I would like to know how much capacity a 4 , a 5 , a 6 or a 7 inch flue liner can handle. Currently I have 191k btu of furnace 80% and a 40k btu water heater being handled by an unlined mostly internal chimney. Had to tuckpoint the chimney after 17 years of this altho the cracked cap may be the cause of this. If I get a two stage furnace I am concerned that i will get more condensation at low fire.
Reline the chimney with the size dicated by the National Fuel Gas code.
You have 191% btuh 80% gas furnace?
I have a 71k 80% and a 119k 80% furnace. I don't have a copy of the guide and want to be sure that when I replace the furnace that the correct liner will be placed by the contractor. The size of the replacement units has not been determined and the I may increase the size of the water heater in the future.
Will there be more condensation at low fire?
No, the two stage furnaces are generally treated the same as the single stage ones. In fact for 80% furnaces, the venting instructions provided by the mfg are generally pretty limited since they dont have jurisdiction. They tell you the vent size for their equipment and that data needs to be checked against the others and the NFG regulations.
You'll need to wait till you know the sizes of ALL appliances that are being vented, to determine the correct size, plus the heigth of the chimney.
When your having the work done, and the contractor tells you what size liner, post back with all the info, and then we can douoble check for you.
Here my info
Chimney is 27 ft 5 inches tall from the base at he basement floor to the top of the flue. It has a round flue that is 7 3/4 in. inside diam. There is a 10 inch square flue for the fireplace. Chimney is mostly inside. 3 sides are inside the house for the first 21 feet and the 4th side is in the house for the first 16 feet then there is 5 ft of attic. The two furnaces the contractor will install are 80%, 120k and 40k input and I have a water heater that is 40k but I probably will replace it with a 50k unit.
Contractor says that he can only line with a 6 inch liner that would be too small for the output. He suggests we go without lining the chimney. 90% furnace is an option but there are potential venting problems. I did have the 40k water heater, and two 80 % 119k and a 71 k furnace run thru the chimney for about 21-22 years, Replaced chimney cap about 10 years ago and needed tuckpointing 5 years ago.Tuckpointing is still solid.
What size liner do I need for a 50k water heater and the 120k and 40k furnaces. Does the mostly inside chimney prevent condensation? Will a two stage furnace lead to more condensation at low fire? Do you think my chimney will survive?
A 6" liner using b vent from the appliances with handle 204,000 at 20', and 221,000 at 25'.
The chimney is measured from the top of the appliance to the top of the chimney.
So use the 20' rating.
So 6" should handle your planned set up.
A 2 stage will condensate more in first stage, because your chimney won't warm up as quick.
I made a mistake on my measurement. I remeasured and the chimney measures 22' 4" from the top of the furnace to the top of the flue. Furnace is 4 ft tall. Chimney is one foot shorter than if I used the original measurement. Using your data and interpolating half way between 20 ft and 25 ft I should be at the border of the capacity of the 6 inch liner. Half way between 221k and 204 k is 212.5. The total btu's of my appliances is 120+40+50=210 Is this legitimate to do?
I assume a chimney cap makes no difference since there appears to be lots of free space around the cap.
Just wondering why a taller chimney allows more heat to go up it, I would seem that there would be more resistance to flow. Is it that there is more wind to pull the fumes up high? Is this why factories have tall chimneys?
What is b vent?
Is this data published somewhere that can be assessed so I can show the contractor?
The higher the chimney, the greater the draft created.
Your contractor can get all the info he needs from his liner supplier, thats where we get ours.
You shouldn't push it to the max, should have a little safety in the size.