Do I have a converted gravity system, or is the Taco Flo-Pro software wonky?

R2.0

As part of my boiler replacement I used the Taco Flo-Pro software to calculate the heat loads in my house. I figured that, since I was in it anyway, I would model the system as-is, and that would give me a baseline for future changes. Ugh. To say that the interface is "quirky" is generous. But it's done now.

The house is hot water 2 pipe direct return. All the piping, except the near boiler, is 1 1/4" headers and 1/2" branches, all black iron. The piping runs around the perimeter in the basement ceiling, but isn't a complete loop. Instead the headers are connected to the boiler in the "middle", with side connected to 3 radiators and the other connected to the remaining 6 (total of 9, 2 on the second floor). The headers do not taper down in either direction. I personally think it was specified to be full loops but the installers said "screw it" when they had to cross a large opening in the basement wall.

Here's where the weirdness starts: the software is telling me I need *much* smaller piping. Like 3/4" headers, not 1 1/4. Which means my mains are pretty oversized for a pumped system. But the 1/2" risers seem really small for a gravity system according to what I've been able to find here on the site and in some old reference books. Added to that, the software is sizing my pump substantially larger than the Taco 007 that came with the boiler.

So was this originally a gravity system that just didn't need large risers (or an attic tank, etc.) or just an oversized pumped system? House was build in 1944, and the rads are period correct, so it came with the house.

Thanks in advance.

icesailor

The old dead guys had a lot of rules they were taught. Some of the now old dead guys I worked with or for had rules they learned and taught me. They all worked. Some of the rules that are taught to the new, young guys by guys that should have learned something from the old dead guys don't coincide with a lot of things I learned. From the old dead guys.

1/2" IPS mains and branches: 15,000 BTU's.
3/4" Mains and Branches: 35,000 BTU's.
1" Mains and Branches: 65,000 BTU's
1 1/4" mains and Branches: A lot. I don't remember.

If the load was a lot, it might need to be 1 1/2" from the boiler. so split the main into two 1 1/4" mains.

I tried the Flow Pro. I couldn't make it jibe with what the old dead guys and IBR taught me. It must have something to do with those high output mining pumps now so in vogue.

I know it all works.

R2.0

Are those sizing numbers for gravity flow?

I'm reasonably sure I got the heat losses correct.
Heat loss for conditioned spaces: 55.1MBtu/h
Connected Load: 95.3 MBtu/h
Heat loss including basement: 85.1 MBtu/h

While it seems my calculated load is much less than the installed, the house now has double pane replacement windows instead of wooden sashes (unfortunately - at least architecturally). I'll re-run the load changing all the windows to single pane and see what I get. I also back checked it against some of the more simple square foot calculators and they jibed. Flo-Pro tells me I'm at 31.8 Btu/h/ft² upstairs and 42.9 Btu/h/ft² on the main level (cape cod).

The system originally was 1 1/2" at the boiler and split into 1 1/4" for the loops. But the one side doesn't even make it to 30Mtu/h installed. That's why I think it was supposed to be a complete loop

icesailor

Sounds more like it had Monoflow Tees.

That's how we split them up so the last emitters on a loop got enough hot water to heat it up. Listed in the above numbers.

Jamie Hall

That is not a gravity flow system -- it's just a system with larger pipes than one would specify today. Larger pipes, less head loss, smaller pumps.

R2.0

Don't think they are Monoflo tees - they look like standard tees. All the radiators have those weird 180° turn balancing valves. That may be what I mess with tomorrow, balancing the system during the cold snap.

Paul48

Regardless of what the software says..... The Universal Hydronics Formula dictates the gpm based on required btu/h. The pipe sizing charts then give you the minimum pipe size to avoid velocity issues. You will never have a problem upsizing the pipe.

SWEI

32-43 BTU's per hour per square foot after new windows?

R2.0

Yes, with double pane. Reran with single pane:

2nd Floor
Total area 461 ft²
Unit load 35.1 Btu/h/ft²
Total load 16200 Btu/h

Main Floor
Total area 1120 ft²
Unit load 48.1 Btu/h/ft²
Total load 53900 Btu/h

I've also attached printouts from the software.