Radiator sizing

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Old 08-26-13, 05:27 PM
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Radiator sizing

Ok the first of 4 contractors came today to give me a proposal to replace my electric boiler with a nat Gas unit. He measured the cast Iron radiators in each room but that was all he did as far as calculations go. I have included my measurements below.
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So what info can he or I get from these measurements besides the max capable output of the radiators? How could I calculate this as well?

He quoted 110-120K BTU unit off the top of his head, then I asked about the existing 68K BTU unit. He said that they size the unit then add 15-20%.
I'm not sure how he is going to size boiler just by using the radiator size?

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He is also saying HE condensing unit is the way to go.
I thought that the cost to payback on condensing boilers was to high to make it worthwhile?

He specs Bryant and Weil McLein

Discuss.....
 

Last edited by Frank_S.; 08-26-13 at 07:16 PM.
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Old 08-26-13, 05:35 PM
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I don't think he is on the right track. Your concerns are well placed.

Have you run a heat loss calculation yet? That should come first. Prospective contractors probably won't ever do it - so it's up to you to do. Otherwise, you will be at the mercy of a boiler salesman. You run the numbers, and then you tell the contractor what size boiler you want.
 
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Old 08-26-13, 06:29 PM
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He quoted 110-120K BTU unit off the top of his head, then I asked about the existing 68K BTU unit. He said that they size the unit then add 15-20%.
Nope... run away.

He can't even do the math! Add 20% to 68K and come up with 120K ? Really ?

Or, is he saying that he sizes the unit to the installed radiation and then adds the % on top of that?

Either way, WRONG ANSWER!

I'm not sure how he is going to size boiler just by using the radiator size?
Short answer, he can't.

It is a somewhat all too common fallacy... even fantasy... that the boiler should be sized to match the installed radiation. It is NOT so.
 
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Old 08-26-13, 07:23 PM
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i ran the slant fin calculator and came up with 50382 Now how accurate that is remains to be seen But I can give anyone willing the info to run a comparable calculation.

This guy was the owner of the company who said he'd been doing this for 43 years. Old skool guy doing things the old skool way I guess. i have another contractor coming on eveyday this week except wednesday. Anyone here want to come by and do it right? I just hope I can find someone competent at a decent price point.
I hate spending money on something i should be able to do.
 
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Old 08-26-13, 09:45 PM
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Someone claiming to have 43 years of experience when the truth is he has one year of experience (or less) 43 times over. Unfortunate, but all too common in the heating trades.

Do your own heat loss (as you have) and don't let ANYONE try to sell you on a larger boiler. The heat loss calculation is based on the coldest outside temperatures to be expected and these calculations have a built-in fudge factor. Size the boiler closest to the calculated heat loss and you will be fine.
 
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Old 08-27-13, 03:06 AM
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New calculation with Crown boilers calculator:

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The number I got from Slant fin calculator was 50382 the second time I ran it and around 60 K the first time so it looks like I'm on the right track. From 45-65K BTU should be fine. No where near the 100K mark. I also did a radiator calculation and it looks like the radiators will output 90600 BTU
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Now as to "regular " boiler or Mod/con boiler... Since I am replacing an electric unit which will be more cost effective long term?
 
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Old 08-27-13, 02:44 PM
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2nd contractor went directly to the basement looked at the electric unit . We discussed new valving and cutoffs, Some more about whether i was interested in an 80 something AFUE or the 90 something type. He uses New yorker and Weil McLain. His thought was simple is better in the long run. More to go wrong with the HE units.
He measured nothing and looked no further than the basement. Talked like he was pretty knowledgeable but I'm overall disappointed. I had high hopes for him.
So far Angie's list is disappointing me.
 
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Old 08-27-13, 03:03 PM
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Since you have more radiation than you need, that's a plus for a mod/con because it means that you can heat the home with cooler water.

Note that the 'conversion factor' for hot water is at 190. I've seen various ratings for cast iron rads ranging from 150 to 185 BTU / SQ FT. Chances are that you will NEVER need to run 190 water to heat your home. My guess is coldest day you should easily heat the place with 150 or so water.

Now as to "regular " boiler or Mod/con boiler... Since I am replacing an electric unit which will be more cost effective long term?
There's been lots of discussion over the years here on the forum on this subject.

The discussion really should have nothing at all to do with what you are replacing. It really has no bearing on the choice of a new boiler.

In my opinion, the down-side to a mod/con is the continuous maintenance costs. With a conventional gas fired boiler, there is very little (near none) yearly maintenance. Mod/cons should really have a yearly checkup and cleaning and this could cost maybe $150. In order for this service to be performed properly, you will have to find a tech that KNOWS WHAT HE IS DOING... and it sounds as if you may have trouble in that department.

In the case of a mod/con, it is probably NOT a good idea to look for the 'old timer' with 43 years of experience. You need a 'young buck' with factory training under his belt and good work ethics.

I don't have the numbers and such to do a projected cost of ownership analysis between a mod/con and a conventional boiler, but my guess is that the conventional would win.
 
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Old 08-27-13, 04:41 PM
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My home's calculated design heat loss is 105,000 Btu/hr - twice yours. With my decrepit (but reliable) 60-year-old boiler, my annual gas bill for space heating runs around $1,000. Let just assume that your bill, with a modern conventional boiler, should be $500 per year.

If a mod-con would save 15% fuel, that equates to $75 per year savings. But, now subtract the $150 approximate annual maintenance required for mod-cons, as mentioned by Trooper. You're left in the hole by negative $75 - and you have already paid the extra initial cost of a mod-con, which there is no return on.
 
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Old 08-27-13, 06:58 PM
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You've invited four different contractors, and have met with two - and their suggestions are questionable. If you call in 44 contractors, you may not know much more. Few will, if ever, bother to really check out your situation and propose the most cost-effective solution. Boiler salesman, operating on a commission with limited skill, might be compared to used car salesmen, except that is unfair to used car salesmen.

You've got two options: pick the boiler salesman that talks the best line, or run the numbers yourself, and tell the salesman to quote you his price for what you want and need.
 
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Old 08-29-13, 07:28 PM
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Hurrah!!
Contractor 3 actually measured all the windows doors and acted like he had it together. Now we'll wait and see what he comes up with for load calculation and boiler recommendation.
 
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Old 09-04-13, 05:30 AM
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Ok contractor 3 got back to me with his quote. Wow. He even did the heat loss and gave me the number - 29718 then specd a Lennox GWB8-075E-2 which is at least double.Name:  woods.jpg
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I have asked for a further breakdown in cost. The cost of his boiler is nearly as much as contractor is complete install.
I guess I may have to follow Gil's advice and just pick a boiler myself and then farm out the install.
Anyone want to come to Virginia for a few days?
 
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