Need help with loop and pipe sizing

mattbbb14

Hello, first post here. Hoping to gather some needed information as a homeowner about some changes I'd like to make with our boiler system. Currently we have a 1100sqft 2 story house with a 75kbtu crown boiler on a single 3/4in loop with 66ft of baseboard fin . The house is from the 40s and has very little insulation and an uninsulated dirt floor crawl space. Our system was installed in 2014 (no idea who did it as we bought the house in 2016). I believe our loop is too long. The second floor is always cold and I believe the largest reason is because the upstairs is at the very end of the loop. I also believe the second floor is short on baseboard units too. 

My first thought is to separate the first and second floor to create 2 shorter loops which should help with hot water getting to the second floor. The system has a single B&G circ (on the return side). The supply side starts at 1in and is reduced to 3/4 after the expansion tank and air separator and the 3/4 continues throughout the house and the circ before transitioning  back to a 1ft section of cast iron (1.25in I believe) before heading back into the boiler.

My intention is to tee off the 1in line after the expansion tank with 2, 3/4in loops for the separate floors. When both 3/4in lines return, I assume they both need to be teed into another 1in line before going into the circ and returning to the boiler? I planned on adding shut offs on each side of the 2 new loops for isolation purposes. 

Am I on the right track with my logic? Am I missing anything important? Are check valves nesessary in any spot? I'm new to all of this but very handy. Any help would be appreciated.

hot_rod

Yes you are on to something. You drop temperature as you travel around the 66' of fin tube. Ideally a room by room heat load would indicate how much heat is needed in each room. Then determine the temperature drop to determine how many feet are required. I use HDS to model the load of each room, select a fin tube model, and it shows the design.

Splitting the loop will in fact provide higher SWT and might get you over the hump in the under heated areas.

IF you want confirmation, download the ap at www.slantfin.com and perform a room by room load calc, see how the amount of fin tube matches up.

mattbbb14

I downloaded the app to figure out the load for the individual rooms. Very helpful. As I imagined this helped me figure out I need to add some baseboard units in a couple of the rooms as I suspected. However the second floor is almost on par with what's recommend so I'm definitely thinking separating the loop will make things more comfortable. I will also pick up a laser thermometer to measure the temp differential between supply and return. Any thoughts on the plumbing layout I mentioned? With regard to pipe sizing, tees and if check valves are needed?

EBEBRATT-Ed

Just put a balancing valve on each loop in the return before they are teed together. Make the supply off the boiler to the tees 1" so a 1 x 3/4 x 3/4 tee and make the return to the boiler the same way if you can.

What the original installer should have done was figured out the water temperature drop and used a little extra radiation in the rooms toward the end of the loop.

Splitting the loops is a good idea. 66' of baseboard on a 3/4" loop is max

mattbbb14

Thank you. I completely agree it's too long of a loop. Especially considering that the pipe for the entire first floor runs through an uninsulated crawl space,and the pipes don't have insulation either.

mattbbb14

I measured the supply and return temperatures. Supply is 178 and return is 148. Looking at about 30 degree differential. Is that about normal for a 3/4in loop? Considering the second floor is at the end of the loop it definitely makes sense why we're having more issues up there.

hot_rod

Most times a designer will use a 20 delta for a fin tube job.

One way to look at your system, 178+148= 326 ÷2 = 162° average water temperature. Then look at the fin tube output sheet at 160° to see hw many BTU you are transferring.

Two ways to increase output would be to raise SWT, and AWT, or increase flow rate. Increasing flow rate brings down that delta, so AWT increases and does output.

You want to keep flow velocity under 4 fps feet per second, to avoid noice, so only so much you can squeak out by increasing flow rate.

By splitting the loop you will increase the AWT and the output.
Plus you could have two individual zones if you want.