Building heat exchanger insert

[JmgAlberta]

Hello, this is my first post. Found this forum while searching around for advice on how air flows around the house and how inserts work etc.

I have two main questions at this time.

A little background.
I like to build things as that's what I do. And Inserts are crazy expensive, so I built my own heat exchanger off a few pictures I found online from a website called hasty heat. My house is in Edmonton area Canada. And is an open concept bungalow from the late 70s. Just testing the insert now, that's why it has no paint. Will probably get it ceramic coated. Basically until a few months ago when I decided to start this I had no idea even what a heat exchanger did or was. My goal is to make this thing as efficient as possible within budget. I realize what I might spend on this question will probably be the most expensive thing so far on it. I've only spent 300 or so dollars so far on materials and almost 30 hours of spare time. It heats up the area nicely. My thermometer only goes up to 50C and when I place that over the holes on the top it reaches that in seconds. The fans are from Amazon and have aluminum housings, I have gasket fabric that is good for 1000C for a barrier as well. However even without the gasket, the fans to not even get warm while running. The rectangle tube they are mounted to is 1/4" thick. And the gaurd is 1/8". The bent round tubes are 0.083 x 1" erw tube. The entire insert slides into the existing fireplace and sits there with to bolts. I am planning on making a tighter mesh as there is too much smaller coals that drop through the 1" mesh holes that the fire sits on. The insert makes the fire last much longer than it did just in the open. The door is perferrated metal screen that was easy to come by. The fire sucks air through the screen. There is an opening that hasn't been covered by a bezel yet at the bottom below the fans and ashtray. I am planning on putting the same mesh as the door is, down there.

This is my first question, would getting a piece of glass made up for the door instead of the screen cause this insert to be more efficient in getting the heat out, and making the fire last longer? If so why or why not?

Second question has to do with air pressure. The hot air coming out of the top holes can only be felt against my hand about a few feet away. Would closing them up, making them smaller, thus causing more back pressure, get the air to shoot out farther into the room?
Is this even an issue? I feel forcfully getting air farther into the room would make it hotter faster, but maybe not. That is why I'm here.

I can post more picture of the build process if you'd like and will answer questions to fill in the blanks.

Thanks,
Jake

 

[bholler]

What size and type liner is this Insert attached to

 

[JmgAlberta]

If by liner, you mean the fireplace that is in the wall of the house, I'm not sure. The both chimney sweeps I had in the house couldn't identify it. Has been there since the house was built as far as I know.

The front opening is 33" wide x 22" tall. It's tapered a bit to the back and is 18" deep. Has sheet metal side walls and firebrick at the back. I would assume the brick is just over more sheet metal. Has a brick/concrete? floor

Hope these pictures help answer your question

Thanks
Jake

 

[bholler]

If by liner, you mean the fireplace that is in the wall of the house, I'm not sure. The both chimney sweeps I had in the house couldn't identify it. Has been there since the house was built as far as I know.

The front opening is 33" wide x 22" tall. It's tapered a bit to the back and is 18" deep. Has sheet metal side walls and firebrick at the back. I would assume the brick is just over more sheet metal. Has a brick/concrete? floor

Hope these pictures help answer your question

Thanks
Jake

View attachment 319329 View attachment 319330

Ok so it's a prefab fireplace. Meant only for occasional use and with a low temp air cooled chimney. What you are doing is potentially extremely dangerous.

 

[JmgAlberta]

Can you explain why this would be dangerous? I'm gonna need more info.

The fires we've been having in here are way bigger and hotter than the ones that this new insert allows. So heat wise it's lower temp. The people before us used the fireplace all the time and we use it weekly in the winter time. This is not meant to replace the furnace in anyway. It is a supplement as the living room is on the opposite side of the house as the furnace and its sunken with large windows. Only issue the chimney sweep had was if the insert cooled the exhaust enough to cause creosote, but we burn very dried wood. And, I'll have them back next year to sweep and inspect for creosote. I'll measure the chimney diameter. I just know it's huge.

Thanks,
Jake

 

[bholler]

Can you explain why this would be dangerous? I'm gonna need more info.

