Outdoor wood boiler pump failures

Gus

I have a Heatmor outdoor boiler heating my home and shop. A pump for each mounted on the low supply side of the boiler. The return is on the high side. I'm going through pump cartridges in each pump every year. Sometimes twice. One of the logical reasons might be air in the system. Do I need some type of bleeder valve? If so where would it/ them go? I'm using soft water and it never gets low. Both pumps have to pump down below ground. The shop line then goes up 10' to the ceiling area. The house line keeps dropping to basement floor level then back up to boiler. The manufacturer is about done giving me new cartridges. So I'm also thinking about a different brand of pump. Any help appreciated. Gus

Tony_23

Need more specifics

But for starters, I think you have the supply and returns reversed. The bottom taps are the returns from the house/garage.

Are your circs outside w/the boiler ? I'd try installing them inside nearer the distribution system(s).

What model boiler and what model circs do you have ? What size pipe to the house/garage ?

hr

A couple issues

Often those outdoor furnaces come with high head circs to move all those BTU through the 1" pipe they recomend

Many of those outdoor units are un-pressurized vessels.

They mount the circs low trying to get some NPSH to prevent cavitation. Grundfos UP series need a minimun (inlet pressure) 1.3 psi at 140 F water, and 4 psi at 190. 15.6 psi at 230F!

The pump could be oversized, even grossly oversized!

Also water quality in an open vessel is questionable, and corrosion common. This too can chew up circs.

Yet another issue is they often boil when over fired. As noted above the higher the fluid temperature the more pressure you need on the circ. If that is a 2 psi boiler the water will go above 212 before it boils over.

Check pump size for the GPM load and head required.


As I recall the Heatmor is sold as a semi pressurized unit. I think it has a 2 lb. iron weight on the top vent of the heater. And some sort of bladder system to accept expansion. The weight keeps some pressure in the drum and acts as a relief of sorts. Keeping it under pressure also helps with the cheicals that need to be added. They don't boil away like on the un-pressurized types

Weird animals those un pressurized outdoor units. especially when all the radiation is at, or below, the level of the water in the heated


hot rod

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Gus

The boiler is labeled supply and return. Pumps are outside with the boiler. Model 200 boiler and 1" pex to house and shop. o11 pumps.

S Ebels

Get used to it

ALL outdoor wood boilers that are set up with 1" tube going to the house will eat circs, and continue to eat circs until you get the correct size piping run into and out of the boiler. That is the only "fix" there is. When we install an ODWB for a customer, the minimum tube size we use is 1 1/4" pex. That is only used for runs under 100' round trip. We typically use a 007 Taco or a 15-58 Grundfos for the circ on the main loop. If the main loop in and out of the house is over 100' we jump to 1 1/2" and if it's over 200 we us 2". Guess what? We haven't had a single pump failure where the water quality has been maintained correctly.

As Hot Rod eluded to in his reply, all circs need a positive pressure at the inlet to avoid cavitation. What these ODWB boiler manufacturers fail to understand is that just because the inlet is flooded, it doesn't mean that there is any pressure there. When you lower the inlet pressure to even a couple water column inches below atmospheric, the water can boil and flash to steam at the inlet. The circ then promptly burns out because they can't pump steam. It's as simple as that.

You shouldn't have gotten me started on this because it's one of my pet peeves. Really tweaks my tail when I read right in the ODWB manual that 1" tube is OK. IT'S NOT!!!! These idiots are recommending 1" tube because it's cheaper, plain and simple. If the system is cheaper then they can sell more of them. There's also the reluctance of a manufacturer to recommend something more expensive for their boiler than any other manufacturer is recommending. If they are truly recommending it because they don't know any better then they should keep their opinions to themselves. Because they are wrong!!
Nearly all of the people we have installed one of these wood eating wonders for have complained like crazy that "No one else says you have to use that size tube", But you know what? They are not burning out $250.00 circs one or two times a winter. Do the math on bigger tube vs a dozen or so circs over the life of the boiler.

Solutions to your problem

A: Install the correct size tube based on total length and a maximum of 3-4 feet of head.

B: Install a strainer on the inlet of the circ and keep it clean.

C. Maintain the correct PH in your boiler water with whatever additives required.

Use the smallest circ you can that will deliver the required flow.

E. If you are running multiple heat emitters in the house, set up your boiler pump as a primary circulator and run secondaries to all the loads.

F: If you are serving multiple buildings, run a separate loop to each one, again using the smallest circ that you can.

Implement those suggestions and you should see 4-5 years life from your circs. If you try to shortcut any of them just buy some stock in whatever company you choose because you WILL continue to fry circs on a regular basis.

Sorry to sound tactless but the truth is sometimes not very delicate.

