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Al Burton
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# Posted: 22 Oct 2015 05:08pm
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I installed a Homcomfort DV8 direct vent propane wall heater a couple of years ago. It has been working fine but this year I decided to replace it with a larger Williams unit for those really cold days. When I uninstalled it I was shocked to find the wood in the wall was burnt black. I reviewed the installation instructions to be sure I had not done something wrong, but I had not. I thought I should post here as a warning to anyone else that might be using one of these so you can check it out and modify if required. I reinstalled this heater in another building but made some custom plates and increased the clearances considerably. I see that it appears that these may no longer be available and wonder if this is the reason.
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drb777
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# Posted: 22 Oct 2015 05:54pm
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Obviously something isn't right. Did you use specific double tube-concentric DV flue piping from the stove all the way to the end? And did you allow the recommended stand-off between the wood of the wall/ceiling and the DV piping?
From the look of the wood, you're lucky you didn't have a fire.
With my Vermont Casting DV stove, the outer wall pipe never gets hot enough to cause what you're showing. Even at that, I cut a hole allowing an additional 1" of stand-off, and then used fiberglass to fill the gap.
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drb777
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# Posted: 22 Oct 2015 06:16pm - Edited by: drb777
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From Vermont Casting Direct Vent Instructions;
Only Vermont Castings Group, DuraVent and Selkirk
Corporation venting components specifically approved and
labelled for this stove may be used.
• Minimum clearances between vent pipes and combustible
materials is one (1") inch (25 mm), except where stated
otherwise.
• Venting terminals shall not be recessed into a wall or siding.
And the minimum 1" clearance is from the outter (cool) tube, not from the inner hot, flue gas tube.
I feel sure any and all DV stoves will have similiar requirements, regardless of the brand.
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bldginsp
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# Posted: 22 Oct 2015 08:41pm
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Pretty scary. There are two things I've learned about flus that may come into play here.
-All flus continue to gradually increase in temperature if the fire is left on for a long time. Even a standard brick fireplace can eventually get hot enough to cause the wood that contacts it to burn, if you keep a big enough fire burning in it for long enough. But even gas appliances will continually heat the vent if the appliance is left on for long periods of time. I've seen numerous water heater or furnace B vent type flus that had charred the wood in the roof such as in your photos, but only when the wood was against or close to the flu.
-The space in the wall or ceiling that the flu passes through really needs to be able to vent out. In other words, the air around the flu between it and the wood needs to be able to flow out if it gets hot. What we want to do is seal everything off so air cant get in the house, water can't get in, insects etc. but the air needs to get out. Wood stove chimney flashings are designed to allow this, that is, the galvanized ones, not the rubber type.
Sounds like you had too small a heater in your cabin for the very cold days, so it was probably running continuously on a few occasions when the temp dipped down. That's probably when this happened. With a larger heater, it will run for lesser periods of time, cycling on and off to keep the cabin warm, and giving the flu enough time to cool a bit between firings.
I suggest you get a unit that is plenty large for the space you have, give as much clearance around the flu as possible, and leave a gap or some way for very hot air to get out.
From the looks of things you dodged a bullet.
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creeky
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# Posted: 22 Oct 2015 09:24pm
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wow. that's timely info Al. My homcomfort dv8 and two dv I forget (the next model up) have been on pilot for a week getting started on the cooler weather. I will be checking all three tomorrow.
thx.
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AK Seabee
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# Posted: 22 Oct 2015 10:28pm
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Scarry Al!
I have the Homcomfort DV21, 18,000 btu and so far no issues (that i know of). I have it mounted to concrete board as well as a concrete board chase through the wall. All required clearances are met.
I am heading to the cabin this weekend so will remove the metal siding and inspect the osb around the vent. I will send an update if there is an issue.
I seldom use the heater and rely mostly on the wood stove (wood is free and reliable) (propane is costly and unreliable in cold temps). To tell the truth, I was thinking about replacing it with a Toyo stove anyway.
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AK Seabee
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# Posted: 22 Oct 2015 10:30pm
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drb77, I bought my stove at least three years ago and the venting was with the stove. I honestly cant remember the maker of the venting.
