Cleaning heat exchanger? Something else?

[themaddhatter]

Dealing with a bit of a situation with my OWB setup:

- Have feed lines coming into house into Grundfos pump
- House heated with exchanger in plenum above regular forced air furnace
- Setup has been this way for many years
- Recently, house has not been heating well. Right now, OWB is at 175 F, and inside house is 64 (set at 75)
- Measured inlet and outlet temps of exchanger with non-contact thermometer, and only seeing ~ 40 F temperature drop.

That doesn't seem like much of a drop. Plus, the fan has been set to "ON" for a few days (and is turning).

Do I have a clogged exchanger? If so, how do I go about servicing it?

The exchanger itself can be pulled from the plenum, as it has threaded unions on the inlet/outlet.

Are there options regarding bringing it somewhere to blow the crap out of the tubes?

Also, any recommendations on exchangers to possibly replace?

Throw out any other thoughts...

Thanks in advance,

Shane

 

[Iska3]

Shane, Is the 40 degree drop in themp on the inlet side of the exchanger or the return side? 40 degrees seems like a lot to me. I have something like 15 to 20 degrees drop at the air to water exchanger and 10 degrees at my 10 plate before that if I wash clothes or fill the bathtub. But that temp at the 10 place goes right back up when I don't use hot water.

I have a big old farm house with very little insulation and if my water temp goes below 160 when it gets around 5 above (like last night) my fan will run a lot. Today I let my OWB get down to 125 so I could burn up some of the coals and I could still keep my house at 72. If everything worked well in the past then check the temps on your exchanger for a difference in temp. Do you have a Y screen on your incoming line? That could be clogged. If you have a partial clogged exchanger, it could be that your furnace fan cools off the water faster then it could heat your house. Can you back flush your exchanger? I’d try that first. Did you run your water low? Air in your lines? If not, it is either your exchanger or the pump. What is your pressure on your water lines?

If you have a constant temp of 170 or better at the exchanger and a 40 degrees drop on the return line, I would be taking off my exchanger and soaking it over night or at least blow though it to make sure it was open. Can you hook up a garden house and try to back flush it? If the temp drops on the incoming side then it could be the pump.

 

[themaddhatter]

Iska3,

Measuring the inlet and outlet of the HX is the temp drop (more around 30ish) using a laser thermometer on the copper drops.

Yesterday I pushed water through the exchanger (turned off flow @ stove, and hooked garden hose before pump) and ran that for a couple minutes. Thought it did it, but house is still 66 (furnace is set at 65, so stove isn't doing squat).

It is hard to say if it was all working well before (long story)

System:

-Previous homeowner made "system" including stove build
-Been here 5 years and had issues every year
-This fall trenched and replaced PEX run for stove (PO used crappy PEX and "insulated" with a box of pink insulation - poor insulation & split underground). Clamshell foam insulation inside corrugated pipe (no melt on snow, as opposed to previous years).
-Had Taco 007 pump on system that was seized. Pulled Grundfos UPS15-58 from other (dead) circuit and swapped out (intake/discharge both vertically oriented)
-Pump is ~ 2' below stove bottom in basement, pumps up ~ 4', over 4', down 4', through HX, up 4', over', down 4', back out to stove (~ 65')
-HX is 19"x20"x4" in plenum on top of furnace
-No strainer on system
-No way to measure pressure
-Started system in beginning of December, and seemed to be doing a good job, then a couple days ago, it was windy, and stove got hot (stove door leaks due to being crappy homemade job). Bled water from feed before pump, and added cold water on return side
-Since that point, hasn't been the same

I think it is either air in HX, debris in HX, or weak pump. I did pull the pump, and it runs in my hand, but I can't tell you if it is really pushing anything.

The way it is plumbed right now, I can push household water in before the pump, or I can pull the pump and backflush the HX from the return side.

Should I put a fill connect in on the supply side after the pump?

How can I tell if that Grundfos is moving enough water?

I filled the stove last night, and it still has wood in it, is a 180, and the house is still at 66.

