Can't Keep Heco 520 Cool

[Isaac Carlson]

I have never closed a pipe damper more than about half way. Sounds like you are on track. The secondaries are probably pushing a bit of heat around the end of the baffle, as you have said. Do you have a way to extend the baffle out another couple inches past the tube? I would try that to reduce the stovetop temps just a bit. It might take it down 50+*.

 

[bholler]

I have never closed a pipe damper more than about half way. Sounds like you are on track. The secondaries are probably pushing a bit of heat around the end of the baffle, as you have said. Do you have a way to extend the baffle out another couple inches past the tube? I would try that to reduce the stovetop temps just a bit. It might take it down 50+*.

I used to run 2 in a row and when in the teens outside both would be closed.

 

[mattie5960]

I used to run 2 in a row and when in the teens outside both would be closed.

Funny you say this. I was wondering if I might want two of them to slow it all down even more. My house sits almost at the top of a hill, with a large pond/ small lake in the valley a few hundred yards away. There is always, always, always a breeze here. Last night was uncommonly calm. And again, it was also 40 degrees outside.

I have never closed a pipe damper more than about half way. Sounds like you are on track. The secondaries are probably pushing a bit of heat around the end of the baffle, as you have said. Do you have a way to extend the baffle out another couple inches past the tube? I would try that to reduce the stovetop temps just a bit. It might take it down 50+*.

I'm not sure how I could do that without buying a larger baffle. Do they sell large baffle squares that you cut to size yourself?

Regardless, when the first fire burned down I put four medium- large splits in and was able to keep it under 800 the whole time. Within half an hour the stove top temps were dropping to under 700 with a flame still on the log. I was able to choke the secondary to only 10% or 20% this time. Only needed to open it to 3/4 to get the fresh splits burning to begin with!

I just happened to wake up about 6 hours after starting the second fire, so I checked on it then and it had burned down. Stove top temp at 300 on the nose. The firebox wasn't even half full at the start, so that's not a bad burn!

 

[bholler]

Funny you say this. I was wondering if I might want two of them to slow it all down even more. My house sits almost at the top of a hill, with a large pond/ small lake in the valley a few hundred yards away. There is always, always, always a breeze here. Last night was uncommonly calm. And again, it was also 40 degrees outside.

I'm not sure how I could do that without buying a larger baffle. Do they sell large baffle squares that you cut to size yourself?

Regardless, when the first fire burned down I put four medium- large splits in and was able to keep it under 800 the whole time. Within half an hour the stove top temps were dropping to under 700 with a flame still on the log. I was able to choke the secondary to only 10% or 20% this time. Only needed to open it to 3/4 to get the fresh splits burning to begin with!

I just happened to wake up about 6 hours after starting the second fire, so I checked on it then and it had burned down. Stove top temp at 300 on the nose. The firebox wasn't even half full at the start, so that's not a bad burn!

At this point I wouldn't change anything else about the setup unless you get a meter to measure draft. Just learn the stove and what timing works etc. You may end up with a second damper next year when temps drop but you have come a long way

 

[SpaceBus]

At this point I wouldn't change anything else about the setup unless you get a meter to measure draft. Just learn the stove and what timing works etc. You may end up with a second damper next year when temps drop but you have come a long way

I would also start trying to circulate air around the oven to control the burn. I've never seen a cookstove manual that says not to use the oven when pushing the stove for max heat output, and I read at least eight or more when I was shopping for cookstoves a few years ago.

 

[Ashful]

I used to run 2 in a row and when in the teens outside both would be closed.

Tell me if I'm wrong, but I'd expect you reach a point of diminishing returns. First damper makes a huge (eg. 3x - 4x) difference in draft. Then second has a much smaller effect, such as 3x-4x on the already-reduced amount, and so on. Correct?

Using my own chimney numbers, my single damper gets me from 0.21 to 0.05"WC, let's call it 4x reduction, or a 0.16" difference. I'd expect a second one to give me another 4x reduction, but on the already reduced 0.05"WC, that's only a small 0.01" difference.

