Head loss calculations.

Tonerlow

Need some help with circ pump sizing. What is the head loss in a radiant heat system on a 1250 sq ft slip level bungalow with fin tube radiators, 3/4” copper lines?
House is 30x40 so 140’ per run? (One zone upstairs one downstairs)

google says 140*1.5*.045= 9.45 ft head loss ? Is this close ?

Jamie Hall

Maybe. What's the flow rate, in gpm?

Tonerlow

@Jamie Hall Veissmann 200w B2HB 94. Manual says max flow rate 6.2 gpm.

The boiler pump is a grundfos UPS26-99FC. This pump shows much higher flow rates than 6.2. So this is where I am confused.

Tonerlow

Jamie Hall

Keep in mind that a pump — any centrifugal pump, whether it's called a circulator or a boiler pump or whatever — has a variable flow rate depending on the head it's developing.

The Viessman flow rate rating is controlled partly by the velocity through the boiler, but also by the design temperature rise going through the boiler — and it is best to abide by that. And it is, within reason, a maximum, not a target.

The flow rate through your system is related to the power being delivered to the structure. The power delivered, in BTUh, is equal to 500 times the delta T between the beginning and end of the circuit times the flow rate, in gallons per minute.

GroundUp

Approximately 5ft of head with 140ft of 3/4" type M at 4 GPM with 150* fluid. But what you're actually flowing is entirely dependent on the rest of the system. The 6.2 GPM rating from the boiler is likely just a rating at a given pressure drop and means nothing without more information

GGross

I believe they are using a larger pump in an effort to avoid primary secondary piping. That boiler is a flow dependent boiler, generally it would be best to pipe it primary/secondary, and have a separate circulator for the heating system. The correct boiler pump for that boiler would be a grundfos 15-58, but if it is direct piped you might not get enough flow through the system to make the flow switch, as you are also overcoming the pressure drop of the heat exchanger, in addition to the piping system.

What problems are you having that brought you to ask about this, and can you post some additional pictures of the install, just want to make sure this is indeed direct piped, and not piped correctly

Tonerlow

@GGross You are correct that this is piped direct. Mostly I am here trying to educate myself in order to convince the plumber to repipe this.

Ie: install manual states “If flow rate is out side of these parameters, or NOT KNOWN. VEISSMANN strongly encourages the use of a LLH”

I’m trying to get my facts straight and backed up with some tangible data.

Tonerlow

@ggross also as is being discussed on the other thread, we have a cold bedroom which I suspect is at least partially due to inadequate flow. There is a ball valve being used as a bypass to allow the boiler pump to run continually. When the zones are calling for heat I can fiddle wth that valve and the sound of the glycol flow will change based on position of the bypass valve. This makes me suspicious that there is too much fluid passing thru the bypass rather than making the full run through the baseboard radiators. This is indeed why the pump was upsized from a 15-58 was to try and achieve more flow with the current piping @GGross

Tonerlow

better pic @GGross

mattmia2

Is it radiant or is it fin tube?

Tonerlow

@mattmia2 this is all 3/4” fin tube radiators.

mattmia2

Fin tube baseboard doesn't have a lot of resistance, it can probably work off the boiler pump if one is careful with their math. Much more likely a problem with air if part of a zone heats but part doesn't. Can also balance it using the dampers on the baseboard housing.

hot_rod

What supply temperature do you have set in the ODR. Maybe just a bit more temperature would resolve the issue.

If you do need to pipe it P/S you will have some temperature blending and may need to ramp up the temperature.