Any thoughts will be greatly appreciated.

 

[Iska3]

Shane, I sent you a PM.

 

[hondaracer2oo4]

Sounds like you have air trapped possibly. Any way that you can point the IR thermometer at different sections of the HX fins to see if there is a difference in temp. The area with the air trapped would show a significant difference. Not knowing what your temp drop was before doesn't help to much with diagnosing with the current results. Only other thing I can think of that could have changed is you could have overheated the pump and its not pumping the gpm like it should but with the temp drop around 30 degree I wouldn't think that it is the issue. I would try to introduce water through your fill flowing it both ways if you can by turning off the shut off first on the outlet side of the stove then on the inlet side of the stove to force water each way.

 

[themaddhatter]

Thanks guys,

I have an email into Isak3 and am on my way to the hardware store for some provisions (after reviewing some nice pics of his setup).

Looking over the system, there are some things the PO may have done incorrectly. And I say that with some sarcasm, as a lot of what he did on this place was incorrect...

I may be putting a new run of copper in to the heat exchanger, as he buried it in the ceiling (highest point) and I can't get a bleeder up there behind drywall.

And looking at the valves he has, I think he MAY have it piped so that the feed is coming into the bottom of the exchanger, rather than the top. Hard to trace, as again, it all goes behind drywall :bang:

So by running that, putting in a couple traps and taps to bleed/drain/fill, I believe I will have something I can work with.

Couple of questions:

- Y strainers: thinking one on the feed before the pump, and one on return before PEX. Good enough? Too much? Preference on vertical vs horizontal orientation? I can do the feed one either way, but would be hard pressed to do a horizontal on the return one.

- Bringing the OWB out of service: I am going to stage and prep as much of this as I can before actual shutdown, but I will need to disconnect the service for a period of time (hoping no more than 2 hours). The OWB is at 180 right now with a little wood in it. I am going to turn off the damper solenoid before I go run around and buy stuff so that should help cool it down some. I can close the valves at the stove, but what I want to know is if I should drain some water down from the system, or leave it full? Should I need to completely kill any combustion in the stove for that short of a shut-down?

Off to Fleet Farm/Menards/etc....

 

[hondaracer2oo4]

I would only go with 1 y strainer if I were you, no need to put two on the same line, nothing should make it passed the first one. Are you asking if you should drain down the water and add some cold? Because if you just drain down the water without introducing any cold water, the water will heat up faster then if you left all of it. I would say that if you have shut the stove down you should be fine with a smoldering fire, it shouldn't put off enough heat to raise the temp to boiling. Yes you are on the right track if you plan to make the incoming heat line from the boiler go through the HX on the output side of the HX first then to the intake side of the HX before it heads back to the boiler. That will mean that the hottest water is on the discharge side of the HX instead of the lower temp water returning to the boiler on the HX discharge which would cool the air down from where it just came from. As far as Y strainer orientation I have not a clue. Follow what the directions recommend.

 

[hondaracer2oo4]

Any update?

 

[themaddhatter]

Any update?

Have a whole mess of parts, and going to start tearing into it soon.

6 hours of parts running and I am ready to take a nap...

Sometimes it sucks living far away from everything.

Might start laying out stuff tonight, and tear whole hog into it in the morning (sun is going to set in a half hour or so). That way I can make sure I didn't forget anything (but I always do, no matter how diligent the effort)

Supposed to be in the 40s tomorrow, so not to worried about system being offline then.

Turned off damper solenoid before I left, came home and it is still smoking, so that should be fine (might take a peak at temps and put in a couple little pieces)

Iska, I bought some door gasket too (I measured it at 5/8" but it is pretty crusty and bad, so I got both 5/8 and 3/4 - one should work in there).

Bleeder valves, copper, y strainers, nipples, tees, spigots and ball valves - OH MY!

At the very least, I will have it at a point where things will be much more serviceable, bypass-able (is that a word??) and bleed-able (again with the wordsmithing).

Thanks for the info (especially Iska - BIG HELP!)

