I just received some interesting news today

 
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lsayre
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Post by lsayre » Tue. Jun. 25, 2019 5:36 am

I'm now considering a combination boiler that has two tanks and both heats the house and heats DHW. They make them to hang on a wall like my resistance boiler does. Initially considering the Navien NCB-150E Combi-Boiler. Input is rated at 60,000 BTUH and output is rated at 56,000 BTUH @ Gross, and 49,000 BTUH @ net, but I'm sure those are calculated for condensing efficiency, whereby I've learned that condensing conditions are virtually never achieved in the real world, so I'm ballparking it at more on the order of 51,000 BTUH @ Gross output, and 44,350 BTUH @ Net output in the real world. Plus it has 120,000 BTUH input for on demand DHW. That should be about 104,400 BTUH output at a more real world 87% efficiency, or just about enough to raise 3 GPM flow by 70 degrees.


 
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Post by McGiever » Tue. Jun. 25, 2019 8:26 am

Too bad you couldn't just stuff a burner inside the Coal Gun for cheap and call it done...

 
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Post by Rob R. » Tue. Jun. 25, 2019 8:45 am

lsayre wrote:
Tue. Jun. 25, 2019 5:36 am
I'm now considering a combination boiler that has two tanks and both heats the house and heats DHW.
Why?

 
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lsayre
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Post by lsayre » Tue. Jun. 25, 2019 9:18 am

Rob R. wrote:
Tue. Jun. 25, 2019 8:45 am
Why?
The cost is about the same as a home heating only boiler, and it would not require that I purchase an indirect HWT.

The downside to this which I just realized is that if we ever had to switch over to the resistance boiler as a back-up, it would have no way to heat the homes DHW since there would be no indirect tank.

 
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Post by McGiever » Tue. Jun. 25, 2019 11:06 am

lsayre wrote:
Tue. Jun. 25, 2019 9:18 am
The cost is about the same as a home heating only boiler, and it would not require that I purchase an indirect HWT.

The downside to this which I just realized is that if we ever had to switch over to the resistance boiler as a back-up, it would have no way to heat the homes DHW since there would be no indirect tank.

Didn't know that people used backup sources for their NG fueled heaters????
Even at that, electric would seem an odd choice as a backup to another utility supply.

Some get around buying an indirect by using a plate heat-exchanger for couple hundred bucks...
lsayre wrote:
Mon. Jun. 24, 2019 2:13 pm
Some of the NG boilers I've been looking at have warranties with a fine print disclaimer that the boiler must be installed by a licensed contractor who is approved by the boiler manufacturer or the warranty will be considered void, so I'm leery of doing the install myself, or with assistance.
That's like paying for a big repair before it has every even broken...not much of a warranty at all, unless you are betting it will break big and break often and warrantor just loves to pay out claims all the time...
Last edited by McGiever on Tue. Jun. 25, 2019 11:26 am, edited 1 time in total.

 
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Post by lsayre » Tue. Jun. 25, 2019 11:26 am

McGiever wrote:
Tue. Jun. 25, 2019 11:06 am
Didn't know that people used backup sources for their NG fueled heaters????
Even at that, electric would seem an odd choice as a backup to another utility supply.
The flimsy way they make them these days they are often not built to be very long term reliable. User satisfaction is often terrible.

That said, I think I will jettison the idea of keeping the old resistance boiler. The house was zoned for a "high mass" (high water mass) heating unit, and the hang me on the wall units are very "low mass", so each of my zones feet of HWB's are way too short overall for low mass boilers and will thereby seriously short cycle the boiler. I just calculated that I will need a 20 gallon buffer tank (at least) to satisfactorily resolve the problem of short cycling. The buffer tanks I've looked into so far seem to cost essentially as much as an indirect HWT. I wish there was some way to dual purpose an indirect HWT to both provide for DHW and mitigate short cycling, while still permitting "turn-down" via outdoor reset without getting into a Legionnaires situation.

I could perhaps use the coal gun for the needed extra thermal mass (since it has 23 gallons of water capacity), and also use its coil for DHW, but then I would have to toss out the idea of outdoor reset and turn-down, and maintain the system at about 160 degrees as at present, as I already know that at 150 degrees and below my boilers DHW coil teeters on tepid showers.

 
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Post by McGiever » Tue. Jun. 25, 2019 11:36 am

Please state your objective or goal of your desire for an outdoor reset...they may be met by other means...

And do you have any hydronics reference books presently?


 
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Post by lsayre » Tue. Jun. 25, 2019 11:46 am

McGiever wrote:
Tue. Jun. 25, 2019 11:36 am
Please state your objective or goal of your desire for an outdoor reset...they may be met by other means...

And do you have any hydronics reference books presently?
Outdoor reset has been shown to both bring you into condensing conditions more often and save you money.

I have the internet and the Houlihan books around somewhere.

