Heatmaster G4000 or G7000

[Catawba]

Hey Folks:

Earlier this week upgraded my old Heatmaster MF5000 to a G7000. I am heating a 2000 square foot 1940's two story brick farm house, ductwork is in the basement so I guess that makes it 3000. I live in the mountains of southwest Virginia, 2400 ft elevation. I would say our winters are about like central Pennsylvania due to the elevation, and extremely windy. I was burning about 10 cords from late October to late April on my old boiler. The house is poorly insulated, with none in the walls, and pretty crappy windows. Im hoping to heat a hot tub with the boiler in near future.

Some boiler specs
G7000
8-hour burn rate: 130k btu/hour
Water capacity: 234 gallon
Approx heating space: 7K square feet

G4000
8 hour burn rate: 68k btu/hour
water capacity: 116 gallon
Approx heating space: 4k square feet

I felt like I was right on the line between the G4000 and G7000, considering the poor insulation. The dealer said the G4000 would work fine, but if I was okay with the price difference I might be happier with the 7000 on account of the bigger firebox and longer burn times. I certainly appreciate the ability to have more flexibility in wood length. I got a second opinion from a dealer in another state and he advised going for the 7000 too.


Anyway, Ive had the G7000 for a few days and it is an amazing machine. Im just worried that I really did oversize it, and I am going to be plagued with excessive idling, fires going out, creosote buildup, and reduced efficiency. Did I screw up? Im sure if I got the 4000 I would be second guessing myself too, that's just how it goes. I found another forum thread where someone asked a similar question and the near-consensus was "get the bigger one!" Do you all agree?

 

[sloeffle]

I'd have gone with the G4000, the G7000 is too big for what you are heating. During a cold snap, I think the G7000 might be a better pick, but it doesn't seem like we get those that often anymore. You are better off pushing a smaller boiler harder vs having a larger boiler slumber along when it comes to gasification boilers. They are creosote factories, and a bigger boiler is just going to idle more and create more creosote. The milk has already been spilled so I guess you'll have to live with your decision at this point.

Put enough wood in the boiler for 12 hours and make sure that your wood <25%MC and you'll be happy with the boiler. I've had mine for three winters and all of the problem's I've had have been self-educed.

 

[brenndatomu]

Anyway, Ive had the G7000 for a few days and it is an amazing machine. Im just worried that I really did oversize it, and I am going to be plagued with excessive idling, fires going out, creosote buildup, and reduced efficiency. Did I screw up? Im sure if I got the 4000 I would be second guessing myself too, that's just how it goes. I found another forum thread where someone asked a similar question and the near-consensus was "get the bigger one!" Do you all agree?

Given your heating load in VA, a G4000 would have been plenty...gassers don't like to idle, they like to work hard. Everyone I know that has one says that they seem to use LESS wood during real cold weather (high load) My folks put in a G10000 to heat 2 houses and 2 shops on the family farm...its overkill about 98% of the time, even in NE OH.
Like @sloeffle said, only load enough DRY wood so that it is mostly gone in 12 hours, just enough left to leave a nice coal bed. It'll take a bit to learn what how much wood that 12-hour load is exactly, under various weather conditions.

 

[salecker]

You could add storage to your system and then really get the benefit of your large boiler.
You save some wood usage plus then you can time your burns to when is convenient to you.

 

[sloeffle]

These aren't batch burn boilers. These boilers are designed to idle down and then fire back up when the water gets below the set point you have set in the computer / PLC. All of the settings to idle down and be completely smokeless are part of the PLC program.

I've loaded my boiler for 24 - 36 hours more than once. The 12-hour loadings are just a general guideline, so the boiler has time "dry out" between loadings.

 

[salecker]

No reason you couldn't batch burn
It will still run more efficiently wide open.

 

[sloeffle]

I'm not sure why you'd spend the extra money on tank(s), pump(s) etc to batch burn when the boiler is NOT designed to run that way. And you are also causing more metal fatigue to the boiler itself.