Will post tomorrow (good/bad/ugly)

 

[themaddhatter]

Alright hopefully one last question

I am going to install bleeder ball valves in the return side from the exchanger. The copper right now runs up the wall, in the ceiling, and back down to the unit. Do I have to put the bleeder on the copper return in the ceiling, or if I put a bleeder above the HX before it hits the ceiling, and have a spigot on the other side of the drop to release air, will that suffice?

As I see it, if the bleeder is above the HX, you should be able to get the air out of it, and by having the spigot on the other end of the return, you can keep that cracked when you open the bleeder ball valve to push the air in the copper along the ceiling out. Plus, the spigot will give me a point to apply water to backflush.

I can put the bleeder in the ceiling, but I guess I am just concerned about bleeding hot water above my head :msp_scared:

I do have enough copper to rerun the sets that are buried behind drywall in the ceiling if need be.

 

[TermiteBuffet]

Imho, the hx is working due to the differential in temp.. i think you have a low flow issue , whether it is a weak/ bad pump or a kinked line or a valve on the back of the stove that broke when you operated them. if the coil is below the stove water level it would be hard to trap air with any kind of flow at all.If the coil is above the water level in the stove you need a bleed . Best of luck :smile2: Termite

 

[cckemm]

How much higher or lower is the OWB compared to the pump that (if I read correctly) is inside the house.

Generally when we did OWB installs we put the pump right at the wood stove pulling water from the bottom of the OWB. This was for 2 reasons, being an open system we were pretty much assured that there would be water available for the pump and with running high temperature water at pretty much no pressure we had much less chance of pump cavitation by putting the pump there.

If your pump is inside the house, trying to pull 180 degree water in through your underground pipes, it can certainly be cavatating and that will cause a low flow situation.

Also: non contact thermometers have a hard time reading off of shiny things like copper pipes and galvanized metal, try putting a piece of masking tape on the pipe and read it there.

I would also check the temperature of the pipe right where it leaves the stove, where it comes into the house, where it leaves the house, and where it goes back into the stove. See if you are losing a lot in that circuit. Generally problems there can be overcome with more flow, bigger pump, but if you are making the snow melt that is never a good thing.

If things are set up correctly on an open system the pump should be able to push all the air through they system and back out to the OWB pretty quick.

That is all I can think of quick off the top of my head without seeing what you have there, keep us updated on how things go.

 

[themaddhatter]

Pump is in the basement, ~ 4' below the stove return. Pump location and OWB is same as was installed 15 years ago.

First thing I did this morning was close the return at the OWB, and opened the spigot I have on a tee with the return PEX. Pushed water through the system, and did hear some knocking (assume air).

Next, I turned off both feed and return valves at the OWB, then I took a look at the pump.

I hooked a hose to the bottom of the pump (have a spigot on a tee where the feed PEX comes in) with the end of the hose in a bucket of water and turned it on. It did not draw water. Do circulator pumps NOT draw water? I popped off the pump and opened it up. Pump spins the impeller, so it seems functional. It seemed to move water in the first scenario...

Just want to know if circulator pumps by design require water being pushed into it.

Am going to start plumbing after breakfast.

 

[cckemm]

Just want to know if circulator pumps by design require water being pushed into it.

Circulators move water by creating a difference in pressure, depending where they are put in a system they will either create additional pressure on the outlet side or vacuum on the inlet side or a combination of both. There is a point of no pressure change in every system and with an open no pressure OWB system that point is the OWB. The closer you get the inlet of the pump to the OWB the less vacuum you will create on the inlet of the pump.

Why does all that matter so much? The boiling point of water is 212 F and it flashes to vapor, if you take the pressure on to the negative side that temperature required to boil water starts coming down. Apply enough vacuum and you can get water to boil at below 100 F.

A pump can only pump water, it cannot pump vapor. They are not self priming, if it is not full of water it will not pump. If you are hearing water sloshing around, crackling, popping or anything of that sort from your circulator pump, and you are pretty sure you purged all the air out of the system, you are most likely cavatating the pump (the water is flashing to vapor as it enters the vanes, and then collapses back into liquid at it nears the outside edges of the vanes where the pressure increases). Cavatation can destroy the impeller on the pump, if you pull it out and it looks like somebody sandblasted it, you are most likely getting cavatation.