 
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Post by McGiever » Tue. Jun. 25, 2019 11:59 am

lsayre wrote:
Tue. Jun. 25, 2019 11:46 am
Outdoor reset has been shown to both bring you into condensing conditions more often and save you money.
I understand how that makes for finding a solution tough. Running water temps by controlling or limiting combustion has not many options.

Better save a lot of money and never need much more repair costs or else a non-condensing fuel waster that doesn't break down and runs forever will be the better investment. High Efficiency units put all HVAC contractors kids through college...;)

And guess when/what time of year they will break down???

My point of all this is to show that unit reliability should far outweigh efficiency...bragging rights don't mean squat when it's broke down at 2:00AM on a Sunday and it is a Polar Vortex outside.

 
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Post by lsayre » Tue. Jun. 25, 2019 12:18 pm

McGiever wrote:
Tue. Jun. 25, 2019 11:59 am
I understand how that makes for finding a solution tough. Running water temps by controlling or limiting combustion has not many options.

Better save a lot of money and never need much more repair costs or else a non-condensing fuel waster that doesn't break down and runs forever will be the better investment. High Efficiency units put all HVAC contractors kids through college...;)

And guess when/what time of year they will break down???

My point of all this is to show that unit reliability should far outweigh efficiency...bragging rights don't mean squat when it's broke down at 2:00AM on a Sunday and it is a Polar Vortex outside.
Words of wisdom there. I believe the highest efficiency non-condensing boilers are about 85-87% efficient, and the condensing boilers are "purportedly" 94-96% efficient.

95/86 = 1.105, so at most the non condensing boiler will cost 10.5% more in natural gas to operate (all else being equal). And the real world cost difference will be less because condensing conditions can't always be met, so whenever they are not being met the claimed to be 95% efficient boiler is merely 86-87% efficient.

 
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Post by lsayre » Tue. Jun. 25, 2019 12:44 pm

The Energy Kinetics System 2000 non-condensing NG boiler looks nice, and seems to have honest efficiency ratings, but I just called them and they don't do any business in Ohio. They also will not sell one to anyone who is not an Energy Kinetics trained and certified HVAC contractor. There are zero of such contractors in Ohio per Energy Kinetics.
Last edited by lsayre on Wed. Jun. 26, 2019 7:07 am, edited 1 time in total.

 
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Post by nepacoal » Tue. Jun. 25, 2019 1:31 pm

lsayre wrote:
Tue. Jun. 25, 2019 12:44 pm
The Energy Kinetics System 2000 non-condensing NG boiler looks nice, and seems to have honest efficiency ratings, but I just called them and they don't do any business in Ohio.
Looks like Supplyhouse.com has a pretty decent selection of non-condensing NG boilers...

 
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Post by lsayre » Wed. Jun. 26, 2019 7:02 am

nepacoal wrote:
Tue. Jun. 25, 2019 1:31 pm
Looks like Supplyhouse.com has a pretty decent selection of non-condensing NG boilers...
I spent considerable time perusing these yesterday, and they generally seem to cost more than condensing boilers. And most all of them are similarly low mass boilers with capacities on the order of 1.1 gallons of water. And most are also of much higher input/output BTUH than I need as well.

I read a Minnesota study yesterday which stated that a high efficiency condensing furnace or boiler adds value to a home and increases its likelihood to be sold. Oddly enough, even though the boilers initial cost is similar and may well favor the condensing type, the Minnesota study found that the average cost charged to install a condensing boiler is $2,500 more than the cost to install a non-condensing boiler. There appears to be an HVAC gouge factor at play here. The Minnesota study found that due to this $2500 up-charge, the average time period to begin seeing $$ savings from a condensing boiler over a non-condensing boiler is 23 years. That means the money saved by an average NG condensing boiler is only on the order of about $109 per year. And since they likely use 20% more NG to heat homes in Minnesota than in Ohio, the savings here would be on the order of $87 per year, and break-even would come ~29 years down the road.

Non condensing furnaces and boilers were banned in the EU 11 years ago for use both in existing homes and new construction. It appears that when it comes time to repair or service a non condensing model, it must be replaced instead.

 
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Post by nepacoal » Wed. Jun. 26, 2019 7:32 am

And most all of them are similarly low mass boilers with capacities on the order of 1.1 gallons of water.
Wow, i never looked at NG boilers water capacity. Can't believe it is so low. Even one with a tankless coil only has 3.1 gallons. Seems odd when compared to oil and coal boilers.

 
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Post by McGiever » Wed. Jun. 26, 2019 8:41 am

Could be that low mass design contributes heavily to the functional condensing process...

So, the difficult question is does your NG boiler choice be swayed toward bottom line costs or towards home resell value???
Last edited by McGiever on Wed. Jun. 26, 2019 8:50 am, edited 1 time in total.


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