 

[mattie5960]

Tell me if I'm wrong, but I'd expect you reach a point of diminishing returns. First damper makes a huge (eg. 3x - 4x) difference in draft. Then second has a much smaller effect, such as 3x-4x on the already-reduced amount, and so on. Correct?

Using my own chimney numbers, my single damper gets me from 0.21 to 0.05"WC, let's call it 4x reduction, or a 0.16" difference. I'd expect a second one to give me another 4x reduction, but on the already reduced 0.05"WC, that's only a small 0.01" difference.

Your logic makes sense (point of diminishing returns), but you did your math wrong.

.20 x .25 = .05
.05 x .25 = .0125

So the first one, a 75% reduction was a .15 difference in draft. The second one also produced a 75% reduction, but for only a .0375 difference in draft.

If the initial draft was more like .4 than .2, two dampers might work out (or if initial draft was lower, you might not have them both completely shut). But I don't actually know what mine is.

 

[mattie5960]

Here's a picture of what I mean by the secondary burn constantly lapping around the left of the baffle against the bottom of the stove top. This one was taken last night, but its doing it now with a smaller secondary burn, too. It's even worse if there's a flame directly beneath the left side of the firebox, because there's nothing keeping the flame from getting above the baffle.

Is the idea that pretty much all the flame should be beneath the secondary air holes, with none traveling past the baffle like this?

 

[Ashful]

Your logic makes sense (point of diminishing returns), but you did your math wrong.

Not at all. I was just rounding. I'm an Engineer, not a Scientist.

If we're splitting hairs, we're not counting the restriction of the stove itself, in that math. Since I don't know the number for that (three unknowns, but only two equations), I'm assuming it's contribution is small enough compared to the dampers, that it can be negated.

 

[bholler]

Every chimney and stove will react differently to the restriction of a damper. And the resistance in the stove is a big factor as well.

 

[begreen]

 

[Ashful]

View attachment 294317

Damnit, begreen… you could have at least given me a few more posts to have fun with these guys, before dropping that.

 

[Isaac Carlson]

Is the idea that pretty much all the flame should be beneath the secondary air holes, with none traveling past the baffle like this?

Yeah. Pretty much. The idea with secondary burn is to keep the firebox really hot and supply pre-heated oxygen (800+F) to burn the smoke/gasses while the flames in the firebox and only letting completely burned exhaust out the flue. If the flames are lapping too far past the last burn tube, that means there is too much burnable gas for the air being provided. Turning down the primary air can help, but the temperature of the firebox is what drives the off-gassing of the wood, so a hotter firebox will make more gas which needs more air....it is a self feeding cycle, but we need to regulate it so we don't melt our stoves. Finding the balance can be difficult because wood load, air supply, firebox size/shape, draft, air temperature, stove insulation, burn tube design, baffle material, etc...all change how a stove burns. You almost need an engineer on site to taylor the stove to the install, because they are made to fit a variety of conditions.

 

[bholler]

Yeah. Pretty much. The idea with secondary burn is to keep the firebox really hot and supply pre-heated oxygen (800+F) to burn the smoke/gasses while the flames in the firebox and only letting completely burned exhaust out the flue. If the flames are lapping too far past the last burn tube, that means there is too much burnable gas for the air being provided. Turning down the primary air can help, but the temperature of the firebox is what drives the off-gassing of the wood, so a hotter firebox will make more gas which needs more air....it is a self feeding cycle, but we need to regulate it so we don't melt our stoves. Finding the balance can be difficult because wood load, air supply, firebox size/shape, draft, air temperature, stove insulation, burn tube design, baffle material, etc...all change how a stove burns. You almost need an engineer on site to taylor the stove to the install, because they are made to fit a variety of conditions.

Not an engineer just someone with equipment to measure draft. Or some patience to figure out what works with your particular setup. In my experience most of the time I see lots of flames wrapping around the baffle it is due to excessive draft.

 

[Isaac Carlson]

Just sharing for the heck of it.

We have a fire going in the cookstove to take the chill off tonight. Not a big fire. Here are the current temps on our cookstove. The handheld thermometer maxes out at 750 and anything higher just reads as hi. Actual stovetop temp is ~800. This is a perfectly normal burn and temp for our stove.