Sorry this is one of those things that is so simple that it becomes terribly complicated. Nothing beats a properly sized pump installed in the correct place in a system.

 

[themaddhatter]

So, yes, it needs water to pump

It seems to push water through the system alright. Like I said, in scenario 1 it was pulling water from the stove and pumping it through the system and out a spigot.

Just wanted to know for diagnostics.

If I were to say anything about my pump, I would like to go to the next model up. Pump doesn't make crackling noises unless I restrict flow into it.

Like I said, the stove height and pump height have remained constant for 15 years. The size PEX has remained constant for 15 years. I think it is getting the water delivered to it adequately. Now whether I should step up from a Grundfos 15-58 to a 26-99, that is a different question...

Going to install a couple of tees and try to do some backflushing, along with y-strainer for debris.

 

[hondaracer2oo4]

The noise you hear from the pump when you close down that valve is the pump cavitating. Some people describe it as sounding like you have gravel in the pump. Still would like to know what the inlet and outlet temps on the hx are as well as what temp air is coming out of the hx. My air temp at the closest grate is 170. Also if you could somehow easily remove the return line off of the boiler and see how many gpm you are getting. Something changed after you played around with stuff before so it seems as though we should be able to track it back.

 

[Iska3]

-Had Taco 007 pump on system that was seized. Pulled Grundfos UPS15-58 from other (dead) circuit and swapped out (intake/discharge both vertically oriented)
-Pump is ~ 2' below stove bottom in basement, pumps up ~ 4', over 4', down 4', through HX, up 4', over', down 4', back out to stove (~ 65')
-HX is 19"x20"x4" in plenum on top of furnace
[/COLOR

Did the system work good after you changed the pump? Something don't seem right.

 

[mtfallsmikey]

Circulators move water by creating a difference in pressure, depending where they are put in a system they will either create additional pressure on the outlet side or vacuum on the inlet side or a combination of both. There is a point of no pressure change in every system and with an open no pressure OWB system that point is the OWB. The closer you get the inlet of the pump to the OWB the less vacuum you will create on the inlet of the pump.

Why does all that matter so much? The boiling point of water is 212 F and it flashes to vapor, if you take the pressure on to the negative side that temperature required to boil water starts coming down. Apply enough vacuum and you can get water to boil at below 100 F.

A pump can only pump water, it cannot pump vapor. They are not self priming, if it is not full of water it will not pump. If you are hearing water sloshing around, crackling, popping or anything of that sort from your circulator pump, and you are pretty sure you purged all the air out of the system, you are most likely cavatating the pump (the water is flashing to vapor as it enters the vanes, and then collapses back into liquid at it nears the outside edges of the vanes where the pressure increases). Cavatation can destroy the impeller on the pump, if you pull it out and it looks like somebody sandblasted it, you are most likely getting cavatation.

Sorry this is one of those things that is so simple that it becomes terribly complicated. Nothing beats a properly sized pump installed in the correct place in a system.

+1

This was discussed in another thread, with a closed system the circ. is actually just"circulating" vs. "pushing" the water (against pipe, fittings, HX's, thus the term head pressure). Get that pump mounted right at the supply outlet of the OWB. Also, do not ever "deadhead" a circ. pump, with a valve ahead of it shut off. Results can be explosive, ask me how I know...