The fires we've been having in here are way bigger and hotter than the ones that this new insert allows. So heat wise it's lower temp. The people before us used the fireplace all the time and we use it weekly in the winter time. This is not meant to replace the furnace in anyway. It is a supplement as the living room is on the opposite side of the house as the furnace and its sunken with large windows. Only issue the chimney sweep had was if the insert cooled the exhaust enough to cause creosote, but we burn very dried wood. And, I'll have them back next year to sweep and inspect for creosote. I'll measure the chimney diameter. I just know it's huge.

Thanks,
Jake

Because you are taking a carefully designed system that relies upon specific air flow to keep things cool. And isn't meant to be a heater. You are changing all of that

 

[JmgAlberta]

Ok, so it's the issue that's being raised is that the unit will get too hot?
I haven't covered up any of the top or bottom vents as the pics show. When the furnace place gave me an estimate when I bought the place they said their insert would sit right inside of the fireplace, just like the one I've built. Took a screenshot of the three they offered. All I see this unit is doing is taking air in on the bottom and having it heated up by the fire and blowing it out the top. The pic us off the back of it.

 

[bholler]

Ok, so it's the issue that's being raised is that the unit will get too hot?
I haven't covered up any of the top or bottom vents as the pics show. When the furnace place gave me an estimate when I bought the place they said their insert would sit right inside of the fireplace, just like the one I've built. Took a screenshot of the three they offered. All I see this unit is doing is taking air in on the bottom and having it heated up by the fire and blowing it out the top. The pic us off the back of it.

View attachment 319341 View attachment 319342

What make and model fireplace do you have?

 

[JmgAlberta]

I don't know, like I said the guys from the fireplace furnace company said it most likley was built when the house was.

The insert I've made just sits inside the fireplace like the ones I sent in the screen shot.
If it is the cooling issue. That's why Im here to get informed, to find out how and why I should or shouldn't do something. To understand why air moves in this certain application. I can't do much with information of just being told it's potentially dangerous.
If I need to modify the insert I can

Thanks
Jake

 

[bholler]

I don't know, like I said the guys from the fireplace furnace company said it most likley was built when the house was.

The insert I've made just sits inside the fireplace like the ones I sent in the screen shot.
If it is the cooling issue. That's why Im here to get informed, to find out how and why I should or shouldn't do something. To understand why air moves in this certain application. I can't do much with information of just being told it's potentially dangerous.
If I need to modify the insert I can

Thanks
Jake

Without knowing the make and model of the fireplace we can't get the manual.for that fireplace. Without that we can't give much info. Look inside the front edge for the id tag

 

[JmgAlberta]

Would you have any informative information on whether decreasing the holes would give any benefit?

Or glass vs screen?

Thanks
Jake

 

[bholler]

Would you have any informative information on whether decreasing the holes would give any benefit?

Or glass vs screen?

Thanks
Jake

Glass would help but increase the danger

 

[ABMax24]

From what I see this isn't an "insert" as such. It sits inside the stove and reclaims the heat, but the top and bottom are wide open to allow the fireplace to behave similar to it would without this.

That being said, I still wouldn't want to have a house fire caused by the fireplace and try to explain that to the insurance company.

While this unit may recover more heat from the stove, I doubt it comes anywhere close to the efficiency of an actual sealed insert with insulated liner.

 

[bholler]

From what I see this isn't an "insert" as such. It sits inside the stove and reclaims the heat, but the top and bottom are wide open to allow the fireplace to behave similar to it would without this.

That being said, I still wouldn't want to have a house fire caused by the fireplace and try to explain that to the insurance company.

While this unit may recover more heat from the stove, I doubt it comes anywhere close to the efficiency of an actual sealed insert with insulated liner.

Also if it is actually successful in extracting extra heat without any secondary combustion it will cause creosote issues

 

[JmgAlberta]

When stating 'secondary combustion' what does that mean. Is that something a normal insert does?

Besides this not being a sealed unit, doesn't it function the same as an insert?

Mind visiting the Hasty Heat website, and let me know what you think of the units they sell?

Thanks
Jake

 

[EbS-P]

I’m really impressed with the fabrication. Wish I had talent (and time) like the that.

If we had to put numbers to what you have accomplished. You probably improved the efficiency from something like negative 10% to +15% to something like 5%-25%. Current inserts are 70%-80%.

It’s polishing a turd from an efficiency point of view. Add to that safety concerns I just don’t see the benefits outweighing the risks.