 

[begreen]

What does it read on the body of the stove top, not on a cook plate over the flames?

 

[Isaac Carlson]

Anywhere from 550 to 750

 

[Ashful]

Anywhere from 550 to 750

That sounds like pretty typical stove-top temperatures, for any of our normal (heating) woodstoves.

 

[mattie5960]

Alright, I'm back after a few days of experimentation with some info I'd like to share, both to update the crew here, but also in hopes to level the learning curve a bit for anybody else who decides to buy this stove, especially if they've never owned anything like this before.

I called DS Stoves (Heco) mid-last week to talk about the difficulty I was having keeping the stove cool. The gentleman I talked to was clearly speaking as candidly as he could without opening himself or the company up to any kind of liability, and he was cautious not to go against anything the manual said. He did say some things that were reassuring, though, and insightful to how the manual was written. First, he confirmed that the stovetop temp should be measured over the left cookplate, which is directly above the firebox, and is also directly exposed to secondary flame a lot of the time. The reason for this he said was simply because prolonged exposures to temperatures over 800 are going to run the risk of warping. He mentioned that Heco actually stocks extra left cook top panels for cases where customers accidentally warp them from over heating. Reassuringly, he did say that approaching and even exceeding this temperature for brief durations should be expected when using wood, since wood puts off a lot of heat when it's gassing. He said you just don't want it over 800 consistently, for "hours on end".

Next, I asked him about engaging the oven side of the stove to keep the stove top temp down and more evenly distribute the heat within the entire stove. Here, again, he sided with the manual's recommendation to keep the oven off when you're only using the stove to heat. In support of this stance he said two things specifically, "The oven isn't built to the same spec as the firebox", and "When you engage the oven, you have to worry about fly ash getting to that side of the stove".

So, after the conversation, I got thinking about what he means when he says the oven side of the stove isn't built to the same spec as the firebox side. Taking the cook plates off the stove, it's pretty clear what he means. Obviously the firebox is lined completely with firebrick. The oven side is by-majority exposed metal. Here's where his comment about fly ash is especially important -- fly ash comes from coal (not wood), and it quickly causes rust if it's not cleaned out. My suspicion is that DS Stoves holds a blanket recommendation to run these stoves with the oven side off in case the user is burning coal, because it's unlikely that the user going to clean out the space around the oven often enough to prevent a premature rust issue if they're burning coal.

Another point of support for opening the oven side of the stove when burning wood is that the entire left side of the oven is protected by the same baffle material that the top side of the firebox is. The entire air channel all the way down the left side of the oven is protected from exposure to direct flame (unlike the underside of the left cook top).

Probably the biggest point of support for opening the oven side when burning wood is that the whole dang thing just works right when you're circulating the air around the oven. A 650-degree stove top with the oven engaged puts off much more heat than a 650-degree stove top when the oven is not engaged. Go figure.

I did install a second stove pipe damper over the weekend, and even with both dampers completely shut down, I was unable to keep the secondary flames from lapping right up against the bottom of the left cook plate when the oven was not engaged, sending it over 800 degrees. This might not be so bad with small loads of wood, frequently reloaded, but who wants to have to reload their stove every 90 minutes or so?

I have since been running the stove almost entirely with the oven engaged. The only exceptions to this are when I'm getting a new fire started, and when I'm getting new logs burning after a reload. The reason for this is that I have found that engaging the oven is about equivalent in draft reduction to shutting down a pipe damper when the oven is not engaged. When running the stove with the oven engaged, I've been able to load up the firebox on a hot bed of coals, and keep the stove top temps under 800 for the entire duration of burn. There's usually a spike in temps early on as I'm getting the new logs going, but once I engage the oven side of the stove, stove top temps tend to stay between 550 and 700, depending on how much fresh wood I've loaded in.

