Did my HVAC guy dramaticlly oversize my boiler


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Old 03-13-13, 09:27 PM
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Did my HVAC guy dramaticlly oversize my boiler

Just from reading these threads ,I'm REALLY thinking I'm way oversized.
OK heres what I have going on,,,I have a WMG oil fired boiler. We finally got gas on our street last year so I'm getting rid of the oil(thankgod almightyI'mfree atlast)(well almost)
so the oil is 115000btu
But the new WM ULTRA is a 155
It also handels the DHW
Now heres the thing ,my house is only 2000sf rancher,hotwater baseboard,2 full baths
3 zones including the Hot water.
From what i'm reading ,these guys that have the 155 are heating 3-4000 sf houses and apartments.
I asked him about it and he said its better to go bigger and its only a couple hundred$$ more
But from what I'v been reading,,,IT'S NOT better
Am I reading things wrong or am I way oversized
Thanks for any input
 
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Old 03-13-13, 09:49 PM
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To be certain you need to "run the numbers' by doing a Manual J heat loss calculation. But yes, you ARE seriously oversized.
 
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Old 03-13-13, 09:52 PM
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Welcome to the forums.

Bigger is not better.......it just costs more to run.

Have you done or was a heat loss calculation done ?
I know how to do the calculations but I'm not sure how the DHW figures in the equation.

A couple of sites for loss calculations. Basic formulas.
calculate heat loss
Rough Room Heat Loss Calculation

The pro's will stop by and give their opinion.
 
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Old 03-14-13, 03:27 AM
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The Heat loss is around 60000
 
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Old 03-14-13, 04:49 AM
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2000sf house
about 35 years old
from what Im seeing I needed @90000 btu
but thats not includeing the DHW (Amtrole 55 or 65gallon) 2full baths.
the 155 has an output of around 124000
 
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Old 03-14-13, 07:31 AM
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FYI - I heat a 2000 sq ft cape style, 45 years old, 3 bed, 2 bath 2 zone baseboard with a DHW tankless coil easily on 80,000 BTU oil fired 20 year old "oversized" boiler. I'm firing it at its lowest recommended firing rate and I have to use the Intellicon HW+ to help avoid short cycles.

I'm oversized, but managing it. You will be way oversized.
 
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Old 03-14-13, 09:42 AM
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90,000 BTUs for 2,000 square feet seems pretty high to me. I suspect that 60,000 would be more in line.

Generally the input to the indirect heater is ignored when sizing the boiler to space heating. As long as you have a priority control with time-out feature there is almost never any need to consider the water heater in sizing the boiler. Worst case is that the water heater recovery will take a few minutes longer.
 
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Old 03-14-13, 02:32 PM
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Well I'm stuck with it now
Iv got a few choices
Just use it
put radiant floor heating on my back porch ,driveway and sidewalks
I could heat the Neighbors houses
Or I can try to sell it to a customer(which means I would have to sit on it and buy another one.
Im so mad at this guy.I havent even called him to tell him about my findings.
Hes a heating guy so maybe he can sell it(doupt it but??)
aarrrrrrr
 
  #9  
Old 03-14-13, 04:08 PM
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I would make your heating guy take it back and supply the correct size unit. If you install it, it's going to be very inefficient. Show him an actual heat loss calculation so you have the numbers to prove his selection was wrong.
 
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Old 03-14-13, 06:41 PM
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Is there a rough rule of thumb for oversize inefficiency ?

Like, a 100% oversized unit will be 30% more costly to run during the peak heating
time (and worse than that during the shoulder seasons) ??

Just curious..
 
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Old 03-14-13, 06:51 PM
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I have heard numbers up to 40% depending how much oversized you are. The problem with over sizing a mod con boiler is the fact that you lose the lower end of modulation. This is where you spend most of your heating season at the lower firing rates.
I would get the proper sized boiler.
More on heat loss.
Heat Loss calculation
Heatloss FAQ
 
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Old 03-14-13, 09:01 PM
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Tom
That would be a good way to go but he had me go to the supply house and buy it useing his name to get a discount.I called them and they said since I took it out of the creat they wouldent take it back(even though I could put it back in the crate)
Will call my Credit card company to see if theres anything they can do.God no's what thier restocking fee wwould be??

I just did both of these ,calculate heat loss came out to 55934
Rough Room Heat Loss Calculation total Came out to 84096
Does that mean I need a 85000btu unit
 
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Old 03-15-13, 05:59 AM
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No you don't need 85,000 btu's. it just shows how many flaws the short cut heat losses have. Been saying that for years. Even on manual J novices normally miss things or do not enter info properly.
I actually did my home probably 10 times if I did it once. The manual J had me just under 40k. The worst one had me at 91K for a home of 2800 sq ft. I am heating with about 38k.
I would go with the smaller heat loss. That sounds more reasonable for 2000 sq ft. Unless you have a loose home.
 
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Old 03-15-13, 06:06 AM
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I'd call the CC company and see if they can help you. If by chance you put it on Amex, they will totally go to bat for you. Your heat loss seems high on the one site. Other experts might have more info for you.

