Boiler replacement help

markp1 · September 2014

Hi,
I'm looking to replace my 40 something year old natural gas boiler with something a bit more efficient. House is heated with fin-tube baseboard. After watching all the video's on the Taco site, doing a degree day heat consumption analysis based on my actual usage, doing a room-by-room manual J load calculation, and measuring my baseboard / mapping the zones, here it is:

2500 sq ft, 2 story home, 2x4 walls with fiberglass bats, in Topsfield MA (5F design day temp)

Degree Day analysis = 45k BTUH
Room-by-Room Manual J = 58.5k BTUH

Zone 1: 13.5k BTUH, 41 linear feet of baseboard, 120 ft of pipe ~ 7.2 ft head
Zone 2: 15k BTUH, 42.5 linear feet of baseboard, 100 ft of pipe ~ 6 ft head
Zone 3: 8k BTUH, 53 linear feet of baseboard, 140 ft of pipe ~ 8.4 ft head
Zone 4: 22k BTUH, 102 linear feet of baseboard (1" start splits into 2 parallel 3/4" loops), 150 ft of pipe ~ 9 ft head

Zones 1 and 2 are both the main portion of the first floor, and their thermostats are always programmed the same... I could combine the two into a single zone, giving me:

Zone 1-2: 28.5k BTUH, 83.5 linear feet of baseboard, 150 ft of pipe ~ 9 ft head
Zone 3: 8k BTUH, 53 linear feet of baseboard, 140 ft of pipe ~ 8.4 ft head
Zone 4: 22k BTUH, 102 linear feet of baseboard, 150 ft of pipe ~ 9 ft head

Does my above degree day analysis / manual J room-by-room look ok?

Assuming I go with the higher number (58.5K BTUH), I'm trying to determine what boiler to go with (I plan on adding an indirect water heater to the boiler in addition to the above zones), and whether or not combing zones 1 and 2 would help.

Any advice is greatly appreciated.

Thanks,
Mark

j a_2 · September 2014

Thinking your part of the early boiler replacement program…If you do go high efficiency,be sure to get a full explanation from your installer how they intend to set up the boiler to operate as efficient as possible with copper fin baseboard…Ask them at what boiler temp. does is stop condensing…If they can’t answer that,send them packing…..Make sure they are trained by the manuf. who’s boiler they propose to install,and can they service it should it break down,,,Heat loss is basic math with a little common sense…Generally speaking boilers jump up pretty good in size from model to model…If your sizing a boiler a whole house heat loss is a pretty good indicator of total B T U…Your very smart to be asking the questions now and not after the fact….Good luck

unclejohn · September 2014

If you are going with a indirect, and you should get a Triangle Tube 110. Last I saw though was aprox 500 BTU's per foot @ 180*, so 102' = give or take 50K BTU's

Rich_49 · September 2014

Mark
You have several zones , a couple which at lower outdoor temps will require some buffering . Take a look at this boiler and add the indirect whenever . You are falling into the same trap where many get hung up , having enough BTUs when you should be more concerned with the lower end . Making it big enough for all your future needs is a consideration , but not all that difficult . Take the time to look at this and remember it cannot be oversized . 4 sizes , 100 , 130 , 160 , 199
http://www.htproducts.com/pioneer.html
Remember that this gives you the mass to not shortcycle based on programming the Differential properly , has outdoor reset and you can kook up your indirect later . Just size the maximum you could expect to use for either space heating or DHW . Use the smallest Indirect you can while storing at 150 - 160 * using a mixing valve (ASSE 1017) . You can make a 40 perform like a 75 gallon and a 30 like a 50 gallon . Be smart .

markp1 · September 2014

Thanks everyone for the advice. My hot water requirements are relatively high... jacuzzi bathtub in the kids bathroom, and a double shower in the master bathroom, etc. If both showers in the master are running, that's 5GPM, which if the indirect was full and 53 gallons (the Viessmann indirect for example) I'd get just over 10 minutes of shower time. I'm planning on the 53 being the smallest indirect I'd put in, but more likely a 60 or 80 gallon.

Right now I am leaning toward a Viessmann 200 B2HA-19. It has a min fire of 10.9k BTUH, and a max of of 61K BTUH. Thoughts on the Viessmann?

icesailor · September 2014

You're really not understanding your question. There's far more usable hot water in a 50 gallon storage tank than you need for a shower with two, 2.5 GPM shower heads (5 GPM). Because if you set the tank control to 120 degrees, you have to add cold water to the hot to make it safe to use. Which is around 106 degrees. (If you think you can stand a 120 degree shower, you can't). So, if you store the water in the tank at 140 degrees, you have to add more cold to the hot to get the same 106 degree water out of the shower head. I'm sure that there is a formula to figure it out. It doesn't work because of human differences.

If you go to fill a large tub (like a Jetted tub), never turn on the hot water wide open and fill it most of the way, then top it off with cold. The hot will run out. If on the other hand, you mix the water to a comfortable level and fill it with mixed water, you will fill the whole tub and have hot water left over. At least, that's how it works in real world experienced practice.

Increasing the water temperature in a particular sized water heater storage tank, increases the theoretical size. Due to the more usable hot water to mix with the cold in practical, real world application.

markp1 · September 2014

Icesailer, I think I understand where you are going... this is where a thermostatic mixing valve between the cold line going into an indirect water heater and the hot line coming out of the indirect water heater comes into play, right?

So I can keep the water in the indirect at say 150, but have it mixed down to 106. If it was a 50 gallon water heater with 150 degree water in it, I'd be able to fill a bathtub much larger than 50 gallons with water at 106 degrees.

heathead · October 2014

Mark,

Check Ebay today they have a dented indirect viessmann 80 gal. tank that ends in 5 hours. thought you might want to know. Their are two in the picture but you can't choose between them one looks better than the other.

Boiler replacement help

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