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Al Burton
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# Posted: 22 Oct 2015 11:02pm
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All good info. Thanks. Here is the link to the install manual.
http://www.rural-energy.net/docs/om_homcomfort.pdf
Unless I am missing something I followed the recommendations. I did use the supplied double wall vent straight through a standard 2x4 wall. On the new install I increased the clearance around the outer pipe to 2" and put an additional metal shield in. I just thought I should bring this up as I figured if it could happen to me it could happen to someone else. Agreed it was probably too small for the application when very cold (-15f) as it would stay on almost steady without supplemental heat, which is why I was replacing it with a larger unit. There was a big difference in the clearance requirements on the new Williams unit (14k btuh). Next trip to the cabin I will take some pics of how I changed it. I think bldginsp hit the nail on the head with his recommendations. I should have put a bit more thought into it and not blindly followed the install instructions.
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bldginsp
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# Posted: 22 Oct 2015 11:19pm - Edited by: bldginsp
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I think you followed the instructions on how to instal it, but perhaps you didn't follow the instructions on how to size it. Perhaps this points to the importance of getting a unit properly sized to the space it will go into. The units all say how many square feet the unit should heat, but there is a big difference between heating an insulated 500 sq ft in Arkansas and an uninsulated 500 sq ft in Minnesota. Overtaxing any unit is asking for problems.
I'll be interested to hear if any of the other owners of similar units have had similar problems, but my gut reaction is that it's not a defective unit design, or a bad installation, but it was an inappropriate installation in terms of sizing. You said you had the unit cranking full blast for long periods- I don't know but I bet the manufacturer would say "it's not designed for that".
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Al Burton
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# Posted: 22 Oct 2015 11:36pm
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Can't argue with that I think you are dead on with your thinking there. Should certainly be used as an example of what can happen. I did heat load calculations and knew it was good for my "normal " application but when we were there for an extended period after xmas last year it was unseasonably cold so...there you go. N.W Montana if you are wondering. . As you said bullet dodged and lesson learned. Appreciate the feedback.
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FishHog
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# Posted: 23 Oct 2015 07:36am
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wow, that is interesting. I just installed a DV21 last month, only used it long enough to test. It is really a backup to wood for me, but I might have to keep an eye on this. Appreciate the warning.
Might pull my plates off and see if I can cut a bit more clearance into it, as I too just followed the installation instructions.
FishHog
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creeky
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# Posted: 23 Oct 2015 10:16am
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i just checked my dv8. It ran all last winter, the coldest winter in 44 years. 300 lbs of propane. Running all day, day after day for six months. The wall shown is closest to the heater and where the pipe should be the hottest.
Here is the picture of the outlet. As you can see it is unchanged. I will be checking my three year dv14s later in the day.
It makes me wonder, Al, did you have both the heat vent and the cool vent pipes properly attached to the unit? I know when I first put mine in I had not seated the heat vent properly and had to jiggle it in to fit.
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Al Burton
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# Posted: 23 Oct 2015 11:38am
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Creeky that is very interesting. When I removed the vent cap the center heat pipe was self supported at the other end which I would think indicated it was seated properly but obviously your unit shows no heat damage like mine. When I go back at the end of next week I will take this unit apart and really inspect closer for clues as now you really have me wondering what happened. Now it is installed in a super-insulated mechanical building that will be kept just above freezing all winter.I don't expect it to run very hard at all this year. When I was down a week ago the temps were getting just below freezing at night and the temp inside stayed about 60 with just the pilot running.
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creeky
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# Posted: 23 Oct 2015 04:02pm - Edited by: creeky
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Al I just checked my 2 two year old DV14s. Each one with about 600lbs of propane on 'em. I didn't see any sign of heat at all.
Blew some spider webs out of one of the cool air vents. Reminded myself what a pain in the behind part of one's anatomy getting that securing rod back in to the holding bolt is. That's about it.
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bldginsp
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# Posted: 23 Oct 2015 09:04pm
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Creeky- how long do your units run, on average, during a firing cycle? Do they run continuously when it is cold or are they sized large enough that they don't need to when it gets colder than usual?
