Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: halfpress on December 10, 2010, 08:11:43 AM
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We've been going through a major ordeal with the installation of our new Heatmor 200CSS for the last month. The bulk of the ordeal was hiring some guys to do the install that seemed fine at first (one even owns a Heatmor), but who clearly didn't know what they were doing. It's a long and sordid story that I won't recount here since it's, for the most part, irrelevant now. I hired someone else to undo what they screwed up and we've got heat now. We're not bug-free yet, though, and I was hoping for some insight from the group here in addition to the research my dealer is currently doing.
In a nutshell, our system is a 200CSS on a concrete pad about 65 ft from the house and only slightly downhill. The top of the furnace is probably roughly at the level of the pipes inside the basement under the floor (single story with unheated attic). Our house is close to 100 years old and we have cast iron radiators (about 18 of them, I think). The system was formerly steam with a propane boiler that was costing us a fortune, hence the switch to a wood furnace this fall. This also meant moving the radiators from steam to water which they are capable of since they are the two-pipe design (feed on the top of one end, return on the bottom and parallel paths across through the columns).
First off, we knew we needed to add bleeder valves to the radiators and we fought through that hell. They had screws painted and sealed into the hole where the bleeders would go and it took a LOT of work (heating with a torch, etc) to get those out. Ultimately, they all came out fine with the threads intact and we put little key-turn (with a slotted screw head) bleeders in each one. They seem to work fine since we can bleed off air when the pumps are running and, after some bit of air (if any), water comes out in a steady stream or jet. We also opened the little contraption on the return end near the floor on each radiator and removed the old steam-related condensation trap mechanisms.
The feed into our house is a bit large. When the HVAC guys first looked at our old system, they saw that the head pipe from the old furnace was 2.5" in diameter. It T'ed toward the front and back of the house where the pipes step down fairly quickly to 1" and/or 3/4" pipes that go up into the radiators and out from the radiator returns. They felt they needed to meet that with 2.5" of water volume (this is an issue in serious contention now since in a closed, zero pressure system, I didn't think we had such issues once the system is full and the circulators are running). Whatever the case, the 200CSS has a pair of pumps mounted on its supply that connect to two 1.25" PEX feeds into the basement (that stuff alone was a huge holdup in our install since nobody has fittings, tools, etc., without special order). I thought they were going to combine those 1.25" into one 2.5" source of water right into the main 2.5" cast iron pipe from the radiator system. Instead, they ultimately took the T'ed segment of that 2.5" pipe out making it what would seem to be two separate radiator circuits in our house. They feed each of the two 1.25" PEX lines right into separate 2.5" lines which go on to step down and feed the radiators. There are, of course, two 1.25" PEX returns to the furnace to match these feeds. The cast iron original feed lines in the house run a loop and the radiators come off of them in separate feed and return lines, so valving off and one or more radiators in the house doesn't stop the flow downstream to others.
So, long and short of it, is that we'd appear to have two 1.25" PEX feeds going into what would seem to be two separate loops in the house radiator-wise, each with their own 1.25" PEX return to the furnace. I'm quite certain now that these two separate loops do cross over somewhere in the plumbing under the house since it is possible to push water into one feed at the furnace (using a garden hose) and, ultimately, get water out of both return line boiler drains. Whether this potential crossover inside is a problem or not, I don't know.
ANYWAY... for over a week now we've been running it and it is heating the house pretty well. No real complaints there. Here is our problem:
We keep losing water. I've had someone go through all of the crawl spaces under the house and they found absolutely NO leaks in the radiator plumbing. No damp spots. No water. No weeping. Just old, heavy, solid pipes with fittings you'd probably never get apart. This part of the system seems to be intact.
We had some leaks in the feed valves of the old radiators at first (they were ancient), but all of the leakers have since been replaced with new brass radiator valves and they seem fine. The old ones that didn't leak seem to still be intact. We've seen NO signs of water in the house on any part of a radiator after those replacements went in. Not on the floors, at the connections, etc. They, too, seem intact.
But the Heatmor bladder keeps going flat a day or so after topping it off and I can begin to hear gurgles in the radiators when the pumps stop or start. When the system is first topped off and the bladder is at a proper volume, anytime the pumps stop (thermostat satisfied or switched off manually) water comes out the pipe on the roof of the furnace. This will happen repeatedly as the pumps stop throughout the next 12 or more hours until, I suppose, enough water has come out that this doesn't happen anymore. By this point, though, the bladder stays flat all the time and I'm quite sure we've got less than proper water leading to possible boil-offs, overtemps, etc.
