Fireplace heatloss calc

Rodney Summers

We have a wood burning fireplace in our SE facing living room. The 2-story chimney is located on an exterior east-facing wall on the first floor. There are heated rooms both above and below the LR and it has a total of 38 feet of exterior walls. The house is stucco and has what looks like 1/2" or so rolled burlap/wool/??? tacked between the studs.



The firebox is 39"w x 31"h x 21"d. We do have an old-style damper currently, but will be replacing with a chimney-top mounted stainless damper which actually seals when closed.



We live in Minnesota and use the fireplace 2 or 3 times per week during the heating months.



How can I go about calculating the heatloss of this room including the fireplace? In other words, what sort of impact does the fireplace have on the overall heatloss of the room?



There are 2 radiators in the LR right now. They are EACH 5-column, 33 sections and 20" tall. There is heated space both above and below.



Room dimensions are 25ft x 13ft. There are 47.85sf of old-style double hungs with wooden/original storms. There is also a set of french doors (also with wooden storms) that total of 27sf.



Without chaning the radiators, how do I determine the designed mix water temp for the zone supplying these radiators?



Thanks again and sorry for the long-winded post.

A.J.

Fireplace will definaltly

> We have a wood burning fireplace in our SE facing

> living room. The 2-story chimney is located on

> an exterior east-facing wall on the first floor.

> There are heated rooms both above and below the

> LR and it has a total of 38 feet of exterior

> walls. The house is stucco and has what looks

> like 1/2" or so rolled burlap/wool/??? tacked

> between the studs._br__br_

>

> The firebox is 39"w

> x 31"h x 21"d. We do have an old-style damper

> currently, but will be replacing with a

> chimney-top mounted stainless damper which

> actually seals when closed._br__br_

>

> We live in

> Minnesota and use the fireplace 2 or 3 times per

> week during the heating months._br__br_

>

> How

> can I go about calculating the heatloss of this

> room including the fireplace? In other words,

> what sort of impact does the fireplace have on

> the overall heatloss of the

> room?_br__br_

>

> There are 2 radiators in the LR

> right now. They are EACH 5-column, 33 sections

> and 20" tall. There is heated space both above

> and below._br__br_

>

> Room dimensions are 25ft x

> 13ft. There are 47.85sf of old-style double

> hungs with wooden/original storms. There is also

> a set of french doors (also with wooden storms)

> that total of 27sf._br__br_

>

> Without chaning

> the radiators, how do I determine the designed

> mix water temp for the zone supplying these

> radiators?_br__br_

>

> Thanks again and sorry for

> the long-winded post.

A.J.

Fireplace will definitly increase your infiltration

but if your going to put a new damper in I wouldn't loose any sleep over your room being cold.
I don't understand why you want to mix your water going to the radiator. If you have a two pipe system with radiators heating your house I would be more concerned with boiler condesation.

Kupetz's Plb & Htg

Constantin

There cannot be an exact answer...

... without a blower-door test. The biggest culprit with chimney's is the heat loss via the flue. For my climate, the ACCA Manual-J results vary by a factor of 6, depending on the "quality" of the fireplace. BTW, I put Lymance dampers on the tops of my chimney caps and the blower-door guy that came to our house was impressed how tightly insulated it was.

Making some assumptions (like 9' ceilings), I slapped the data you gave into HVAC-Calc to come up with the following heat loss calculation for a design day in Duluth, MN (-10°F) - see below. They come with no guarantees, as I'm a mere homeowner, not a heating technician.

Note the very low chimney losses. This is due to the fact that the floor area is very small (only one room). Were I to input the sq ft. floor area of your entire home, the results would scale by some factor set by Manual-J.

Extrapolating, it is not inconceivable that your heat loss on a design day may be around 14kBTU/hr for that room alone. The only way to know is to run a Manual-J compliant heat loss calculation for the whole house.

I would look up the capacity of the radiators to determine the supply temperature needed to keep you happy on a design day. That information should be available from the manufacturer or you may be able to find it in the Library (see toolbar at left).

hr

Some of those

insert type wood burners had combustion air ducted to, or near, them. This would be a big source of heat loss. certianly would not want to cap them off if wood will be burned in the unit, however.

hot rod

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jeff_51

that is an uninsulated exterior masonry wall

the slant fin heat loss calc you can get here for free has a design criterium (can't spell) in it that will help. Call us at651-426-6404 and ask for Randy. Tell him Jeff told you to call and I think he can give you a pretty good answer. We are in the twin cities. Measure up the square footage of exposed brick face. I usually figure a door area and figure it with no insulation. That may be a bit too much, but should get you close in this area

Jimmy Gillies

Heatloss with a open fire

Chris,
I was always told that if you have a fire in any room it would increase the number of air changes to say 21/2-3 each hour.
I have used this method while doing heatloss calcs for a number of years.
I hope that helps?
Kind regards.
Jimmy Gillies (Scotland)