When I purchased my home, the boiler was fired at a rate that was producing 110,000 btu's and I went through 900 gallons of oil. I have since down fired it according to the manufactures instructions and also put an Intellicon heat manager on the system. I went from 900 gallons a year to just around 600 gallons a year. A dramatic savings to say the least.

Size does matter and I've got the numbers that proves it!
 
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Old 03-15-13, 06:51 AM
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FYI, the ultra is a modulating boiler if it is installed with an outdoor sensor. The total capacity is a lot more than what you need, but you may not notice a huge spike in gas usage because it is modulating. It sounds like your contractor is someone who is not concerned with energy efficiency but rather with covering his butt in the case of undersizing and not being able to maintain space temp. If you truly do need 90k btu then it may be the correct ultra boiler for the application. The next smaller boiler is 105k input with an output of 94k btu which would be marginal but most likely the correct size needed.
 
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Old 03-15-13, 07:24 AM
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Even though the boiler modulates it's input it will come on and fire to max on a larger delta-T. It will search for a good place to fire but keep searching. The problem is if you need 50 - 60k to heat the home the boiler only turns down to 31k. Split that into two zones and each zone requires 25k to 30k. The bigger problem is flow your house requires about 6 gpm flow. The boiler is probably somewhere in the 10 - 15 gpm range. Hot water will flow up the supply and what does not go to the supply will go between the tees and return right back to the boiler pre-heating the return in the process thus causing short cycling. The boiler only fired at minimum may be close to 100% oversized. Can the fan speeds be adjusted to reduce input? That would help if it can be.
 
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Old 03-15-13, 04:31 PM
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I dont think the ccard company would be willing to work on that one.. it was the unit requested at the desk and even 'recommended' by the 'pro'.

How about an external tank to dump/store some btu's on each run to minimize the short cycles ? Do you have room for 40 or 60 gallon well insulated tank ?
 
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Old 03-15-13, 08:00 PM
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First off someone is coming over tomorrow to do the heat loss
Hes NOT selling me something,hes just doing the heat loss and telling me what size I should get
I read the receipt that I got with the boiler and it clearly says If you have the boxing it came in you have 30 days to return
I also called AMX and they said I could return it even if I didn't have the Box.
I'm not going that route yet,but I will if I have to.
One way or another its going back.

From hours and hours of reading and comparing other peoples units and house size I'm figuring it's going to be between the ultra 80 and 105
Another thing I remembered was when I moved in here it had 80000 BTU oil ,when we put in the new oil they(fricking salepeople) raised it to the 115000.Then if I dident come on here it would have gone up to 155000.Then in 15 years it would have been 200000 Its a VICIOUS cycle and it stops here
 
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Old 03-16-13, 01:50 PM
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ok ,heat loss came in at 53750 but add some corections(?) so its at 55000
He's telling me to go with the ultra 80
does this sound better?

And someone else said the CSA minimum input is 31(on the 155) so the 155 would be fine .He said it can run as low as 31 if nessasary. From what I'm reading The 155 low rateing is 123MBH
I think hes reading something wrong ,but I no to little about this to tell him what it is
 
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Old 03-17-13, 06:52 AM
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I have so many opinions comeing from everywhere its getting frusterateing ,
The 1 HVAC guy that had me get the 155 in the first place
says the Amtrole boilermate will account for 50K BTUs
so the Ultra 105 output of 94k BTUs would be maxing out the boiler

Everything Im reading on the internet says 60k- 80k is all I need
Thats dropping from a 100K oil fired ,that makes me nervous
I dont want to order the wrong size again.

And does the CSA minimum input have anything to do with it?
 
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Old 03-17-13, 07:33 AM
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You wont be space heating and dhw heating at the same time..........
 
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Old 03-18-13, 02:30 PM
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Got it.Thanks
I no how to read,it's just understanding it that I'm slow at
If you or anyone can tell me I'm on the right track or not.........

My heat loss results are =
UA(BTUhr-F)=851
DesignLoss=55293
year loss=102.1
Fuel cost=$1276(10year=$20327)

What I'm finding out is ,
I want to size up my heatloss to match the NET IBR RATEING,Right?
If thats the case the 80 would be my boiler of choice,Right?
The NET IBR of the WEIL MCLAIN ULTRA 80 is 62, AGA Input= 80, DOE=71
Whereas the 105 ultra is Net IBR123, AGA=105,DOE=94
The 80 would actually be alittle big but it will give me some room for a 3-400sf add-on

AM I in the ballpark here with my thoughts, or am I way out in the back of the parking lot (by the porta potty)?
 
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Old 03-18-13, 04:47 PM
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Sounds better, if you check my earlier post I stated around 50k to 60k. You o not size on the "net output" you size on the "DOE" or "Gross Output".
The operational btu requirement is normally going to be about 15-20k btu's due to warmer weather. Now break that down to a single zone running and you will be about 10-12k. Does a minimum of 31k sound too big?
You still have enough for the addition and DHW with the 80k boiler.
 
