Hi:

My new 2400 sq.ft ranch was built in the latter part of '03. I had a Burnham Revolution RV5 installed with taco 007's and slant fin high output baseboard. Turns out my boiler is approx twice the size my home calls for. The plumber based his calculations on the DHW tank which is a 42 gal burnham alliance. He also did not have a heat/loss calculation.

I found out 2 yrs after I moved in and started to get a gas usage history that my heatloss is 48,000btu. A heat/loss calc. was done by the company that did my central air and has been confirmed again. Rbeck was kind enough to come to my home and assess the situation. He advised to install a Taco 2 stage ODR, which I did at a cost of $1300. The past 12 months I used 1050 cu.ft (94 cu.ft) less with the ODR. Thats about a 9% savings. I thought I would save more.

I am now considering installing a Buderus GB142 mod/condensing boiler. I just had it spec'd out (no price yet) and a new heat/loss calc was done at the same time. I will be able to keep just about everything from my prior install (taco's, indirect, expansion tank, etc). There will be minimal piping and a new vent.

While its virtually impossible to calculate how much if any I will save with the Buderus can anyone give me a ballpark figure? The Buderus has the ODR built-in and will be sized correctly. I assume the largest savings will be from the sizing and the modulating/condensing feature. I am also assuming they will suggest the smallest model (24). In addition [zzzzzzzzz sorry, can't sell here... zzzzzzz] Regards...

 

It is unfortunate that your present boiler is vastly oversized but if it is saving money that you want to do then you have to account for the capital costs of the new boiler versus the payback time and the cost of money.

An almost ten percent savings from the ODR is actually pretty good but are you now willing to just toss that $1300. down the drain by buying a new boiler that may only save another 10% of your present heating costs?

Do you currently have the funds for a new boiler just lying around? If not, what interest rate will you need to pay to borrow the money? If you borrow, you have to factor in the interest that you pay on the loan as part of the capital costs of the new boiler.

As wonderful as a lower fuel bill will look if it is offset by higher loan payments then what have your really saved?

 

thanks furd for your post. The most I would pay for the new install is $5k which I have available. If I knew I would save about $400-$500 a yr then I would do it. I should get the estimate within a week.

If the savings is only say $100 a year then its a no brainer not to do it...would take 50 yrs to get my money back on a $5k job. The hard part is trying to figure how much I would save. I don't know if Buderus could calculate that to get a ball park figure. I just hope there are no other issues with the small GB142 like making enough hot water. We are only two here and have never run out except when filling the whirlpool.

Another option is to get the correct size Burnham Revolution and keep the taco 2 stage. that would be an exact piping and wiring replacement. The revolution is an excellent boiler, but looks like the new high tech boilers are of the condensing/modulating type. Everytime a non condensing boiler fires up she's at full blast. regards....

 

The plumber should have stuck to plumbing and not heating. An RV-3 with a large indirect would have spared you from being in this situation and it also would have filled the hot tub. Better to oversize the indirect than the boiler.

That said, the smallest GB142 would only have 66% of the DHW recovery capacity of the RV-5. The gain in efficiency going from a Revolution to a modcon will be less than some others changeovers, yet you'll still be paying for a new boiler and get beat up selling a used boiler. If you move in a year or two for any reason, the selling price of your house won't really change.

Modcons are still quite new in the market and they'll only get better with time, especially on the controls side. The prices will also come done because they use fewer materials. If I were you I'd hold off for a bit.

 

What would it cost to have the correctly sized Revolution dropped in? That would save a considerable amount of labor, and salvage the near plumbing. I'd guess going from the Revolution to a full mod/con would save you the difference between their rated efficiencies, which would only be at most several percent? Plus, the proper sized Revolution would also yield some savings that would have to be added to the equation.

Hard decision!

 

Also factor in the care and feeding required for an aluminum-block mod/con like the GB. Chances are you will need to treat the water even if good city water. Add a few bucks for Rhomar products.... And have it cleaned and checked out annually.... Maybe you save $200-300/yr on fuel (that's a total WAG). You will spend about $100+ of that on the tech and whatever he does. And you are still getting beat up on the old boiler and controls, and the new boiler and controls.

I cannot see a reasonable payback.

Nor do I see a reasonable payback on downsizing the boiler to a smaller Rev.

Buffer tanks are all the rage these days. Maybe consider adding one. It might help, and be far shorter money than the other options.

