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Can I bump out a fireplace like this?

Posted by nealwin (My Page) on
Mon, Sep 24, 07 at 17:24


OK, this is the famous fireplace cross section with a gas insert (courtesy of Mendota) ...

I want to bump out the insert in the room to accomodate some built in cabinets on the fireplace flanks like this ...

Simple box out of 2x4's and plywood envisioned.

Fireplace guy said "no" .. but seems do-able to me as long as I make sure there is enough room to bend the ductwork.

My existing masonry firebox is 44" wide and 28" tall, and many inserts are 20" tall or so and seems like plenty of room to maneuver.

Am I crazy?

Follow-Up Postings:

RE: Can I bump out a fireplace like this?

As drawn, I think the bend from the top of the insert to the existing chimney is too severe.

Maybe you could use a 'regular' insert that vents out the back of the firebox, then go up with it.

And you should take a flashlight, and look at the inside of your specific FP: your vent may be somewhat different than pictured.

RE: Can I bump out a fireplace like this?

In addition to the bend in the flue which may be excessive, I'd be concerned about framing around the box - what's the rated clearance around the firebox? Also, code requires a non-combustible hearth in front of the firebox opening - so you would have to extend that out (usually at least 12 inches and sometimes more).

RE: Can I bump out a fireplace like this?

Should be able to, but...

First, read the Insert Manual. If you don't have it, find the model and manufacturer on the rating plate (should be on the base near the valve). Go to the manufacturer's website and download it for free.

Second, pull the unit out and see what kind of room you have to play with your Damper opening. Some are a bit larger than others and will allow to bring the venting closer to the front. If you've never pulled your insert out, there should be a plate atop the unit which the two flex lines are attached. Carefully slide that back as you pull the unit forward (should be some sort of handle pushed in at the top you will need to pull out, reattach and slide back - refer to manual). Oh, and make sure the gas line is disconnected.

If you do have the room, all your framing clearances (clearances to combustables) will be stated in the Manual. Or use metal studs and cement board. If it is going to be tight on the venting and you run a risk of pinching the vent, I recommend you do not attempt it. Should be plenty of play with the 8" you say you have. Venting is most likely a 3" flex. Keep in mind that Inserts are designed to vent vertically, not horizontally. Any long horizontal run and you may loose some of your draft which may cause problems with the burn. The other thing you could do, as Oruboris had stated, is purchasing a new "built-in" fireplace and run a flex line from that up your existing flue. In that case you will probably be bumping out more than 12" though.

RE: Can I bump out a fireplace like this?

the mendota d40 and d30 both use 4"vent and intake. i have seen it done before but in a very large fireplace

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