Maxim 175 efficiency question

[Redngold]

Greetings!

I have joined this forum because it looks like a great place to ask questions.

I am considering the installation of a Maxim 175 boiler.

First some background: I am a dairy farmer in Eastern Ontario where we require heating from mid-October to mid-April with a few weeks of below 0'F during the coldest of winter. We have a 2,400 square foot log house that is over 140 years old. We had an energy assessment done last year, and the house did better than I expected due to new windows/doors and some insulation. We heat with a forced-air oil-fired furnace rated at 130,000 btu's and heat our water with oil. We also have a 30,000 btu propane fireplace, and a Jotul 500 wood stove. The house is not well laid out for heat distribution, as we get too hot in the room with the wood stove, and freeze in the kitchen. We use approximately 1,200 gallons of heating oil per year (furnace and water heater) plus 6-8 face cords of wood and propane. The energy audit recommended a geothermal/solar system.

Three years ago, I purchased a Traeger GBU 130 add-on corn furnace. Unfortunately, our home insurance would not allow it to be installed as an add-on unit to our oil-fired furnace. I then considered a Bixby UBB, but again would not be allowed to tie this unit into the forced-air furnace. I was then told about an Irish boiler: the Woodpecker by Gerkros which looked very interesting. Unfortunately, Gerkros has fallen victim to the credit crisis, and is to be liquidated. I have been recently directed to the Maxim.

I had our local Maxim dealer in to see me, and he recommended placing the unit in our open wood shed. This would allow easy installation to the forced-air furnace and hot water tank. It would also be easy to send a pex line to the barn to heat water in the dairy. I have decided that it would be more economical to install a heat reclaimer in the dairy which would pre-heat water all year, and therefore I will not be heating water in the barn with the Maxim.

My question is: Is the Maxim too big for my purpose?

I would like to get some feedback on this if possible. I presume that the Maxim will run fairly efficiently while we have very cold weather, but what about late-fall early-spring conditions where it can freeze at night but turn mild during the day - will I lose the efficiency while the Maxim idles?

Thanks!

Alan

[jdeere5220]

Redngold-

You are right the unit is not super-efficient if it's on idle a lot. To paraphrase someone else in this forum burning nothing costs less than burning a little. But some things to consider:

You can turn the idle-mode setting down to the point where the auger turns about 1/10 of a turn (about 1/2 second) every 3 minutes. That's pretty darn slow. If that's too slow and the fire goes out, it will auto-relight the next time there is a call for heat.

If you do decide to purchase, I find the M250 unit is just right for me so far, and I have similar loads to what you describe. I think they changed the rating method more than the actually changed the stove and the new model is not much more $$$.

I don't know what the "least you can burn a day" is yet because it's been pretty cold since I installed mine, but I would guess something like 40 lbs pellets or 60 lbs corn (I've found you can't run the corn quite as low or the fire does go out). Maybe ask your dealer, or maybe someone else here knows more about "light load" operation of these units and they can fill us both in.

Anyway if the unit is not doing much you are still going to burn some just to keep a fire going, you are right about that.
_________________
Maxim M250 outdoor corn/pellet burner
Old Beat-up Gravity Box
I support Global Warming

[sting]

Proper sizing directly relates to overall boiler efficiency. Short-cycling (frequent on-off cycles) and the greater shell losses of an oversized boiler can dramatically decrease the efficiency of the heating plant.
_________________
When you turn your boiler on -- Does it return the favor?
I am sorry - My responses are limited - You must ask the right question!

[T_Hartigan]

What did the energy assessment say was the load for the house?

Judging by the amount of heating oil with wood usage, I think it will probably be a pretty good fit. If your insurance is forcing you to an outside unit, and you want to burn corn or pellets, I think the Maxim is one of the better ones out there. Do some research on any unit your looking at.

I am shocked at what the price has gone up to on these units though. The M250 has a much better heat exchanger than the M175.

Since you already burn wood any thoughts in going to a wood gasifier?

