Oil Furnace blower Q


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Old 06-25-11, 11:51 AM
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Oil Furnace blower Q

Hi
I would like to know the CFM capacity of my[ 80.000 btu] oil furnace blower,dont know if this info is display some where .I did check but couldn't find it.
Motor is 1/3 HP 1750 rpm , pulley ratio about 1- 2
Thanks for help
 
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Old 06-25-11, 01:34 PM
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We would also need to know the length and diameter of the blower wheel. Even then it would be a guess but a fairly close guess.

This sounds like a fairly old furnace, belt drive blowers haven't been used for in the last twenty years that I know of, maybe longer.
 
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Old 06-26-11, 05:28 PM
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Thank you Furd
The furnace was installed in 95' and Im replacing it with a gas furnace.One question I have is if I should expend $1500 extra getting a furnace with a variable speed blower or save the $ and go single stage
I would like to know the CFM of the oil furnace blower to compare with the gas furnaces to see if I can expect an improved air flow in some of the rooms upstairs
furthest from the furnace
I measure the oil furnace blower, the casing is 16'' diameter and 13'' wide, the wheel about 14'' diam. and 11'' wide.It probabely turns at half the speed of the motor
[1750 RPM] around 900 RPM
Rodel
 
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Old 06-26-11, 08:58 PM
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Unless you are really needing the airflow on your present furnace I am going to not look it up right now.

For the extra $1500 you should be getting a two-stage burner AND the variable speed blower. I strongly recommend both options and I'll explain why a bit later.

If you are having an airflow problem with your heating system it is a DUCT issue, not a furnace or blower issue. Increasing the airflow might increase the heat to the problem room(s) but it definitely will cause noise problems everywhere. It will likely cause the furnace heat exchanger to run colder than it is engineered and that could cause premature failure just as much as it running too hot.

The standard blower in a forced air furnace has either three or four speeds that can be selected at the time of installation. Variable speed blowers have many more discrete speeds and so are better able to be adjusted for the duct deficiencies AND to maintain the proper heat exchanger temperatures. If you also have cooling with the same ductwork and blower the cooling will also benefit. The variable speed blower motors are significantly more energy efficient than are the three or four speed motors and this means that you can leave the variable speed blower running constantly for minimal expense in electricity. Constant blower operation will do wonders to even out the temperature differences experienced with deficient ductwork. When set for constant operation the blower runs quite slowly and the noise level is correspondingly quite low, usually inaudible.

The two-stage burner is also a comfort item. The furnace needs to be just big enough to keep the house warm during the coldest weather. That means that something like 90% of the time the furnace is really too large. Two-stage burners operate on the first stage only unless the inside temperature is so cold that it simply cannot make any headway. This means that your furnace will run a bit longer but burn no more fuel while keeping the house far more comfortable. It also makes sizing of the furnace a bit less critical. Remember, almost all original furnaces are way oversize for the house and if you have made any energy saving improvements like insulation, weatherstripping, new windows or doors or the like it is almost guaranteed that your furnace is way oversized.

You will save some fuel with the two-stage burner and variable speed blower and you will save significant fuel if your old furnace was vastly oversized. While the extra cost won't be recovered in the first couple of years of operation the comfort level in the house will be much appreciated.
 
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Old 06-27-11, 04:28 PM
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Furd thank you very much for your perspective , if you reading this

The house is 75 yrs old with basement and two floors, in the 60's the original furnace [gravity ] was replace with forced air [oil] and two new ducts [ round 5''] added in the basement to the original fife round 6'' for the rest of the house.
There are two air returns in the main floor and one at the bottom of the entrance stairs.No returns in the top floor.

In 2004 due to an asbestos problem most of the ducts were removed and replace with new round 6'' and two wall stacks 10'' x 3 1/4'' for the three bedrooms and bath upstairs keeping the same lay out . The old 12''x 10'' side wall grills replaced
with 4''x 10'' grills to match the new boots. Unable to run new ducts under the floors upstairs to install floor outlets
The retrofit was very dificult soI had to partialy open some walls and ceilings
Two round 6'' were conected to the two wall stacks, one finishing bellow a wall common to the bath and one bedroom, supplies those two

The top of the other stack is right under another wall of a small bedroom so to suply was easy, but to reach the MB a 3 foot piece horizontal was needed and absolutelly no room to install a T or something else.
The only thing I was able to do was to cut a hole on the stack about 12'' bellow the end where the outlet for the small room is, and install a 6'' round takeoff for the MB to share the suply with the small bedroom.

The problem with that is that is very difficult to balance the air flow between these two rooms. The grill in the small bedroom has to be almost close to get a good suply in the MB.
It works like a valve closing the top of the stack and allowing the pressure to increase and divert air trough the takeoff and round 6'' to the MB

In general the air flow through the house is much better than before, the problem area is getting enough suply for the MB and the smaller bedroom at the same time hence my question about the blower.
Im selling the house and Im traying to solve a problem the best I can for the future owner,however when purchasing an old house some of this is expected and since $ is in short suply Ineed to consider very carefully what furnace to buy
THANKS AGAIN
 
 

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