If the pumps are running, I can bleed all the radiators and, after a top-off of the Heatmor, get very little air out and almost immediate water from the bleeder valves. I discovered the other night that if I open those bleeders with the pumps off, the hissing I am hearing (which will go a LONG time) appears to be water being sucked into the radiator rather than bled out. So, obviously, I've stopped doing that. I now only bleed them (mostly to test the system) when the pumps are running at the furnace.
We had one radiator whose valve hadn't been replaced at first and it hissed all the time. In retrospect the other day, I realized it might have been sucking air in as much as anything. It has since been replaced and is now quiet. That radiator, too, has no bleeder on it due to a cramped space (no room for the valve). Even now with a new feed valve on it, I can hear it making trickling/tinkling noises inside faintly. I suspect it has a great deal of air - even though it heats up pretty well - that has never been bled off. I am tempted to shut that radiator off entirely or even remove it and cap off the feed and return pipes (as we've done with one other in the house).
So, in summary, no matter what I do, we seem to keep losing water and I suspect it's all coming out the top of the Heatmor rather than from a leak somewhere. The suggestion from the dealer right now is that we have an air leak somewhere (?) that is allowing pressure to keep building and blowing the water out of the furnace. If we do, I've not found it. I also have a hard time imaging we have an air leak if water wouldn't come out in a visible way when the pumps are on or even off. Thus far, we've found NO leaks of water... so how would we get leaks of air? Maybe a leaky bleeder valve that isn't losing water? If so, would I not hear that air sucking in with close inspection?
This is getting pretty frustrating, so I'm hoping someone with a wood furnace and old cast iron radiators might share their experience and point out something we might be doing wrong. If anyone else has ideas on how to test our system or changes we can make (hopefully minimal) to get this thing running right, we'd be forever grateful.
Sorry for the overly long post, but there is a lot to the story. I can answer any questions anyone might have, too, if I've overlooked a detail here that is useful.
Thanks!
- Aaron
Sweet Briar, Va
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Do you have any check valves installed? Can you shut off everything and watch top of furnace to see water coming out?
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Thanks for the reply.
Here's the easiest way to describe it:
1 - I top-off the furnace, which I will do with the pumps running to be sure I'm filling all volume of the house and furnace itself. I continue this until several gallons run out of the top of the furnace indicating it's full and all air is purged.
2 - As soon as the pumps are stopped, some number of gallons instantly blow out the top of the furnace at the ball-covered blow-off tube.
3 - Start the pumps again... everything runs fine.
4 - Turn off the pumps again - more water comes out the top.
I'm pretty sure this process repeats itself every time the thermostat cycles off until such time that what is blowing out the top is too low to do it any longer. At this point, the bladder is also flat and I think I'm heading toward the water possibly being too low for the furnace overall. Eventually I get over-temperature shut-offs of the blower a lot... possibly the aquastats not getting a good measurement any longer.
I am also not aware of any check valves anywhere in the system. How might those come into play in this design?
Any help is much appreciated!
- Aaron
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I would guess that the problem is the water in the radiators is heating and cooling causing the water to expand and contract. I would think the only way to solve your problem is to pressurize your radiator system and use a heat exchanger between it and the furnace. I know of a guy near me that had the very same problem with a Heatmor and that was the way he solved the problem.
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you said your furnace was below the level of your house? it sounds like when you turn your pumps off the water is flowing downhill and overflowing your furnace. if so, a check valve on both supply lines would stop them from flowing back down, but I'm not sure how to stop the returns from flowing back down as well.
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Yeah, I'm really hoping to avoid the heat exchanger approach... cost, complexity and reduction in efficiency that goes with that whole package. :(
Does anyone know if electronic zone valves can help? I picture them on the return lines tied to the circuit with the pumps (and the pumps having check valves to prevent backflow). The pumps stop, the zone valves close off the radiator side from the furnace side and remain that way until such time that the pumps are fired up again.
This stems from some thinking that WillieG spurred in his reply to me earlier concerning gravity, use of some three-way valves, etc.
Thanks!
- Aaron
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the plate heat exchanger would work that yonder spoke of (i don't see any loss of efficency?)
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The gravity suggestion has come up a couple of times. I just happened to be talking to my dealer, too, and he somewhat agrees... but he's suggesting that we should have enough of a vacuum in this system to prevent that. He's basing that, too, on a vacuum holding water up to some 30-odd feet and the difference between the furnace top and the radiators is nowhere near that. It could be several feet... I doubt even ten feet, but I've certainly not got a precise number.
