Radiant + Forced - Help!!

rwinch

Hi all. Please bear with me on this one. We bought a log house in NH this summer (with vaulted ceiling). It has radiant floor heat (4 zones) and forced hot hair (1 zone for whole house).

I don’t have any info on how to set things, so I’ve been experimenting, but it’s not going as I expected. I set the floor thermostats to 68° and the air thermostat to 66°, thinking that would keep the floors warm and the air would not come on often. But at some point, the floor circulators stay on all the time and the house never warms up. Do I need to increase the temp of the water in the floors? I was told that part was just “set it and forget it.” It’s a Viessmann Vitodens 200W if that helps. Thanks in advance for any advice!

Jamie Hall

Actually, that's an arrangement which can work pretty well -- once you get it properly controlled.

Step 1 is to get it so that the floors can hold a temperature. There are two considerations here. The first, and perhaps a little less obvious, is what temperature can the floors, in fact, hold without toasting your feet. Hopefully it will be at least 65. The objective with floors is that they should be running pretty much all the time, as yours seem to, and the water temperature going to them needs to be adjusted up -- or down -- to suit. Does your Vitodens have outdoor reset, if so, that should do the adjusting for you.

Does it also have a temperature gauge? Hopefully two -- on on the pipe leaving and one on the pipe returning. What do they read?

Having multiple floor zones is useful only in that you can adjust the flow in each to maintain the temperature you want in each.

What you can't do with radiant is run the temperature up and down -- such as trying to use setbacks. Radiant floors just don't respond fast enough.

So -- that's where the forced air comes in. If you can run the floors so that they hold a nice minimum temperature in the space -- whatever is comfortable, but perhaps 65, then you can use the forced air to boost the temperature when you want it wormer. Forced air responds quickly, so just crank up the thermostat for the forced air...

rwinch

@Jamie Hall Thank you for the help! The settings on the unit, combined with the zone thermos, are what have me confused. But I think: each zone thermo tells the system whether or not to circulate the floor water in that zone, and the system itself is just constantly maintaining the water at temp X (mine seems to be set to 66°). But I also see "Boiler temperature 99°". That must be the temp of new water being added when it drops below 66°?

If all that is correct, then my floor system is saying whenever temp in Zone X drops below set pt, circulate the water (that is, in this case, set to 66°)

As an experiment, I tried turning that up to 70° thinking I'd for sure be able to feel it in the floor, but I can't. It's probably working fine, but balancing the floor temp setting vs. the air handler temp setting is challenging. I'd prefer the air is not on unless really needed. It's loud and dry.

Any further thoughts/suggestions/learnings would be greatly appreciated!