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Old 03-18-13, 06:36 PM
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Thanks rbeck

Thanks to these forums I'm finally on the right track.
and not so nervous about putting in a smaller unit
Alot of info is getting stuck between these ears
I'm in the construction field and n have dealt with 15 different HVAC guys over the past 20 years.
NOT 1 of them has ever done a Heatloss.
Thats gotta change
 
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Old 03-19-13, 08:31 PM
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With no fears of regrets I have ordered the 80k .
Thank to the Internet and the help forums I have averted paying for my boiler for the rest of my life.
I believe it will pay for itself in 2 years maybe 2.5 with the hit I'm gonna take with the return and restocking fee of the 155
Now on to search on the proper way to install it because after all this ,I'm REALLY not trusting the HVAC guys to do it right.
Thanks everyone for your help and patience
 
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Old 03-31-13, 06:39 AM
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Charlie,

I was in the same poition as you last Spring. I have a old, 1860, Sea Captains house on Cape Cod of 2300sq/ft. It was updated with widows and insulation when we renovated it 20+ year go. At that time we had a new gas boiler of 145Kbtu installed. It was baed on a heatloss done by a third party tat was WAY off. I was totally ignorant to hydronic heat at the time an just went with what they said. The boiler was a W/M VHE3. All it did was short cycle even in the coldest weather. We went through ignitors every year or so. That should have been a clue but the new plumber I hired to replace the WM after 23 years didn't catch on and replaced it with another WAY oversized boiler, an Alpine 150. Long story, but it would not keep the house warm on an unusal cold spell we had this winter. The reason being was short cycing kept the average water temp lower than needed. Called him back and he did not have a clue except to say, now get this, "well the old boiler probably was heating the water to 200* and these newer Mod/Coms only heat to 180*. He actally wanted to add more raidiation. About that tme I retired from my airline career and had time to look into the problem. When realized what was going on and how he did not have a clue as to how to properly size and install a new Mod/Con boiler I called him back again. Told him I had done both a heatloss calc and a fuel used calc to determind the heatlos of the house. I came in at 60-62k Btu. With that in hand I insisted her remove the 150 and replace it with an Alpine 80. He agreed and hopefully it will be done by next week.


The point of my rant is that a heatloss calc is mandatory and most installations seem to be oversized by a factor of 2 or more. To get the most out of an expensive mod/con boiler, lower than 130* return water temps are needed. When you oversize a boiler the problem is not the high limit its the low limit that will be ruining your efficiency. You need to modulate down low enough to be able to get the lower return water temps without short cycling, which also adds to a shorter lifespan for the boiler.


Tom
 
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Old 03-31-13, 09:56 AM
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Wow ,You have to give your plumber credit for coming back to replace it(even if he did oversize it)
Keep us posted on that.
As of now I'm looking to be up and running Mon or Tues,,,cant wait. oil tank probably has 15 gallons left in it,temps at night are cold enough to use the new boiler for another month or 2 befor summer sets in
On top of the new boiler I insulated the pipes and had the guys redo the 1 zone that was a figure 8 and added a baseboard to the back room that didn't have heat.
I'm still a little over sized but within reason, and I just thought about your comment on needing below 130 return temps... I can take the pipe insulation back off to get it down a little if needed
The guys that are doing it are doing a very clean setup
The reason I chose them to install it is because they are the only ones to say I didn't need anything bigger then an 80k
With that said I don't believe they n have ever installed a WM modcon before so I'm reading up on the setup (as I'm sure they are also)Keeping my fingures crossed
As I said,,,I cant wait
 
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Old 03-31-13, 04:59 PM
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Charlie,


I was also very impressed by the professional looking installation of my boiler. Plumber did neat work just not up to speed on mod/con boilers. In my experience here and talking with others, most arn't.


You should ask you installers if they have set the Delta/T's and the outside reset for correct operation. If they look at you like a deer in the headlights your in for a fun learning process. The Delta/T's need to be correct on both the primary and secondary circuits, if its plumbed that way. Its a matter of getting the flow/GPM correct.

Mine is not even close. They will change with the new boiler as the boiler circulator is a different type with the new boiler. Will be addressing that when I get home Wed.

Will post again.


Tom
 

Last edited by tom3holer; 03-31-13 at 05:18 PM.
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Old 04-03-13, 08:59 PM
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I was also very impressed by the professional looking installation of my boiler. Plumber did neat work just not up to speed on mod/con boilers. In my experience here and talking with others, most arn't.
well heres another installer thats not up to speed with mod-cons
Yesterday they told me
they would shut me down today with the garrentee that I'll be up and running by the time I got off work.
Im looking around and see all this other stuff that should get done ,,,but he says yes
well here I sit with no hot water or heat
I told him ,"I want it done by the book"
Its like he dident even read the book(I did)
I have a Tasco 3 zone relay from the old boiler that he was going to use and I had to demand that he use the 3 spots in the ULTRAs u controle
As far as I no they are there for a reason
1 for the boiler 1 for the DHW and 1 for what ever
I'm pretty sure I have to track down a Weil mclain guy to go over everything to make sure its right. we'll see tomorrow
If everythig is good I pay the weil mclain guy and the installer
If the WM guy has to fix stuff , it comes out of the installers pocket
 
 

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