The gravity scenario really seems to fit, in my mind... but he's disputing it and leaving me a bit confused on the matter. He still leans toward an air leak in my radiator system creating pressure that causes the blow-offs...
One of his techs, too, is suggesting that since our system started as steam and is now water, that there is a loop somewhere in the radiator feed/return plumbing common to steam that's causing trouble. I've seen some evidence there might be a loop since what are supposedly two separate radiator "circuits" in our house (each with its own supply, pump and return line to and from the furnace) appear to cross somewhere. I say this because we opened both return drains on the furnace one night, attached a hose to ONE of the supply drains and ultimately got water out both return drains. I'm going to repeat that test this weekend.
I also wonder if, with said possible loop, the two pumps at the furnace could be working at cross purposes somehow and creating pressure or other issues. I plan to try running the whole system off just one of the two pumps this weekend (they are Grundfos XL's - have low/med/high settings) and seeing if we get blow-offs AND whether it, in fact, can heat all the radiators.
So, gravity, pressure, loops, air leaks... you can see why I'm going nuts. It's heating our house and I'm getting a handle on the burn cycle, wood load, etc... I just need the freakin' thing to stop losing water so I can go on with my life this winter. :)
Thanks!
- Aaron
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how about check valve on feed line so no water can go back
add a zone valve in the return line at the house
the zone valve would shut off and on with your pump the pump kicks on and the zone valve opens, pump pushes water through the check valve and through your system then through the open zone valve and back to the furnace. room reaches set poing and pump shuts off, also zone vavle on return line closes. now water can pass through teh zone vavle back to teh stove and no water can back up through the check valve on the feed line, so no siphoning of the rads due to the OWB being lower than the rads
I think that would work if you do not want to isolate your OWB from your house system
I post th is here in case there are faults and someone can pick up on them
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Willie:
You describe precisely the scenario that has been coming together in my head tonight - and it's thanks to all of your responses collectively getting the wheels turning. Let me say again that I really appreciate you all slogging through my description and sticking with this topic. :)
So I can totally see this scenario working. I had described the idea an hour or so ago to my dealer and he looked up prices. We confirmed my pumps don't have built-in check valves, so we'd need those for about $17 a piece. The zone valves at 1.25" (to fit our PEX lines) were like $135 each or so. In the grand scheme of this headache, these are worth every penny.
But before we proceed on it, I agree with Willie and I would like to know if anyone sees flaws in the concept. The first thing that springs to my mind is timing: how quickly do those zone valves shut? When the pump stops, will they close so fast that no water can escape? I need to do a rough timing test and see how quickly after my pumps stop that the water comes out of the furnace, too.
Any thoughts?
- Aaron
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Zone valves take about a minute to close. I agree that zone valves on the return lines and check valves on the supply lines would be a great solution. Though your system should technically have enough vacuum to hold the water up, any little air leak kills the vacuum. You've said you have multiple air leaks you think you've fixed, but you might have more you can't hear. Also, the little rubber ball on top of the 200CSS doesn't exactly make an airtight seal.
Probably a more permanent solution for just a little more money would be to take your 1.5" PEX loops and circulators and make a closed loop out of them right at the Heatmor. Run them through one or two heat exchangers and put a small circulator (Taco 003 or 007 would do it) to circulate the Heatmor water through the other side of the heat exchanger. That would completely eliminate water loss from your loop and then the only way to lose water from the Heatmor would be to have a boil over.
Two of these shell and tube exchangers would give you 170k BTU's and do the trick
http://www.outdoorfurnacesupply.com/series-85000-pool-heat-exchanger-p-183.html (http://www.outdoorfurnacesupply.com/series-85000-pool-heat-exchanger-p-183.html)
Check valves and zone valves would be an immediate solution, but you may consider the heat exchanger idea in the future. It would separate the house from the Heatmor and separate an old questionable system from your $7000 OWB. It would also allow you to introduce no oxygen into your radiator system and keep them from rusting out longer without using rust inhibitors.
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So if you would go with check valves and zone valves and on a warm day the pumps don't run for a few hours. The water temps in the rads drop to room temps, wouldn't that cause a vacuum on the system? I don't know how much water is in your 18 rads but with heating and cooling that water has to have some expanding and contracting. If you put in zone valves I would recommend a pressure tank somewhere on the system. I installed a furnace to a home three years ago where the existing boiler had developed a leak. I eliminated the boiler and put in a new 40 gal. hot water expansion tank and a 1" 30 plate heat exchanger. The furnace pump ran 24/7 and the existing pump on the boiler system pulled the water through the flat plate when the thermostat called for heat. I heard from the guy this week, he said its still working well.