 

[themaddhatter]

Update:

Long day yesterday, redid several things (based on supplied photos in PM from Iska (thanks again)

- First, flow was incorrect through exchanger. I had assumed (and we know where that gets us) that the PO plumed it right. Yeah.... So redid how the flow goes through (in through top, out through bottom)
- Second, I disconnected a Modine he plumbed in series to put heat in basement. Put manifolds on feed and return to control individual units (still have to connect Modine to manifold, but just wanted to get things flowing)
- Installed y strainer (to help clean stuff out)
- Added spigots with ball valves on manifolds to allow forward and backward flushing
- Removed couple remaining gate valves from PO and put in bleeder ball vales (system is now gate free - God I hate gate valves)

Got everything plumbed, and dealt with a couple leaks (an extra turn here and there on pipes). Forward flushed then backward flushed all in-house with house water, and saw a good bit of sediment and air pulsing blow out. Did 2x until I had 5 gallons worth of clean and laminar flow. Opened feed and return at OWB, and bled air on feed side to pump. While keeping the return closed in the house, opened spigot on return side, saw laminar flow. Plugged in circ pump, and saw increase in flowrate (pump is moving water just fine). Opened return in house, and heard a little bit of water knock for about 2 seconds, then silence... I think I have got it licked now Came up from the basement, and it was 12:30. No wonder I was tired.

As soon as sun came up, put a new gasket on door (needed it), started a fire, and we will see how it heats things up today.

Observations:

- Was a couple of unions on heat exchanger to allow for pulling unit. PO had done a piss-poor job doing the solder job, and slobbered solder on the face of the union (part where threaded nut presses against), creating a wobbly union. His remedy for this was to tighten the unions using the power of Odin or something, because I had to put a little heat on the nuts to get them loose. And he recta-sealed the threads :bang: Always been told to NEVER put sealant on union threads. If the seat is done right, should only need to be threaded on and tightened. So, I heated up the union and cleaned off his ancient cruddy solder off the face and wiped it down. Cleaned as much recta as I could, and seats well now without leaks.

- Definite improvement in purging/flushing/backflush capability by doing spigots on both sides with manifolds.

- OWB held a BUNCH of heat during the downtime. Valves closed in the morning, with stove at 140. No wood had been put in for 24 hours, and even then was only like 4 pieces ~ 6" in diameter. Left the power on to the damper to burn anything left in there. At 11 pm when I opened the valves, and the stove was STILL at 140! I was totally shocked with that. Was a mild and wind-free day (high was ~ 40 F). Good example of insulation, thermal mass and residual burn I guess.

- I am going to have to do a mid-season door replacement This door is totally FUBAR. The PO actually built the OWB, and for the most part, he did a decent enough job. I did have to fix a floor leak in it 3 years ago, but that on a system that he built 15 years before I moved in, so that is about 20 years old. The weak spot was by far his door design. The door has a welded piano hinge along one side that is welded to the door and the throat into the firebox. The throat sticks out ~ 2" proud of corrugated steel shell of the OWB. he designed the door to recess around the outside of the throat. Well, the piano hinge started binding this fall, and even though I PB-blasted the hell out of it and hosed spray oil into all the points I could get to, the binding continued, until his tack welds (yes, tack welds) along several sections of the door cracked. Now, the bottom third of the piano hinge is connected, but the bound section just folds over, and this bent folded section is right in the gasket seat area. This forces the door to sit crooked, and keeps the door for seating properly. So much so that I often need to use the back side of a splitting maul at the top corner to get the door to seat and latch. I have a pretty good idea of what I will need to do to fabricate a new door and hinge system. It is going to be interesting on the logistics of doing the swap during the heating season. I will be exploring what others have done for door and hinge designs and adapt it for this scenario (may have to start a different thread on that). Will be designing the door to be able to attach to the throat without welding (dragging a 230 line out to the OWB will be difficult at best, and don't have a generator). If the design goes well, I would only have to cut off and grind off the piano hinge, drill some holes for hinges, backing plates, and latch, and reconnect the solenoid for the damper.

Anyways, enough rambling on. Thanks to everyone for the comments, answers, and suggestions. It was greatly appreciated and helpful!

Will post later tonight after stove has been burning for a while on status.

Now to start that door design.....

 

[avason]

air filter

I had the same problem...fan would run in the air handler...but would not run much air. Have you checked the filter. Just happened to me yesterday. Ran all day and it wouldn't heat pastthe right w.ay.. 68. Changed the filter now she's heating