Suggestions on how to make a Heat source from fireplace

We purchased a 1940s house in Minnesota 6 years ago. In the a 1980s they build a room adjacent to the fireplace so they knocked out the back of the fireplace so that it was open to both rooms.  At some point that also piped gas to it so there can be a decorative flame if we want to light it.  I love that you can see between rooms through it, but here is the problem.  

What we didn’t know when we purchased the home was that the add on does not receive enough air from the central air to heat the room even though there are two vents in there. There is also an electric baseboard heat. With both running, that room is still too cold to use in the winter so every winter we close up that room and put insulation on both sides of the fireplace and wait for spring. We can’t use that room for 4-6 months every year. The worst part is it is our favorite room and one of the main reasons we purchased the house so we are bound and determined to use this room this year.

We just can’t figure out how to heat it.  Every time we come up with an idea we get a quote for 10k. This is not our forever home so we don’t want to dump a ton of money into being able to heat this one room.

I was hoping we could put a wood stove in the fireplace but every time in inquire about it they want to put in an insert and close off the other side, or they want to put a wood stove on one side and run a pipe out the back up the chimney.  That wouldn’t be very attractive from the other side so I’m not sure what the point is. It seems like there should be a wood stove small enough to fit in the fireplace that would provide heat to both rooms.

We are open to to sealing off the fireplace and using a different heat source, but I have no clue how to seal off the fireplace and haven’t been able to find anything online that explains how to do it.  

Am also not sure what we would use. Everything seems to be ridiculously priced to install. We already have solar on our south facing roof so I don’t think solar heat is an option.

You all have such great ideas so am hoping someone has a creative solution that will work for us.  We do live in the city so Rocket mass heaters aren’t an option. Wouldn’t be able to get a permit to do it.

Is this what you're hoping for: https://www.acucraft.com/product/see-through-fireplaces/

Or one of these: https://duckduckgo.com/?q=see-through+woodstove&t=h_&iax=images&ia=images

Mary Osterburn wrote:

What we didn’t know when we purchased the home was that the add on does not receive enough air from the central air to heat the room even though there are two vents in there.  

Let's hear more about how you've trouble shot this one.
1. do the pipes come through an un-insulated area like a crawl space and if so, can you access them to add a bunch of insulation around them so that the air is still warm when it gets there?
2. are there a bunch of necessary or unnecessary bends in the pipes that are slowing the air flow?
3. are the pipes too small, so it's dividing the flow - do you get better flow if you actually close one?

And wrote:

There is also an electric baseboard heat.

Again - how is this working? We have some of that and it requires both sides of a paired breaker for 220 volts (I'm in Canada but I think the rules are about the same). We have one in our back well-shed, but only 110 volts are available so it puts out barely enough heat to stop pipes from freezing for a normal year - if it looks like atypically cold like two weeks of snow - we have to drain the whole system.

And wrote:

In the a 1980s they built a room

Who built? Did anyone inspect it? Built to what standards? Is it insulated? Insulated properly? Does it have too many windows so you're loosing all your heat that way? Is it on the north-west side so it's got too much wind-chill? Is it on an uninsulated slab which is leaking all it's heat to the ground? Is the ceiling properly insulated?

Sorry to bombard you with questions, but if the room's too cold despite heating it 3 ways, I'd be looking at where all that heat is leaking out or migrating to. If they owners failed to make sure it was properly sealed and insulated, not much is going to help you short of identifying where the heat is going and doing the work to fix the problem. Adding extra insulation to an attic area is fairly easy - but protect your lungs! Insulating some of the windows with multi-layer wool shades could help if you are willing to reduce the window square-footage. If wind-chill is the problem, look outside for ways you can re-direct or slow the wind with hedges, fences or even a stack of firewood.

And wrote:

We are open to to sealing off the fireplace and using a different heat source, but I have no clue how to seal off the fireplace and haven’t been able to find anything online that explains how to do it.

I don't see how sealing it is going to help you?  

We heat mostly with a wood stove on our lower level and its number one issue is the uninsulated slab. However, there's enough thermal mass there that since we've got plenty of wood to burn, we just put up with it. If things get really cold, I finally talked Hubby into an insert in the upper level fireplace. Yes - very pricey - but it sure warms up the place! However there's not a lot of thermal mass upstairs, so it only helps while it's burning. The original owners put 2 sliding patio doors on the north side of the upper floor with metal frames. In a heart beat, I'd replace them with a single door with an opening window beside it. In the short term, they at least got warm draperies over them! There are plenty of simple drapes that aren't hard to sew if you're up to learning a new skill or already have the skill.

I’m not sure who built the room, but it was inspected per the property records so I’m sure it was built to the standards at the time. It certainly has more insulation than the rest of the house as I don’t think there is any insulation in the walls in the original portion of the home.  It does have a lot of Windows.  The east side has a huge picture window taking up half the wall.  The west side has french doors taking up a big chunk of the wall and a large picture window above it. It doesn’t have an attic. Rather it has vaulted ceilings so not sure how much insulation is between the ceiling and the roof. I’m guessing not much.

However, despite all that, I still think it probably holds more heat than the rest of our house. We had a blower door test done the first winter we were in it and it was off the charts leaky.  We spent 10k for someone to seal leaks and add insulation to the attic and rim joists and it did almost nothing. The results barely changed afterwards.  Sooo the house apparently has issues.


The add on does have a crawl space under it.  I say crawl space, but it is only a couple of feet high and there is no way to access it.  The only hole into it is where the HVAC pipes pierce the foundation in the basement to get to it.  

