Variable speed pumps

Simply Rad

I installed a Grundfos Magma 32-100 pump for a full house radiant floor system and I am amazed how little energy is used to distribute so much heat! The system is currently pump 16 GPM@ 13' and is ONLY using 63 watts!!!!!!! This is incredible. These pumps are huge energy savers considering I am using continuous circulation distribution. The home is 10,000 ft2 with a heat loss of 160,000 btus. Amazing to think an old school 100 watt light bulb uses more energy than the system pump. Also, something to consider is the fact I have been using the Viessmann Vitocrossal CU3A medium mass boiler that I use direct pumping. Meaning, the pressure drop is so low, non restrictive and has 20 gallons of storage, that I am using one pump for the radiant floors and one for the DHW. Super simple and highest efficiencies since there is no mixing the return water....direct return. I love this boiler and system

Cheers Jeffrey

kjb1057

Right on! Your a very smart individual

hot_rod

Nice work!
It's nice to have access to all that data also.

I sent you a couple PM about that radiation sensor, not sure you received them?

Shahrdad

Jeffrey, how many BTU's does your Vitocrossal have? I have a 123 year old house with an old gravity system and a 1970s cast iron boiler (196,000 BTU output), and I'm considering changing to the Vitocrossal. Could you tell me more about your system? I have cast iron radiators that are lukewarm most of the winter and the house stays very comfortable. I know the biggest Vitocrossal 300 CU3A has an intake of 199 BTUs, which at 95% efficiency should be an out put of around 190K BTUs. I think that should be enough for my old house, but not totally sure. I see contractors installing huge boilers for houses way smaller than mine in my neighborhood, and I don't want to go that route.

Jamie Hall

It might be better, @Shahrdad , to start your own thread. Your question isn't really about variable speed pumps, after all, but replacing a boiler -- a very very different project.

That said, you are clearly guessing at what size boiler you might need. There is only one way to determine that: do -- or have done -- a Manual J heat loss calculation for the house. Slant/Fin has a very nice calculator here: https://www.slantfin.com/slantfin-heat-loss-calculator/ which is remarkably accurate -- and easy to use.

You are quite right in thinking that too big a boiler isn't a good idea. In fact, it is a financial catastrophe. Do it right.

Robert_25

I installed Grundfos Alpha circulators in my system this fall.  I have been very surprised at how little power they use.  I think lots of systems are over pumped.