Al said he had to run his almost continuously during one period of colder weather. Maybe that was just enough to char the wood.
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MtnDon
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# Posted: 23 Oct 2015 09:29pm
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Just an opinion, but unless the heater comes with a stated duty cycle like an arc welder, there should be no problem with running it 24/7.
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bldginsp
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# Posted: 24 Oct 2015 08:39am - Edited by: bldginsp
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I wonder if they test these things for that kind of use. Seems like that should be part of the testing for listing, but 'should' is one thing, and what actually happens can be another.
I looked over the manual and manufacturer's website, there is no info about sizing and no words of caution about the potential of undersizing, other than that if the room isn't being heated adequately the unit is too small.
Northern Tool advertises the DV8 as adequate for up to 300 sq ft, but the manufacturer says 200 sq ft.
http://www.usstove.com/index.php?route=product/product&path=124&product_id=983
http://answers.northerntool.com/answers/0394/product/175091/homcomfort-small-heater-7 500-btu-300-sq-ft-heating-capacity-model-dv8n-questions-answers/questions.htm
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creeky
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# Posted: 24 Oct 2015 11:20am
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Quoting: creeky my dv8. It ran all last winter, the coldest winter in 44 years. 300 lbs of propane. Running all day, day after day for six months
and no problem. Al has an install mystery.
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bldginsp
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# Posted: 25 Oct 2015 06:06pm
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But creeky I bet your units were cycling on and off during those cold months. They'd burn for a half hour at a time then cycle off, then on again. Between each cycle the flu can cool. But if the unit is undersized the burn never cycles off when it's at 15 below. The burn runs continuously for hours, gradually heating the flu and wall cavity more and more til it chars.
It's a bit counter intuitive and ironic that a smaller unit at less BTUs would make more heat in the wall cavity than a larger unit with twice the BTUs. But the larger unit would heat the room faster and cycle off with the thermostat, letting the flu and wall cavity cool. The small unit just keeps burning cause it never catches up to the thermostat, gradually heating up the wall cavity more and more til it chars.
At least that's my theory. But as a friend used to say,"Theories are leery". I think he meant that he was leery of my theory, but that's how he put it.
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KinAlberta
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# Posted: 25 Oct 2015 09:33pm - Edited by: KinAlberta
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Was the pipe wrapped with insulation at the point it touched the wood? If the insulation allowed heat to build up maybe it got very hot near the wood. You need the airspace (convection space) to circulate air and carry the heat away.
By analogy, with continuous heat being generated I wonder if this is somewhat the reverse situation to my rim joist foaming around my exterior freeze-proof water taps which are exposed to continuos cold penetration in the winter. During the bsmt reno of my house the electrician noticed that the pipe had been foamed in and said that the foam would allow the cold to reach further into the house and reach the tap's deep set valve. So I cut out some foam from around the valve stem so interior air could keep the pipe warmer as it reached the exit point in the exterior wall.
I felt stupid for not realizing this. Adding insulation keeps more heat in the house but it also shifts the freezing point deeper into the wall since less heat is escaping. (Insulating around a pipe means the insulation should transmit more heat or cold further from, or along, a pipe.)
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bldginsp
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# Posted: 26 Oct 2015 08:12am
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KinAlberta- yes it seems roughly analogous. The point is you have to think about what you are doing wherever you do it. That sounds obvious, but how many times have I done something with X intentions in mind, only to find out later that it had unintended consequences. Physics happens, regardless of the best laid plans of mice and men.
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creeky
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# Posted: 26 Oct 2015 08:30am
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Quoting: bldginsp he was leery of my theory
I'd stick with that.
This is an interesting post in that we have an anomalous result from a real installation. I look forward to more real data from Al.
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Al Burton
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# Posted: 26 Oct 2015 01:13pm
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There was not any insulation between the out fresh air pipe and the wood. There was however around the outer pipe inside the wall cavity. I am hoping to get there later this week but not sure yet if that will happen. When I do get there I will examine everything closely and let everyone know what I find.