With skills that you have demonstrated. Find yourself a fisher stove and install it to code and add a secondary combustion/baffle system. System efficiency would get over 65% I’d guess.

Back story of what you unknowingly waded into is that prefab fireplaces loose their UL listings if modified. Some (very very few) allowed tested inserts it be installed. The rest don’t. Any above board chimney professional will follow the units manual and not install an insert or modify (unless the manual says, for instance that a gas log set can be installed) the unit. I think your changes are significant modifications.

Now if this was installed in a code compliant masonry chimney your safety factor increases as one is not longer concerned as mischief about the venting system, but creosote is still a concern.

 

[JmgAlberta]

So with each new reply I get more lost it seems, I haven't modified anything except take out the mesh screen that was there and put this unit in.
Im confused at what the safety issue is, what is going to light on fire?
Im currently trying to google what a secondary combustion baffle is.

Thanks
Jake

 

[EbS-P]

When stating 'secondary combustion' what does that mean. Is that something a normal insert does?

Besides this not being a sealed unit, doesn't it function the same as an insert?

Mind visiting the Hasty Heat website, and let me know what you think of the units they sell?

Thanks
Jake

DGR Double Row Fireplace Grate

Upgrade your fireplace's heating efficiency with HastyHeat's DGR series grate heat exchanger. Made in the USA with fully welded steel construction, this heat exchanger features twice as many tubes as our standard GR series for an incredible amount of thermal mass, resulting in increased heat...

hastyheat.com

It’s not snake oil. It will put some more heat back into the house. But for what you spend you will never see that many $$$$s of back into the house. The devices don’t change the physics of combustion. They don’t result in increased firebox temperatures that result in cleaner combustion and higher efficiency. (One could argue that the lower the temps not increase them).

 

[EbS-P]

So with each new reply I get more lost it seems, I haven't modified anything except take out the mesh screen that was there and put this unit in.
Im confused at what the safety issue is, what is going to light on fire?
Im currently trying to google what a secondary combustion baffle is.

Thanks
Jake

Secondary combustion supplies fresh hot air to the hottest part of the firebox to reburn any smoke. The baffle traps the heat in the firebox insulating it to help achieve temperatures high enough for secondary combustion.

 

[JmgAlberta]

Am I understanding If I were to do anything but have a fire just for looks by taking my device out I'd have to get an entire new fireplace and chimney installed?

 

[bholler]

When stating 'secondary combustion' what does that mean. Is that something a normal insert does?

Besides this not being a sealed unit, doesn't it function the same as an insert?

Mind visiting the Hasty Heat website, and let me know what you think of the units they sell?

Thanks
Jake

No a normal insert is an enclosed stove that controls combustion. That increases combustion efficiency then works to extract that heat and direct it into the house. You have worked on the heat transfer but done nothing for combustion efficiency at all.

Also inserts need a properly sized liner for that stove and designed to handle the heat of a woodstove. Your chimney is only designed for the heat of a fireplace

 

[bholler]

Am I understanding If I were to do anything but have a fire just for looks by taking my device out I'd have to get an entire new fireplace and chimney installed?

That is correct for the most part. Depending upon the make and model of the fireplace an actual insert may be an option

 

[ABMax24]

Also if it is actually successful in extracting extra heat without any secondary combustion it will cause creosote issues

I guess at some point though, if there's a reduction in dilution air and an increase in heat recovered from the flue gases, the flue gas temperature will remain the same, while drawing less cold makeup air into the house and deliver additional heat to the room.

I guess I'm not totally against the concept of this, but my mind also goes to worst case "what if".

What are the rules around adding glass doors to an open fireplace? Wouldn't they increase flue temperatures due to a reduction in dilution air?

 

[JmgAlberta]

No a normal insert is an enclosed stove that controls combustion. That increases combustion efficiency then works to extract that heat and direct it into the house. You have worked on the heat transfer but done nothing for combustion efficiency at all.

Also inserts need a properly sized liner for that stove and designed to handle the heat of a woodstove. Your chimney is only designed for the heat of a fireplace

OK, I am getting it a bit now. Not going to be adding glass doors, I would assume this it's current form would be ok to still run?
Even though it's not as efficient as an insert would be.

 

[EatenByLimestone]

I think you might want to ask your insurance company on that one. If all goes to plan, they’d never know it was there. If something happens that you didn’t figure on, they could deny the claim.