As I said in my last post, the boiler IS designed to ramp up, and down. These boilers have a computer that does this for them. These boilers are as high tech as you can get, that's why they are more efficient than any batch based wood boiler according to the EPA test results. But hey, whatever floats your boat !

 

[salecker]

My opinion and i emphasize My opinion is that storage would still give you more flexibility on when you burn.
And also be more efficient as there is zero idle
As to cost, that is up to the person.My storage just cost me my time and spray on insulation so around $200 bucks for 1000 gallons, no extra pumps on my system.
Not sure on how batch burning would cause extra stress on the boiler metal?
Care to share your opinion on the statement?
Thanks

 

[sloeffle]

Took some metallurgy classes in college and we had to heat metal rods up and dunk them in cold water, oil (there’s a good story there) or let it cool down in sand, wood ash or just naturally and then look at it under a microscope. Metal that was subject rapid heating and cooling developed more stress cracks. No doubt you aren’t rapidly heating and cooling the boiler but you are heating it and cooling it when batch burning. My boiler stay >140F for months straight.

A few article talking about thermal fatigue from heating and cooling:

Thermal Fatigue - Metal Fatigue Life Prediction

High Temperature Fatigue; Thermo-mechanical Fatigue (TMF); Materials at Elevated Temperatures.

fatigue-life.com

https://www.sciencedirect.com/topics/materials-science/thermal-fatigue#:~:text=Thermal%20fatigue%20is%20a%20fatigue,ductility%20rather%20than%20material%20strength.

 

[sloeffle]

Took some metallurgy classes in college and we had to heat metal rods up and dunk it in cold water, oil (there’s a good story there) or let it cool down in sand, wood ash or just naturally and then look at it under a microscope. Metal that was subject rapid heating and cooling developed more stress cracks. No doubt you aren’t rapidly heating and cooling the boiler but you are heating it and cooling it when batch burning. My boiler stays at >140F for months straight.

A few articles talking about thermal fatigue from heating and cooling:

Thermal Fatigue - Metal Fatigue Life Prediction

High Temperature Fatigue; Thermo-mechanical Fatigue (TMF); Materials at Elevated Temperatures.

fatigue-life.com

https://www.sciencedirect.com/topics/materials-science/thermal-fatigue#:~:text=Thermal%20fatigue%20is%20a%20fatigue,ductility%20rather%20than%20material%20strength.

 

[salecker]

Took some metallurgy classes in college and we had to heat metal rods up and dunk them in cold water, oil (there’s a good story there) or let it cool down in sand, wood ash or just naturally and then look at it under a microscope. Metal that was subject rapid heating and cooling developed more stress cracks. No doubt you aren’t rapidly heating and cooling the boiler but you are heating it and cooling it when batch burning. My boiler stay >140F for months straight.

A few article talking about thermal fatigue from heating and cooling:

Thermal Fatigue - Metal Fatigue Life Prediction

High Temperature Fatigue; Thermo-mechanical Fatigue (TMF); Materials at Elevated Temperatures.

fatigue-life.com

https://www.sciencedirect.com/topics/materials-science/thermal-fatigue#:~:text=Thermal%20fatigue%20is%20a%20fatigue,ductility%20rather%20than%20material%20strength.

My boiler stays warm after the batch burn, which is an issue as the controller will keep the fan running as the boiler does not cool down, It never drops below 100F till the season ends

 

[brenndatomu]

My boiler stays warm after the batch burn, which is an issue as the controller will keep the fan running as the boiler does not cool down, It never drops below 100F till the season ends

The firebox steel however is swinging from 100* (or whatever) to well over 1000* with each fire...better than from ambient temp, but not a lot

 

[sloeffle]

Dave,

There’s a site you sent me a few years ago that has splitter parts. What is that?

Think I might bite the bullet and get a bigger pump. After seeing that fast splitter at Walt’s I think it’s with the $$ to change the one out I have.