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Hhhmmm... so if the zone valves literally take a minute to close, I'm afraid that won't stop our problem here. :( It's really just a matter of moments between the thermostat clicking off and the water coming out the top of the furnace.
juddspaintballs link to the exchangers cost less than I anticipated, so maybe the exchanger approach isn't as costly as I assumed. Not that this thing hasn't cost us plenty already... but we need to get it finished and fully functional.
What bugs me now, too, is that I wonder how much of what we spent building it the way it was originally spec'd is now overkill and wasted money. Maybe none of it. I'm not sure.
But we've got 15 (probably 14 in use - not sure why I said 18 earlier... my mistake) radiators in our house that, when spec'd ten or more years ago for the propane steam boiler, yielded a boiler rated at 171,000 BTU. Our Heatmor, I think, is around 200K (optimally). Both the old steam boiler and the new Heatmor, even as it is functioning currently, warm the house up just fine. The radiators are damn hot to the touch when things are cranking.
So we've got two 1.25" PEX lines and a pair of pumps coming into the basement now. That's a pretty hefty volume of water. Would we keep that system in place as-is, add an exchanger and another pump or two for the new house side and more or less be done? Any ballpark estimates on the cost of equipment for that?
Would there be any considerable drop in efficiency or heat loss in this exchanger system vs. what we have now with the water piping through the whole house?
Finally - does anyone think it's realistic to get a system like ours functioning properly outside of using the exchanger? Does it seem like we're definitely look at one or more impossible to find air leaks?
Thanks again to everyone!
- Aaron
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If you have a air leak it should drain back at the furnace all the time. Its not like the air only leaks into the system when the pumps are running. If the air is leaking all the time the water will have to go somewhere.
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yoderheating:
Is your reply suggesting my problem might not be an air leak? Or that the leak situation is I inescapable and I need an exchanger?
Thanks!
- Aaron
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It could well be leaking air into the system all the time and the pumps might just be overcoming the water rushing back down the hill in the return lines via gravity during pumping. In a way, that would actually be reducing the head pressure and allowing the pumps to work with a little less effort.
Halfpress, you could go with one large shell and tub exchanger rated for 200k btu's (same website I linked earlier) and just Tee both 1.25" lines into it. You would keep your existing pumps to pump both 1.25" PEX lines and rather than connecting the supply and return pex lines to your Heatmor, connect them to the exchanger. Run the other side of the exchanger to the Heatmor and use a small pump to circulate that water (Taco 007 is cheap at around $60). The only reason I didn't recommend a flat plate heat exchanger is because you're moving such a large volume of water and I don't believe the flat plates will handle that much water flowing through them all the time.
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I have a hard time believing a air leak would cause drain down only when the pumps are running and the system is under a little pressure. If you had a air leak I would think the problem would continue after the pumps were stopped. Why would you have a sudden air leak and resulting water loss only when the pump shuts off but at no other time? That being said I have never installed a Heatmor and don't understand the bladder system completely. I would love to see what others think on this.
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after thinking long on this problem i thnk (yonders suggestion) of isolating the old house system form the OWB is the best route for you to go. first i would isolate the two systems and do a pressure check on your house sytsem (i take it that it was a closed pressurized system in the past) if this system holds pressure you have no leaks and in fact the water loss was bleed out do to siphoning at the furnace when pumps were off
if this is also true than to seperate the systems with an exchanger is what needs to be done
as for the size of your exhanger measure all your rads into square feet and multiply x 150 (this is how many btu per hour your rads can produce with 170 degree water) if this was a steam system in the past then multiply by 170 to give you the maximum amount of btus your old system could produce.
if your pump is sending water to your exchanger at the rate of 10 gpm and your water is 170 you will be delivering about 100000 btu per hour to the home with a delta of about 20 degrees, as long as your total square footage of the rads does not excede this you should be fine (you did say earlier that the home did heat well)
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Willie, Judd and Yoder:
Many thanks for all the feedback. I am definitely leaning toward doing the exchanger. I've already asked my dealer to price out the parts with that design in mind.
I know my pumps are Grundfos XL models with three speeds. I'm currently running them on low. They are natively 1.25" inlets and outlets to match our PEX supplies and returns.
So I'd have these two pumps running the supplies from the furnace into the house to the exchanger(s). I'd have another new pump or two on the house side after the exchanger to circulate through the radiators.