BTW, I think that the typical installation of any brand ODWB is doing a dis-service to the entire hydronics industry. Many people are having a host of problems with these units becasue of poor installation practices and the HO'S come to believe that all hydronic systems are prone to failure. The real fact of the matter is that if they are installed correctly, they are less trouble than a typical 90% furnace.

I could go on and on and on but tomorrow's a long day.

hr

Steve, what type

of pex are you able to use in 1-1/4" size? What do you run for 1-1/2 and 2" pipe?

I'm thinking of going to copper in the InsulSeal pipe I use.

It's pretty common for first time ODWF folks to over heat them and melt the pex off the connections! Even PAP will melt off it's connections. It's not always an easy fix when the tube is buried in the ground.

I like you answers, except I would not put a y strainer at the inlet to the circ. It further coaxes it toward cavitation especially with the 0011.

I'll bet the 3 speed Grundfos Super Brute would probably get the job done. I'm always suspecious of the output ratings on those outdoor furnaces. I suspect you don't really need to move as much GPM as they claim you do.

Pretty tough to get 200,000 out of an inefficiently burning barrel stove And the pressure drop through the furnaces itself is zip. The distribution piping poses the "bottleneck"

hot rod

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S Ebels

Big Pex

We've been using Rehau and have had no issues with fitting failures. I like their press on sleeves although it's a pain to rent the $5,000 hydraulic tool set everytime we do a job. The fittings do not fail, period.

We use Insulseal also and it is a tough pull through their 4" with 1 1/2" pex. For the 2" we wrap it with LOW-E insulation (foil/foam) then field fab a 2" thick foam "box" and lay the tube in it.

Getting back to the Rehau fittings; We had one pair of tubes get stuck in the middle of about 130' of Insulseal last winter. We couldn't budge it either way with 3 of us yanking on it. Deciding that we couldn't make matters any worse, we tied the pulling rope to the Sprinter's tow hook and gently backed it up. We were pulling so hard the van was spinning but the tube and fittings stayed together just fine. That's a tough fitting!

hr

I can move 200,000 thru

1-1/4' pex if I run a 40 degree delta t. 10 gpm 9 feet per 200 feet of tube. Easy for a small wet rotor circ.

On an upcoming job with a wood boiler running radiant, I may try this. Run the 200 gallon buffer between 140- 180 and sip off my radiant temperature.

These outdoor burners seem like the ideal place to leverage wide delta t. Low returns don't seem to bother them

Although this one is getting a gasification wood boiler. the really like 140 plus return to stay efficient.

I'll look into the Rehau. Is a compression (non tool specfic) fitting available? All I would need is 4 pex to whatever adapters.

I still feel if the Insulseal is all straight run, silver soldered, 20 foot lengths of copper may be an option. Perhaps slide the insulSeal as the copper is soldered from either end. Your thoughts??

hot rod

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Steve Ebels_3

Hot Rod

"These outdoor burners seem like the ideal place to leverage wide delta t. Low returns don't seem to bother them "

They are usually dripping with creosote and tar anyhow so I don't see what additional harm could be done running one at 140 for a radiant app.

"Although this one is getting a gasification wood boiler. the really like 140 plus return to stay efficient."

Same rules apply to ODWB's as to any boiler. The cooler the water is, the more efficient it becomes.

"I'll look into the Rehau. Is a compression (non tool specfic) fitting available? All I would need is 4 pex to whatever adapters. "

I stock fittings for 1 1/4 and 1 1/2 inch and I have a 1 1/4" manual expander and press hand tool that I rent out. The fittings for 1 1/4" will accept 1 1/4" copper on the ID and are 1 1/2" MPT on the OD. Same goes for the 1 1/2" fittings only one size up. The 1 1/2" pex and fittings require the use of the hydraulic kit. Trust me, you need it unles the pex is about 130*. I don't know about a "normal" type fitting, haven't seen on in their catalog.
Let me know if you'd like to try the 1 1/4" tools and fittings and I'll send 'em down with the UPS guy.

"I still feel if the Insulseal is all straight run, silver soldered, 20 foot lengths of copper may be an option. Perhaps slide the insulSeal as the copper is soldered from either end. Your thoughts?? "

Lots of people get bugged about splices of any kind underground but I wonder how many consider the splices in their well pipe or the gas (natural or LP) line that runs to their house. I don't have a problem with it at all. A joint is a joint is a joint. They're either done right or not. The copper wouldn't be a bad idea for someone with more trustworthy soldering skills than I possess. It'd be a bugger to pressure test and then have to deal with a leak. At least with pex, you could pull it back out whereas with CU you'd be in the crapper.

What gasification unit are you playing with?