The stove burns very cleanly. I've had overnight burns of 6-8 hours, and I've yet to truly fill the firebox. I've probably maxed at 70% full, or so, so far. I've experimented with the bi-metal regulator, but I haven't been using it for regular burning when I'm around the house. I've found that if I try to use it to get fresh logs started that it doesn't respond quickly enough to the rate at which the logs (and stove) get hot. Consequently, the fire is allowed to "run away" until finally, the bi-metal regulator shuts down the primary air. At this point, the fire smolders down until the bi-metal regulator finally opens up again. I've seen the stove "cough" a few times in my experimentation, once the primary air finally opens up again and all the smoke in the stove tries to ignite at once.

I think the best use of the bi metal regulator might be for situations where you've got new logs on the fire, and the stove is calming down, but you're not sure the secondary air on its own will keep the logs going. If you don't want to sit and babysit the stove, you can wind the bi-metal regulator temp to whatever temperature the stove is currently burning at, and if it starts to go out, the primary will open up to keep it from smoldering while you're gone.

I keep the secondary air wide open all of the time. The only exception is if I'm going to bed and the logs are basically burned off, I might back the secondary off to 50% or so to avoid burning the embers out too quickly.

I'll also say that the stove is very, very easy to clean. You pop the 3-piece top off, and you can remove the firebox baffles, and clean the top and sides of the oven air circulation passages. There's a hatch beneath the oven to open to let you clean the air passage underneath. There's also a hatch at the exhaust to clean that chamber, as well. If creosote builds up in the stove, the design of the stove will not make clearing it any more difficult than it has to be.

So, there it is. Those of you that recommended running the oven side of the stove with wood fuel were correct in my evaluation.

Thank you, all! I hope this thread is helpful to future cook stove buyers.

 

[begreen]

The "secondary" air is actually primary air for the airwash in this stove when burning wood. The thermostatic "primary" air is under the fire air for coal burning. Leave that off for wood burning, except maybe for the initial start.
I agree that running with the oven engaged is the normal mode of operation. It distributes then heat across the stovetop, providing that nice hot to simmer range of temps for cooking as well as heating up a lot more mass. That is the way I always ran our cookstove once the fire was burning well. However, I would turn down the airwash air ("secondary") as much as necessary without squelching the fire to smoldering. Leaving this wide open may be why a second damper was thought to be necessary. This is controlling the stove by the exhaust instead of by the intake air.

 

[SpaceBus]

I'm glad you used the oven damper! Your assumption about not using the oven during coal use sounds solid and I would agree. I clean out the inside cavity of my cookstove twice a season with an ash vac. Whenever it gets sluggish to start I know it's time to clean, but I also lift up the cooktop sometimes to check and see what's going on.

 

[Hoytman]

Coal burning:

Zero cause for concern on any part of that stove with fly ash. If their was, no reason to advertise it as duel fuel, no reason to build the stove to handle both. They built it to handle it, which is why there's so much stainless steel in that stove. It is built for it.

The issue is moisture infiltration mixing with the fly-ash when the stove isn't being used. That is when the corrosion takes place...and it can be rapid.

Keep it clean. Keep it dry...either by disconnecting from the chimney, or simply by using a couple incandescent light bulbs inside the stove (oven controls open as in baking) to keep things dry (a better way...recommended by at least one Amish stove manufacturer).

Or...simply burn wood.

Would love to see a cooking video of your stove in action.

 

[bholler]

Coal burning:

Zero cause for concern on any part of that stove with fly ash. If their was, no reason to advertise it as duel fuel, no reason to build the stove to handle both. They built it to handle it, which is why there's so much stainless steel in that stove. It is built for it.

The issue is moisture infiltration mixing with the fly-ash when the stove isn't being used. That is when the corrosion takes place...and it can be rapid.

Keep it clean. Keep it dry...either by disconnecting from the chimney, or simply by using a couple incandescent light bulbs inside the stove (oven controls open as in baking) to keep things dry (a better way...recommended by at least one Amish stove manufacturer).

Or...simply burn wood.

Would love to see a cooking video of your stove in action.

Good advice we also spray coal stoves down with wd40 at the end of the heating season as well to keep moisture away from the residual ash on the metal. The same for pipe and stainless chimneys or liners.