Old Heatilator Fireplace Retrofit

[TomSeller]

One of my houses has an older Heatilator fireplace that I want to retrofit with a high efficiency insert and a new SS liner up the masonry chimney to the roof. The fireplace is in the center of the house with the two heat pump forced air returns on each side about 15' away. So running the blower with the insert in use makes sense to get the heat distributed through the house. I'd like the masonry mass (large as you can see) to store heat but it seems all the inserts these days only vent to the room. There are two vents into the crawlspace for combustion air, but the inserts that I have seen are not set up to take in outside air and use room air. Any ideas on what you would do?

 

[TomSeller]

Bump..

 

[Egon]

Outside air to very near the combustion inlet. Ducting to come off of insert hot air outlet to the Masonary.

 

[RNeumann]

I doubt the insert is taking combustion air from the room. Most would use the outer "chimney" for intake and the middle for exhaust. With regards to the mass- you will need to allow the warm recirculating air (fan on insert) to heat that mass. Their is no venting of combustion air into the room and the chimney and outside firebox cover (exterior of insert) aren't that warm.
Bottom line is the inserts are designed to work as is. You trying to reengineer and overthink things ain't gunna work like you want or think it should. Plus a thermal mass doesn't need to be heated from the inside out.......

 

[TomSeller]

Outside air to very near the combustion inlet. Ducting to come off of insert hot air outlet to the Masonary.

So in my case where the crawlspace air comes into the sides of the existing fire box, you would fabricate a duct that routes the crawlspace air beside the new insert up to near the insert's combustion inlet?

 

[TomSeller]

I doubt the insert is taking combustion air from the room. Most would use the outer "chimney" for intake and the middle for exhaust. ...

I thought the inserts used room air for combustion like a typical wood stove. If they use combustion air from the outer chimney, that would be ideal. I've never had an insert.

 

[RNeumann]

I assume the insert has a sealed front door? When I hear insert I think wood burning stove that is made to be inserted/retrofitted into an existing open wood burning firebox. It will make a huge difference and once warm the rock will help hold heat and make the place comfortable. It will be a nice addition! Good luck and enjoy the project.

 

[RNeumann]

So in my case where the crawlspace air comes into the sides of the existing fire box, you would fabricate a duct that routes the crawlspace air beside the new insert up to near the insert's combustion inlet?

The new unit is sealed and probably won't use anything from the crawlspace. If the insert doesn't take combustion air from the chimney then it will have a 4" inlet in the back or side of the unit. This is the same size a dryer duct. If that is the case you could duct that down into your VENTED crawl space.

They circulate air around the firebox (between the firebox and outer metal skin) with a little recirculating fan.

A third combustion air option (and something I haven't seen) is taking combustion air from the room. Note that is what they do with the install below.
How to Install a Wood-Burning Fireplace Insert - This Old House - YouTube

 

[teejk]

I thought the inserts used room air for combustion like a typical wood stove. If they use combustion air from the outer chimney, that would be ideal. I've never had an insert.

Can you find an insert small enough to fit the existing firebox? My MIL wanted to do something similar to what you have but nobody could help her.

 

[TomSeller]

Can you find an insert small enough to fit the existing firebox? My MIL wanted to do something similar to what you have but nobody could help her.

It is a fairly large fireplace, the ones at the local wood stove place looked like they would fit but I need to get to measuring.