 

Hi:

Thanks all for your replies. I have a few questions. My new heat/loss calc should be done soon. I am assuming it will be around 45,000btu loss.

If I decide to go to a smaller revolution boiler should I go with an rv3 or rv4? In addition, is it possible to add another 42gal. indirect or can you only use 1 large tank? Is having a larger indirect necessary if I go with a smaller revolution and will that extra tank add to my gas usage woes?

I don't understand how the sizing works. Its seems that you are supposed to size as close to possible to the homes heat loss. But what if, as in my case, you have a very tight house with a very low heat loss. Isn't the boiler possibly too small for the DHW load? And isn't adding another tank (or larger tank) contributing to this problem?

Lastly whats a buffer tank? Regards...

 

Yes, some plumbers size the boiler to the DHW demand. The DHW recovery time will suffer when the boiler is downsized. Your savings may not be that great, the Revolution is a good efficient unit. Energy Kinetics makes one of the most efficient boilers for residential use--they make only one boiler size!

If I were you, I would contact Glen Stanton at Burnham for a professional opinion regarding your situation, once you have your heatloss figures in hand. He's the man that can best tell you your options for his products. Burnham doesn't like to see customers having problems like yours.

Pete

 

I think ultimately you would be throwing money at a problem that is not worth throwing money at. However, you asked, so....

[Caveat: I'm not a hydronic systems engineer. I'm a slightly-educated "hydronic hobbyist." The following, as usual, are thoughts and opinions and potentially quite incorrect.]

If you downsized to an RV-4 (I have one, with two fin-tube zones and a 40-gal indirect, run by a tekmar ODR control), I would guess the fuel savings would be somewhere between imperceptible and 4-5%. If you downsized to an RV-3, then maybe 4-8% (again, these are WAGs). With that two-stage ODR control, your RV-5 is running as good as it gets. That's a very, very efficient system for a cast iron boiler.

I think if you went with a smaller RV (or at least the RV-3), your indirect recovery would begin to suffer. You probably wouldn't notice the difference in indirect recovery if you went to an RV-4, but see above for potential savings. Negligible, I'm guessing.

Adding another indirect? That would certainly complicate things where controls are concerned. Going larger? Do you need to? You mentioned a whirlpool. Once you get into high-gpm, large DHW loads like that, you are generally obligated to go with a boiler sized to the DHW load, which you have. There are a few ways to "cheat" that a little, such as running the tank at ~140F and using an anti-scald tempering valve to supply ~115F to the fixtures. But again, downsizing will likely result in very minimal savings.

The nice thing about mod/con boilers is that they can deal with low space heating loads (by modulating down), and high DHW loads (by modulating up). But in your case with such a substantial investment already made in a very efficient system, I just don't think it's worth it to toss a not-cheap boiler with a very good set of $controls. Might take you a decade (or more) to make back what you spent doing the changeover.

In your shoes, I would
a) control the RV-5 with a 2-stage control (you already have this. Great.)

b) get that reset curve down as far as you can, so that you are supplying the coolest water possible to satisfy the heat loss.

c) spend your money on something else. For $5k, you could make significant headway on a solar DHW system, and potentially even integrate it with the space heating. Your existing boiler and contols are basically ready to do this. Payback on solar DHW in some cases is as low as 3-5 years. Get a ~120gal dual-coil indirect tank (one coil for the solar, one coil for the boiler as a backup when it's cloudy for a week). You'd likely never run out of hot water again.

Or save your money for...

d) 6-10 years down the road when there are more and better options for hydronic heating (fuel cells, robust multi-fuel boilers, solar-integrated, whatever), at which point you might consider ditching the current setup altogether.

 

thanks again for those thought provoking replies.

Glenn stanton knows my situation well. I was a little ticked off at Burnham last year because NO ONE would talk to me from Burnham's tech dept. I posted on the wall and Glenn hooked me up with Ron Beck. Ron made the Taco 2 stage recommendation. So Burnham came through in the end after a little bumpy ride.

I have tweaked the taco to no end. I have my settings set to what I believe is as efficient as she's going to get. Its just that my home is very energy efficient except for this oversizing. But after talking with this forum and the wall I'm not doing too badly.

At this point I have to agree that the savings will not justify the cost. Best thing is to get 10 more years out of the Revolution and see whats available (hope i'm available) at that time. Who knows I might be living in Florida...hehe

Thanks much for your time. I appreciate all your help...Regards

 

I do?

Me first!!! But if did, I think I'd actually miss my Prestige.