Not sure what the issue is with the ductwork.  It is old 1940s ductwork and is kind of crazy.  There are bends everywhere because I’m certain the house originally used to have a boiler so the duct work was added later.  I’m pretty sure the ductwork was done really well when it was first put in because one HVAC person who came out to look mentioned that there was no way anyone would be able to afford the ductwork as it was designed today. I have had at least 5 HVAC companies come in to trouble shoot it and no one has been able to figure out what the problem is.   It does however have a bunch of holes punched in it because someone in their wisdom decided that running phone lines through the duct work was a good way to get phones service through the house.  Funny since no one has phone lines anymore.  I’ve patched some of those but it really needs more work.  The cold air returns run through the joists and I know the cold air returns are part of the problem. Would love to learn how to convert them to a better system.  Some of them are no longer connected to the furnace because of remodeling by former owners and I’m not sure how to reconnect them since there are now wood beams blocking the path.  This add on is one of those rooms.  Our house is very out of balance.  When the heat is running you can feel a draft of air flowing into the basement.  If I leave the basement door open, it will shut on its own when the heat kicks in.  Not good

The heat coming out of the vents wouldn’t be enough to heat any room.  You can’t even feel the air coming out- I can see the higher temp with a thermal camera, but it just doesn’t flow.  Have no clue how to fix that.  


I don’t know anything about the electric baseboard.  We only tried it the first year we lived here. Haven’t turned it on since.

@Michael.  Thank you for the links.  The top one links to see through fireplaces which is basically what we currently have.  I don’t think they are inserts so wouldn’t produce much heat.

The second link had some potential options.  One of those we had looked at but they don’t make in the US anymore and I think was too big.  I will look at the other ones. I was only aware of one see through wood stove available in the US and it was too big. Hopefully one of them will work.


The other option we are considering is buying an outdoor wood stove that we could hopefully hack into the duct work that is already in the room. Then we wouldn’t have to deal with the mess inside and could  seal off the fireplace and throw an led fire in there for ambiance. From what I’ve read, an outdoor one could potentially hear the entire house which would be nice in an emergency.

I have also seen ventless gas stoves.  Not nearly as efficient as our furnace but maybe an option since we alreadyy have a gas line to the fireplace.

Simplest solution.
Put a direct vent gas heater in that room so that it has it own gas-power heat source.

It's possible that said room takes up say 25% of the house footprint but is only getting 5% of the house central hot air, in such a situation it will never get hot. So you will have to "pipe in" a greater percentage of the central air into that room, maybe with a faster fan or with more vents. Inversely you may have to partially close all the other vents in the house.

You may have to put the thermostat control in the cool room so that the heater doesn't turn off until it is warm, but the other rooms might over heat unless you partially close the vents their thus slowing down how fast they heat up.

You could also upgrade the insulation in that rooms if the rest of the house is R-20, go ahead and increase that room to R-50.

Maybe the central air wasn't rated for the entire house and you need a bigger unit. Maybe the vents to the cold room has too many bends or the vents tubes are smaller or maybe the vent tubes have too many bends in then which effectively make it partially close. It's possible that the cold room is getting it's air sucked away and so it has to get makeup air from outside, thus making it colder than it should be.

Some ideas I have used;
- Tall ceilings can take a ceiling fan and they move hot / warm air back to the floor
- Those large windows if uncovered will be sucking heat out, pelmets on them would help if you have curtains now
- I built a similar tall ceiling house at about the same time in Australia, vaulted ceilings often had about 2 inches of insulation.
- Is the floor insulated?

I suggest you may have a draft problem if the basement door closes itself.
Maybe get a beekeepers smoker and use the smoke to detect draughts, I used cigars in the past!
I also use a laser temperature gun, they are not expensive and I check temperatures around the place.
I work in the area of efficient small homes so I am anal about finding leaks.
S Eengis idea of an additional heater may be the best if you dont want to rip all the pipes apart and start again.

BUT, could you plot all the ducts on a sheet of paper and work out what is going on?

We have a thermal camera and look forward cold spots but haven’t been able to find any apparent bad leaks-  they are definitely there, though.  Ironically, our house is much warmer when it is -20F because all the leaks aparently seal from the cold.

We have tried closing vents and nothing seems to help.  We have traced every duct to every vent.  I do think the cold air returns are a huge part of the problem. The furnace is not undersized.  If anything it is oversized.

The upstairs is a good 10 degrees colder than the downstairs.  The cold room is below freezing in the dead of winter.  It does have insulated floors.  

I’ll look  into the direct vent gas heater.  That might be the best solution.  

Thank you all for your suggestions.  Feel feel to post more if you think of anything.

Mary Osterburn wrote:

I do think the cold air returns are a huge part of the problem.

I have a friend living in a 150 yr old farm house in Nova Scotia (ie not nearly as cold as your climate, but regular snow). She was having problems with inconsistent heat distribution and her dad installed a small fan in the upper corner of the door to help push the air into it. In your case, would there be a small way to push the air that should be going through the cold air returns, out of the room into a room that returns better? In fact, now that I think of it, when we renovated our last house (that was over 20 years ago - time flies) the new location of our fridge backed onto the wall shared with the basement stairs. Hubby was concerned the fridge wouldn't get enough air flow over it's cooling coils, so we cut a hole through the drywall the size of an easy to get pair of vent covers and boxed in a simple passage and I think he added a little fan, but he may have decided once there was a foot by ~16" hole, that would be adequate to cool the fridge.

It would be really interesting if once the room has a dedicated heat source, if your issues disappear. If you decide to get the gas heater, please post the results as many people read old posts like these if they have a similar problem.