Building heat exchanger insert

[SmokeNo]

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

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That's some nice metal fabbing you have there but I am concerned that, in the event of a house fire, you might (will?) have serious difficulties in collecting an insurance settlement.

 

[JmgAlberta]

Another question, what temperature does creosote form, or maybe I should ask how hot does flu gas have to be to not form it?

Even if wood is perfectly dry, would creosote still for?

 

[EatenByLimestone]

Creosote forms when water condenses on cool surfaces and then catches unburnt particles. Water is a natural product of combustion. Lowering the water quantity in the wood before you burn it just lowers the amount of water vapor going up the flue. If you can keep your flue warm, say keeping the gas 250, you can greatly reduce the amount of condensation that forms.

The other part of that is unburnt particles. Complete combustion helps keep any water that condenses on the walls of the flue from picking up material that can reignite.

 

[JmgAlberta]

What size and type liner is this Insert attached to

I haven't had a chance since getting home to inspect around the main floor fireplace but the basement fireplace I took a few pictures of. It looks very similar to the one upstairs except for the glass on it. Both have these big chimneys. And run up beside each other.

Not sure if they would be the same or not.

Is this any help?

We've never used th downstairs one as we gutted the basement from water damage.

Thanks
Jake

 

[bholler]

I haven't had a chance since getting home to inspect around the main floor fireplace but the basement fireplace I took a few pictures of. It looks very similar to the one upstairs except for the glass on it. Both have these big chimneys. And run up beside each other.

Not sure if they would be the same or not.

Is this any help?

We've never used th downstairs one as we gutted the basement from water damage.

Thanks
Jake

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Here is a screen shot of your manual. Read the warning at the beginning of it

 

[JmgAlberta]

I see in paragraph 14 that it even states do not block the air vents. Which I figured that's what they were so I did not do that in my construction.
Also I see it's insulated, which is a concern that was brought up.
Nevertheless I do plan on taking temperature readings without the heat exchanger and with the heat exchanger running to verify comparable temps. I have access in the wall construction surrounding the upstairs fireplace by a hole so I can shoot a my heat gun in there.

Thanks
Jake

 

[JmgAlberta]

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.

So I did some tests this morning with the heat exchanger still in and running on low fan speed. Just the way I would have it running under normal use, which would only be 3-4 hours at a time. I cut a hole in the drywall(pic) to take temperature readings of the side with my heat gun. I also rigged up an oven temperature gauge hanging about a foot below the top chimney vent to get flu gas temperatures.
I never meant this as a replacement for an actual insert. I just called it an insert cause I didn't know what else to call it. Bholler linked me to a manual which I ended up following in my construction by guessing the vents on the top and bottom should be open.
I had the fire burning for 3.5 hours. And checked temps every half hour.

The temperature at the top of the chimney (which is about 14' tall maybe) was a consistent 325F the entire time the fire was going. This is at the top of the chimney about a foot before it reaches open air.

The heat gun temperature reading through the drywall hole never got over 77F on the side of the fireplace box and 81F on the chimeny. (most of the time it was below that)

The temperature of the fire itself was more than 932F (my heat gun maxes out there)
The inside walls of the fireplace box was consistently around 572F.

I understand about the very rare risk of fire. This test was to see how much of a risk that is. Which to me looks very very low if any.
Let me know what you think about that please.

Thanks
Jake