standards were VERY different.
as sharp advice mentioned, get with the local inspection dept, see what they require in your area, and work within their rules and regs
 
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Old 04-19-04, 07:10 AM
jvinyard
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Thanks and followup...

Thanks for the replies... Very helpful information!

You said that "At no location should the flue pipe come into contact with any exterior houses surface" Why is this?

You also said that "An insulation bucket will also be needed at the locate where the flue pipe passes through the wall." Is this just so that the pipe doesn't touch the walls?

The house was built in 1947. There isn't any venting for outside air for either unit currently. They are also in two different rooms. Can I just add another 3 inch pipe that terminates at the wall, and is attached to the intake on the power vent already installed on the furnace?

The new water heater I am going to install requires two pipes, one for combustion and one for vent. They are both PVC pipe.

If I used the Tjernlund system, could I terminate at the wall and not be required to rise above the roof line? 15 feet of pipe and a cap is less money and will get the job done. I like that better.

I did check with the local inspector. He thought that I had to go above the roof to, but told me to check the installation manual with the furnace. I am fairly confident that if I do that, I will be safe (most important) and will pass inspection (also required).

Thanks again.
 
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Old 04-19-04, 12:00 PM
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flue pipe, when single wall require 6 inch clearance to combustible materials, double wall "B" vent requires 1 inch clearance. not sure what sharp is referring to as a "bucket", but possibly he means a sleeve in the wall larger than the pipe, and insulated wiyh non combustible insulation.

the vent hood is the termination, it does not rise after exiting the wall.
 
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Old 04-20-04, 04:44 AM
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hvac4u

Yes. Ceiling bucket is the insulated part the flue pipe passes throught so the hot flue pipes outer surface does not directly come into contact with any potentially flameable surface.

They are used when the flue pipe passes through a ceiling or the roof, etc. Required be code locally. Also required even when a flue pipe passes throught a stucco, cement, block wall, etc.

Only exception is a double walled flue pipe. Since the fresh air intake is in the outer pipe and the hot flue pipe is on the inside of a double walled intake exhaust pipe. Thereby having a built in type of insulation of it's own.

Codes and rules do vary widely from state to state and even county to county. Our fire prone areas also vary codes from those in the suburbs and cities. Much stricter and more well enforced. Different strokes for different folks...
============
jvinyard

Yes. Hot flue pipe cannot come into direct contact with structure. As noted above, your local codes may require insulation buckets where ever the flue pipe passes throught any part of the structure. Inquire and adhere to those requirerments.

Very possible a home built in 1947 did not have a requirement for fresh air intake for combustion. However, since burning requires air for combustion, air has to come from some place.

Using the inside air is not a good method in todays homes but was acceptable back than. Homes in that era where not well insulated nor sealed as todays homes.

Back than ('47) drafts in homes abound, so intakes where basically not needed nor likely thought of as needed. Not so today. Intakes for fresh air are now required in many codes.

Dual wall vented appliances, such as the water heater do not need fresh air intake(s). The fresh air for combustion is drawn in through the dual walled vent and the exhaust is removed throught the same vent.

Regarding the furnace, the Tjernlund system may or may not need an extended flue vent above the roof line. Codes locally will dictate that. Power venting may not even be needed.

May cause more harm than benefit. Lower efficiency by drawing out more combustion air from within the furnaces firebox than furnace is designed to have and reduce efficiency.

Best bet is to contact furnace maker and consult with them prior to installing any additional power venting device, unless codes clearly state one is required.

Check the codes for fresh air intake into the area where furnace is. Todays codes require fresh air intake vents for non dual walled venting appliances. About all I can provide you with in the line of help with that furnace.
 
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