Tim
_________________
3rd year with Central Boiler Maxim 175
100% corn first 2 years.
3rd year, Corn, Acorns, 1 ton wood pellets.

[Redngold]

Hello,

Thanks for responding to my question.

The energy assessment returned a figure of 1.3 million btu for the average daily load, which I find a bit high. However, I can see the load being quite a bit larger when the heating degree days exceed 65!

This being the case, I presume that the Maxim 175 would only run at full efficiency approximately 30% of the time, and the Maxim 250 less than 25%. I didn't price the 250 as my dealer seemed to indicate that it was too large for my needs. I enquired about the new E-Classic wood furnace, and was told that it also would be too big for me. I had also considered the Greenwood, but don't really want to heat with wood as our main source (I cut a few cords on the farm every year, but must purchase the rest).

Back to efficiency, Maxim claims over 95% at combustion. Would 85% be a good ballpark efficiency when considering heat transfer to water and transfer to furnace?

Has anyone left the Maxim on idle for a day to see how much corn was burnt?

Alan

[jdeere5220]

Sting-

You frequently refer to how oversizing is bad, and I've read all your posts on the subject, but I'm still left wondering a couple of things:

1) The Maxim is not "ON or OFF", but continuously variable in terms of fuel input speed. For me, peak load is actually higher than 250K BTU, but average load is less than 60K BTU/hr. So most of the time the unit is running at the lower end of it's range. So the auger is turning slower than it can. I'm having a hard time understanding how that is bad.

2) I've done some work to even out my loads, so that my peak demand isn't so high (by adjusting blower fan speed, prioritizing loads, and using a timer). So now my boiler runs more continuously at a more "mid-range". At the end of the day, it really doesn't seem to matter, it's burning about the same amount of corn every day as it did when all my loads came on at once and then the unit sat idle for two hours. I think I need the BTUs I need, and it doesn't matter if I get them all at once or over a longer period of time, requires basically the same amount of corn either way. Any thoughts?
_________________
Maxim M250 outdoor corn/pellet burner
Old Beat-up Gravity Box
I support Global Warming

[sting]

not much you can do

You have what you have - I wouldn't park it for something else now -- the cost of operation doesn't exceed the ROI of something else in your case.

But a boiler will run more efficiently working hard -- Idle fires waste energy - mid capacity fires -IE running at reduced feed rate for log periods will not take advantage of the vessel exchanger capacity and you still have parasitic loss regardless - only now from a larger than necessary boiler, so the loss if a bit more.

Most pellet and corn boilers are not ON/OFF - and those that are have the cost of relighting to add to the mix.

I just got my a$$ handed to me on another forum on this subject as the so called expert was claiming that an oversize boiler was dangerous and prone to burn back. That's just not true with proper management - the management as you describe above reducing feed rates, matching combustion air, keeping a non condensing burn temp, watching that the fuel is not burning rich and soot is not condensing in the fire tubes the fire tubes - but standby loss and burn efficiency are constants. Constants that are exaggerated by an oversize appliance.

Hope that helps to clear things up -- if I missed the mark, please ask exactly whats on your mind
_________________
When you turn your boiler on -- Does it return the favor?
I am sorry - My responses are limited - You must ask the right question!

[whippingwater]

[sting]

[Redngold]

[T_Hartigan]

[Redngold]

[jdeere5220]

[jdeere5220]

An update-

My stirrer (the think on the end of the feed auger that churns up the contents of the burn pot) just basically melted off yesterday. I've read on this forum of others having this problem, but I was hoping it was fixed on the newer units. Guess not

Still overall I'm satisfied with how solid and well-built this unit is, everything else seems first rate. But obviously the stirrer isn't the right type of steel, because only 6 weeks of burning and mine melted and broke off. Guess it can't take the 1200 degree burn pot temps I've been running.

If I have any other issues I'll let you know. These units are too expensive for these sorts of break-downs to happen.
_________________
Maxim M250 outdoor corn/pellet burner
Old Beat-up Gravity Box
I support Global Warming

[Redngold]