I did a quick math on my Furnace. Even when adding the air exchange vents, the air return is not even close to the same as what is fed in the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for efficiency?
Furnace is a late 1980 wood/electric Newmac.

cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange
vents, the air return is not even close to the same as what is fed in
the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for
efficiency?
Furnace is a late 1980 wood/electric Newmac.

Return air surface area should be like 125% of total output surface area -
more if the return path is long .
--
Snag

Return air surface area should be like 125% of total output surface area -
more if the return path is long .
^^thanks Terry

Wow, I'm surprised my ducting hasn't buckled! I will add some returns in the basement since there's only 1 for the Air Exchange (4"). The kids bedrooms are also a bit cold so I might add some returns there as the hallway air return doesn't seem to be enough.


(found my scrap paper; Rough measurement is 527sq hot air supply and 331sq for return)

On Tuesday, December 6, 2016 at 8:17:17 AM UTC-5, cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange vents, the air return is not even close to the same as what is fed in the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for efficiency?
Furnace is a late 1980 wood/electric Newmac.

IDK that it's a simple as that, ie that the intake area should equal
the output. There are more outputs because the heat/cooling needs to
be delivered to certain areas, while the return air intake locations
can be fewer and are not as critical. To deliver air to all those
places requires at least minium size ducts and registers. So, I would
not be surprised that the outputs would add up to more than the intake.
If there is some guideline, I've never heard it. The important thing
is that there is sufficient duct capacity for the blower size. If
you meet that on the intake and output, not sure that it makes a lot
of difference if you have extra outputs. Whether you meet it or not
can be determined by calculation or measured by pressure drop.

On 12/6/2016 8:39 AM, trader_4 wrote:
On Tuesday, December 6, 2016 at 8:17:17 AM UTC-5, cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange vents, the air return is not even close to the same as what is fed in the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for efficiency?
Furnace is a late 1980 wood/electric Newmac.

IDK that it's a simple as that, ie that the intake area should equal
the output. There are more outputs because the heat/cooling needs to
be delivered to certain areas, while the return air intake locations
can be fewer and are not as critical. To deliver air to all those
places requires at least minium size ducts and registers. So, I would
not be surprised that the outputs would add up to more than the intake.
If there is some guideline, I've never heard it. The important thing
is that there is sufficient duct capacity for the blower size. If
you meet that on the intake and output, not sure that it makes a lot
of difference if you have extra outputs. Whether you meet it or not
can be determined by calculation or measured by pressure drop.




http://www.johnrwhite.net/three%20st...t%20sizing.htm

On Tuesday, December 6, 2016 at 9:08:46 AM UTC-5, cln wrote:
Return air surface area should be like 125% of total output surface area -
more if the return path is long .
^^thanks Terry

Wow, I'm surprised my ducting hasn't buckled! I will add some returns in the basement since there's only 1 for the Air Exchange (4"). The kids bedrooms are also a bit cold so I might add some returns there as the hallway air return doesn't seem to be enough.



What kind of basement? Finished or un?

AFAIK they don't usually put returns in an unfinished basement due to dust
and typically colder air. (I could be wrong, but that was my understanding.)

AFAIK they don't usually put returns in an unfinished basement due to dust
and typically colder air. (I could be wrong, but that was my understanding.)

Our plan is to finish the basement, but valid point.



[Taxed and Spent , thank for the link]

On Tuesday, December 6, 2016 at 1:24:30 PM UTC-5, cln wrote:
AFAIK they don't usually put returns in an unfinished basement due to dust
and typically colder air. (I could be wrong, but that was my understanding.)

Our plan is to finish the basement, but valid point.



IIRC there is also some rule about the return not being placed in line of
sight of gas burning equipment, e.g. furnace, boiler, WH, etc.

If you finish the basement and build a utility closet, there should not
be a return in that closet.

There are quite a few HVAC's forums that you could browse for more info.
Just be sure that the info is up to date. Some forum posts might be
outdated with regard to "what was standard at that time" and also code.

On 12/6/2016 8:17 AM, cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange vents, the air return is not even close to the same as what is fed in the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for efficiency?
Furnace is a late 1980 wood/electric Newmac.


One way to balance the heat around the house is to partly close the
vents in some rooms while keeping the others wide open. Doing that, the
ratio just changed.

What is important is having enough opening both in and out to handle the
capacity of the blower so it is not restricted.

As for replacing a 36 year old furnace, good chance you will save money
over time. You'd have to do some comparisons to see if it makes sense.
My oil fired boiler was in need of repair and possible replacement so
upgrading was an easy decision. Payback is about 7 years for me.

On Tue, 6 Dec 2016 07:42:53 -0600, "Terry Coombs"
wrote:

cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange
vents, the air return is not even close to the same as what is fed in
the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for
efficiency?
Furnace is a late 1980 wood/electric Newmac.

Return air surface area should be like 125% of total output surface area -
more if the return path is long .
I've always worked with the goal of 150%

On Tue, 6 Dec 2016 15:55:23 -0500, Ed Pawlowski wrote:

On 12/6/2016 8:17 AM, cln wrote:
I did a quick math on my Furnace. Even when adding the air exchange vents, the air return is not even close to the same as what is fed in the floor vents and such. if I'm generous it may be 3:2 ~ out:return

I'd also like your opinion on if this should be replaced for efficiency?
Furnace is a late 1980 wood/electric Newmac.


One way to balance the heat around the house is to partly close the
vents in some rooms while keeping the others wide open. Doing that, the
ratio just changed.

What is important is having enough opening both in and out to handle the
capacity of the blower so it is not restricted.

As for replacing a 36 year old furnace, good chance you will save money
over time. You'd have to do some comparisons to see if it makes sense.
My oil fired boiler was in need of repair and possible replacement so
upgrading was an easy decision. Payback is about 7 years for me.
There is a good chance your newmac is oversized for your
application, but if you are burning wood the efficiency is not as much
of a "killer" as if you are using electricity - and even thern it
depends where you are and what you pay for electricity. Here in
Ontario you don't want to be heating with electricity if there is ANY
option. Burning $5 bills would be about the only way to heat that
would cost more than electricity here.

One way to balance the heat around the house is to partly close the
vents in some rooms while keeping the others wide open. Doing that, the

All vents are fully open except the 'too hot master bathroom'.

What is important is having enough opening both in and out to handle the
capacity of the blower so it is not restricted.

I should call in a professional...............again

As for replacing a 36 year old furnace, good chance you will save money
over time. You'd have to do some comparisons to see if it makes sense.
My oil fired boiler was in need of repair and possible replacement so
upgrading was an easy decision. Payback is about 7 years for me.

We just installed a ductless heat pump, this will be our first winter with it so I'll play it by ear. It also came in handy having it on hooked on the generator panel last week when the power was out.

I think at this point, investing in more attic insulation and improving other cold spots (bay area) would be a better investment.


There is a good chance your newmac is oversized for your
application, but if you are burning wood the efficiency is not as much
of a "killer" as if you are using electricity - and even then it

Good point. also, if it ain't broken...

On Tuesday, December 6, 2016 at 1:24:30 PM UTC-5, cln wrote:
AFAIK they don't usually put returns in an unfinished basement due to dust
and typically colder air. (I could be wrong, but that was my understanding.)

Our plan is to finish the basement, but valid point.



[Taxed and Spent , thank for the link]

Well, until it's finished and used, you don't want to be putting
returns down there. Even worse, with a return and no outlets in
an unfinished basement, it will pull air from outside, interfere
with any gas water heater venting, furnace venting, etc.