Are there any other key parts? Pressure tanks of any sort? It's supposedly a closed system, so I don't guess I need any kind of automatic low-water feeder like our propane steam boiler used.
The old steam furnace we had was rated at 171,000 BTU and could heat you out of the house. The 200CSS is supposedly a 200,000 BTU unit (under, I suppose, optimal conditions). So I figure if we get into that 170,000 - 200,000 BTU range on the exchanger(s) we'll be good to go.
Is there any significant loss of efficiency in the exchanger approach vs. our original attempts here for direct, whole-house circulation? Possibly any increases in efficiency? I want to know if introducing this intermediate element into the system is costing us any real loss of heat transfer from furnace to house in the grand scheme of things.
Finally, we'd be mounting this system in our, uninhabitable, hellish dungeon of a basement where the furnace lines come into the house. Does the exchanger get mounted in any kind of special insulated housing? If not, does it make sense to build a housing for it full of R13 fiberglass insulation or some such thing? I'm planning to foam-wrap all of the accessible under-house radiator lines, too, to keep as much heat in the system as possible and out of the basement where nothing would benefit but critters. :)
Thanks again!
- Aaron
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So I'd have these two pumps running the supplies from the furnace into the house to the exchanger(s). I'd have another new pump or two on the house side after the exchanger to circulate through the radiators.
Are there any other key parts? Pressure tanks of any sort? It's supposedly a closed system, so I don't guess I need any kind of automatic low-water feeder like our propane steam boiler used.
If you're doing the heat exchanger in the basement, I'd imagine your pumps you currently have might be big enough to put one on one side of the exchanger (moving water from the furnace) and the other on the other side of the exchanger moving water through the house. You'd have to look up Grunfos's pump tables and calculate your head for each side, but if two pumps can pump the entire circuit, one pump is probably big enough to pump half the circuit and the other pump big enough to pump the other half.
I think you will need a small expansion tank on the closed circuit side (house). I'm not familiar enough with closed systems to tell you whether you need an automatic water feeder...but I don't see how one could hurt either.
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For that many radiators I would recommend a 35 or 40 gal expansion tank, that may be a little over sized but for something like this you don't want to under size it. Make sure you get one that is rated for hot water. A automatic water fill would be nice.
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And yes, if you insulate the heat exchanger, that would be ideal. There would be little to no loss using the exchanger route.
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Quick followup to, again, thank everyone and to say that we're likely going to pursue the exchanger design.
I'm also going to give the pipe network feeding the radiators a good hard look again and make sure there are no loops or other oddities in relation to how our two pumps and the associated feeds and returns interact. I have indications the two pumps aren't serving two isolated loops of radiators (water into one feed with a hose dumps water out of both returns once the system is full)... so I just want to rule out that causing headaches.
HOWEVER, for some freakin' reason, things are working very well right now. I had valved off two radiators that are not bleedable (no bleeder valves and not feasible to install them) and then topped off the furnace sometime last week. I witnessed it blowing water out the top when the pumps stop (as described in my earlier posts) and the bladder ultimately going flat. Nothing had changed, basically.
A few days later, I topped it off again just for good measure. Since that time, it's been working beautifully by all indications. I don't know what changed. The main indicator, though, is that the bladder has stopped going flat for the first time... it gets thinner when the water temp is lower and the pumps are running, but gets quite full (but not rigid) when the water is hot and not circulating. Previously it would be totally flat no matter what within about 24 hours. This has been almost a week now.
The only things that seem different are that those radiators are valved off... but they were between the last two fills and only the most recent time around has seemed to work... and the wood I am burning has changed.
I was initially working from a supply of fireplace-sized, VERY seasoned split oak and some semi-seasoned ash from a tree we had to drop this autumn (been dead a few years). I was going through this wood like crazy, as you'd imagine: very dry, small, split (lots of surface area). So it made hot fires and heated up the furnace fast, but was eating wood like mad.
I got a huge load of enormous, greener oak logs. They, too, are split - but only to the point of making them manageable (and even some of those are a stretch). It's a real workout getting them in the furnace, but it has me down to two loadings a day and I'm no longer seeing overtemp issues. I hope my next load can be unsplit 6-8" logs... working on that.
Again, I don't see how the wood would have a real impact here unless something about the overall heat has an influence.
Keep ya posted!
- Aaron
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My Heatmor has been acting up lately and boiling over. I've traced the problem down to a sticking flapper over the blower motor's output. You might want to take your blower off and clean that flapper. Maybe follow my thread too:
http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=780.msg5076#msg5076 (http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=780.msg5076#msg5076)