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[jackh113]

Pulled the trigger on a P&M BL 2840, now I'm figuring out the materials for the rest of the install.  I've followed the Taco Pump Sizing Guide from other threads and it doesn't seem to be adding up right.  Can someone check my math here and give some input?

First my setup.....OWB will be about 90 feet from the house so call it 100 with turn up into the stove and house (no basement so have to turn up through the wall).  I will have approximately 25' of pex one way to the DWH plate exchanger and heat exchanger coil in the plenum.  My house is about 3200 sqft and according to a manual J done by my HVAC guy has about a 90,000 btu load.

Given all of this I have calculated my target flow rate to be 9 gpm with a 20 deg Dt.  With that flow rate, it looks like I need to be running an 1.25" pex.  Estimating my total circuit to be 275' multiplied by a factor of 1.5 to estimate additional pressure loss due to fittings, valves, etc. (as given in this article from another thread http://www.fueloilnews.com/ME2/dirmod.asp?nm=&type=MultiPublishing&mod=PublishingTitles&mid=8F3A7027421841978F18BE895F87F791&tier=4&id=663F2C7F5BA543968C4AAB1732E86FFB ), I come up with a head loss of 14'.  I come up to a Taco 0014.

This seems large to me given that I've seen a lot of guys on here running 1" pex and 008 & 009's.  I know every application is different but just want to get some input from some of you more knowledgeable guys.

I had originally planned on running 1" pex until now.  What would the downside be to this?

Also I'm thinking about going with a variable speed delta t pump.  How would this affect the pump size calculated above?

Thank for any input given guys!

[Sprinter]

You need to calculate total equivalent length of pipe for your main run, multiply by the pipe brand specification head loss value given at 9 GPM@ designed supply temp. This equals your head. Now look at the curve chart and plot your dot when your head loss and GPM meet. Now look at which curve covers best.

Yes its time consuming figuring each fitting or adding each HX specified head loss, but this takes the doubt away. You can even calculate the cost of electricity used to see if small pipe+large circ price+electricity usage cost is more than large pipe+smaller cheaper circulator+lower electricity usage cost is better for you.

9 GPM can easily be handled by a $70-$130 circ. And a variable ECM circ will use 1/8th-1/20th the electricity of a high head circ.  it's the cost of the larger supply pipe that makes or breaks the sale. And exactly why so many get stuck with the cheapest option..

Another thing to figure is, will your house demand be 90kbtu every time it calls for heat. Or can it be broken down to smaller zones? 90kbtu seems on the high side unless it poorly insulated or low design temp.

Nice link too by the way....your on the right track.....

[Sprinter]

Well the pex ID or its K value is the important variable.

TELp x C x K x Fd = HL.

275 x .964 x .000794 x 46.765 = 9.84hL

Total equiv.length
Fluid temp correction flow factor 170 degree average S&R the higher the better.
K is friction value of fluid flow in pipe
Fluid flow in GPM factored to 1.75 corrective.

Key numbers are the TEL and GPM

[jackh113]

Thanks for the input sprinter.  I haven't laid out the system or chosen heat exchangers yet.  Guess that should probably be my next step and back into this thing a little more.  Don't mind the calculations or schematics part.  This just seemed like the place to start but I can see now I'm going at this bassakwards.  lol

The heat load is a little high, but yes the house is older and poorly insulated.  Planning to replace the ductwork, add 10" of insulation to the attic, and do some air sealing while doing this.  My wife bought the house 6 years ago before we married and it had just been remodeled.  I'm telling you the guys who did it should be shot.  You should see my electrical!  lol  I'm a Project Manager for a custom home builder and been in construction all my life.  Done a few remodels myself.  It would give you nightmares some of the stuff I've found that they did.  lol  Slowly fixing what can be fixed......

[jackh113]

Well the pex ID or its K value is the important variable.

TELp x C x K x Fd = HL.

275 x .964 x .000794 x 46.765 = 9.84hL

Total equiv.length
Fluid temp correction flow factor 170 degree average S&R the higher the better.
K is friction value of fluid flow in pipe
Fluid flow in GPM factored to 1.75 corrective.

Key numbers are the TEL and GPM

This is the formula I used from the Taco Sizing Guide.  Guess I screwed that one up.  Have to go back and see where I went wrong.  Thanks again.

**edit:  Just realized this is the pex only.  No fittings or exchangers.

[Sprinter]

Right, but there are several ways to do the HX, open tank/coil. Flat plate.
It sounds like your atleast figuring this stuff out on your own and then asking questions.

Its good to have an understanding even if you don't install it yourself.

I just don't know where taco got their K value #'s , it doesn't say whether that's .825,.876,.905 or 1" ID. And even different  brands with same ID can have different K. Oxy barrier versus non. I know that's a small number but it adds up on long runs.

Bumblebee VDT circ, running 24/7 @ 9-42watts 5.8-16.3gpm $2-$7/yr. circ price $177
007 Taco $31-$34yr ;  $2.74/month 2-15gpm. Price $75.   Same as 15-58
009 Taco $133/yr. ; $11.05/month. 1-10gpm.  Circ price$215
0010 Taco. $$98/yr.  2-33gpm.     Price $216
0011 Taco $224/yr 2-31gpm.        Price $242
0012 Taco $131/yr 2-53gpm.         Circ price $360
0013 Taco $254/yr 2-33gpm.        Price $278-$320
NRF36 $291/yr.  2-36gpm.           Price $306
grundfos 26-99  $266/yr 2-34gpm. Price$ 260

Add in underground mainline of choice
1" price versus 1.25" versus 1.5" price difference then minus the difference in yearly or heating season cost to run circulator. This can turn into a pretty good cost analysis thread.