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bldginsp
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# Posted: 26 Oct 2015 09:00pm - Edited by: bldginsp
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Al- I tried contacting the manufacturer with this question, but I'll be surprised if I get an informative response. The legal issues are probably such that all they can say is "follow the instructions". I'll post it if I get a response.
Creeky- you still haven't told us if your units were cycling on and off for the period of months you had them in operation. If they were not, and burned continuously overnight, that would disprove my theory, of which you are so leery.
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creeky
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# Posted: 27 Oct 2015 09:24am
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I figured that someone familiar with a dv propane heater would go 300 lbs!!! and realize that the heater got a heck of a work out. and that is indeed the fact. the coldest winter in 44 years meant weeks of -30 weather. At -35C and windy my heater goes on and stays on.I liked it. No clanging start ups and cool downs at night.
Asking questions (aka gathering data) is usually better than idle speculation when solving problems. And Al's problem is pretty serious I think you would agree. And is of real concern to us as what's got these heaters.
Who did you contact? US Stoves? The mfct? What's their name again? Specifics are important.
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bldginsp
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# Posted: 27 Oct 2015 12:44pm
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I went to the US Stove website and used their standard contact info. Again I doubt we will get a substantial answer from them because they don't want to open themselves to liability issues, but maybe.
And what I said, or theorized, is not entirely speculation. I have seen many situations with charred wood around standard flus and asked the question before- why do some char and others not. But I have not seen it with direct vent wall flus specifically.
The main issues are always burn time and ability to dissipate heat. An in-wall flu is the worst case scenario for heat dissipation. Flus through roofs usually have a means for hot air to escape. But if it can't, and the burn doesn't stop, heat must gradually build if it can't dissipate through the surrounding materials.
An analogous situation is a wall heater, the type with an oval flu that goes up in a stud bay to the roof. Not much room in that stud bay for surrounding air but if installed correctly it will vent. I once saw one that had wood paneling installed on one side of it. When they demo'd it the paneling was charred. The owner said,"We never used the heater cause when we did it smelled smokey".
A lot of posters on this site, including myself, suggest to our inquiring newcomers that they instal direct vent wall heaters. I want to feel confident that we give them the best info we can, based on the broadest of experience, not just a few examples or just theories. I hope the manufacturer responds- they are the ones who hear about the realities of these things, but they are also the party least likely to share that info if they percieve that doing so could open them to liability issues. Their best position is to tell people to instal according to the listed instructions, and leave it at that. Can't go wrong with that. But then we don't get the benefit of their broader experience.
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NorthRick
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# Posted: 27 Oct 2015 12:53pm
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Not sure what went on with Al's setup, but on mine (Orbis brand) the intake pipe surrounds the exhaust pipe. So cold outside air is constantly drawing past the walls of the hot exhaust pipe. The heater runs more when it is colder and, therefore, the more it runs the colder the air that is cooling the exhaust.
I haven't taken mine apart to look at it, but I've never smelled hot or charred wood from either side of the wall where the heater is mounted.
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bldginsp
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# Posted: 27 Oct 2015 02:12pm - Edited by: bldginsp
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NorthRick- that is an excellent description of how all direct vent flus are supposed to operate, at least in theory. But as my friend used to say, 'theories are leery'. If the burn continues for hours the flu should stay cool. However, practical experience shows that in some cases a flu with a non-stop burn will very gradually heat up over time. The exterior intake pipe must be mechanically connected to the metal housing of the furnace, and so conducts its heat. Is the cooling effect of the intake air enough to prevent gradual heat increase in the intake pipe? It should be- in theory.
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creeky
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# Posted: 29 Oct 2015 11:44am - Edited by: creeky
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Well. This is interesting. I found the new installation manual for the Eskabe (the Mfct of "homcomfort") direct vent heaters.
If you compare pages 8-9 on the previous model and the current model you will see they have added a "standoff" on the exterior of the building. The internal cutout appears similar to the previous installation guidelines.
Current model installation manual
They have also added this line:
Minimum clearance between pipes and combustible materials is one (1) inch (25.4 mm).
For those of you with direct vent heaters, you may wish to have a look/modify your installation.
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