Hearth and Forehearth Height Difference

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TXDS76901

New Member
May 2, 2022
6
San Angelo, Texas
I have a 1928 masonry wood-burning fireplace that sits at floor level. We would like to raise the level of the firebox floor (hearth) and the forehearth to about 8" in height for a much more modern look. We are going to be converting to vented gas with concrete logs, etc. We would like the fireplace to be able to still burn wood should a future homeowner decide they want to go that route. My question is ... how much lower can the firebox floor be than the forehearth? We like the look of the firebrick lining in the firebox so we are not interested much in an insert. It would seem that raising the firebox a couple of inches less than the concrete non-combustible forehearth would not make much of a difference. Any thoughts or experience with this type of situation would be most appreciated.
 

begreen

Mooderator
Staff member
Nov 18, 2005
93,171
South Puget Sound, WA
What would the finished opening height be with these changes? A 6-8" reduction in the fireplace opening height could affect future homeowners if they wanted to install an insert and the current opening is not very tall.
 

EatenByLimestone

Minister of Fire
Isn't chimney area calculated off fireplace opening size? Could altering the fireplace that much affect how well it drafts?
 

TXDS76901

New Member
May 2, 2022
6
San Angelo, Texas
What would the finished opening height be with these changes? A 6-8" reduction in the fireplace opening height could affect future homeowners if they wanted to install an insert and the current opening is not very tall.
The existing fireplace was presumably built in 1928 when the original house was built. The prior owner did a substantial amount of demolition work removing all interior sheetrock, electrical, plumbing, etc. Evidently, as you can see in the attached picture, a substantial amount of brick was also removed during the demolition. The mason I am working with does not believe there was ever a damper installed on the original fireplace. This is a problem since we are wanting to control (or minimize) any air infiltration so we have secured a cast iron replacement damper from Vestal to be installed by the mason as well as some steel lintels. In looking up through the chimney, there is absolutely zero evidence of soot. There is a double chimney above the smoke shelf. Attached is a picture of our objective for this fireplace. We want to raise the forehearth a minimum of 6" and a maximum of 8". Since the firebox floor and hearth are currently the same height, we will need to raise the firebox height appropriately. In looking at inserts, we could not readily find an available one that would fit in the fireplace box, albeit our search was last year, and supplies may have changed. I believe our opening after modifications will be 24" x 33", or 22" x 33" depending on high we raise the forehearth. Thanks in advance for any comments, suggestions, or answers.

Fireplace Dimensions.jpg Fireplace Picture - Current.jpg Fireplace Picture - Objective.jpg
 

Ashful

Minister of Fire
Mar 7, 2012
16,358
Philadelphia
Do what makes you happy, but that objective photo would look a lot better if it were not a raised hearth, but rather flush to the floor.

Chimney cross-sectional requirement is indeed calculated on opening, with the usual problem being too little chimney cross section for a given opening. There's some range in the recommendations, so it's entirely possible the opening could be reduced without requiring a completely new chimney.

Anything you do now can be undone, it's only a question of effort and cost. The fireplace behind me had an original opening of 30 square feet, reduced about 120 years ago to something less than 15 sq. ft., then framed in and converted to a gas insert in the 1990's, before being fully gutted by me and opened back up to it's 1775 configuration. Anything is possible, so unless you're concerned with preserving historic construction, I'd not let potential future owners' desires influence your decision.
 

TXDS76901

New Member
May 2, 2022
6
San Angelo, Texas
Do what makes you happy, but that objective photo would look a lot better if it were not a raised hearth, but rather flush to the floor.

Chimney cross-sectional requirement is indeed calculated on opening, with the usual problem being too little chimney cross section for a given opening. There's some range in the recommendations, so it's entirely possible the opening could be reduced without requiring a completely new chimney.

Anything you do now can be undone, it's only a question of effort and cost. The fireplace behind me had an original opening of 30 square feet, reduced about 120 years ago to something less than 15 sq. ft., then framed in and converted to a gas insert in the 1990's, before being fully gutted by me and opened back up to it's 1775 configuration. Anything is possible, so unless you're concerned with preserving historic construction, I'd not let potential future owners' desires influence your decision.
Thank you very much for your feedback. We live in an area in Texas that does not have very many days/nights that a fireplace gets used. It's always a difficult decision on what changes to make. Is it possible to raise the firebox floor using cut stone rather than firebrick? It would certainly make it easier for a future conversion back to the original masonry fireplace. Also, if my forehearth is 2 inches taller than the firebox, I am thinking that would not be an issue? Would you agree or should I try to maintain the same level?
 

EbS-P

Minister of Fire
Jan 19, 2019
2,415
SE North Carolina
Have you considered a zero clearance fireplace install and demoing all the masonry that needs to go?

What is supporting the hearth now? Do you have a basement?
 

TXDS76901

New Member
May 2, 2022
6
San Angelo, Texas
Have you considered a zero clearance fireplace install and demoing all the masonry that needs to go?

What is supporting the hearth now? Do you have a basement?

The hearth (firebox) is supported by a concrete foundation underneath. There is no ashpit. There is no basement. The forehearth is concrete that appears to have been colored and cut to look like tile. I am unsure how thick it is.

In looking at inserts, I found it difficult to find one that would fit. The back of the existing masonry firebox starts to slant forward after only 10 inches. Most inserts I looked at were rectangular.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,415
SE North Carolina

TXDS76901

New Member
May 2, 2022
6
San Angelo, Texas
The picture you showed looked like averageish depth and slant. How about a Blaze King princess insert. It’s shallow. So it really sounds like you have lots of options. With the concrete slab under it all

View attachment 295366

Thank you for your reply. Allow this is not quite the look we are attempting to achieve, but it does show that there are options. In looking at the manual and dimensions, it appears that I would have to position the insert quite a bit forward (away from the back of the current back of the hearth) in order to properly vent the insert through the chimney and clear the smoke shelf. This is counterproductive for our application as we are trying to work with the current footprint of the hearth and not extend the forehearth any further into the room while raising the level of the firebox floor... which pushes the insert further into the room.