How to manage radiant and forced heating

JohnWT

Hi, new user.


We have just purchased a house that has radiant and forced air. On grade slab with radiant, second floor radiant on joists with a separate zone as well as forced air for both floors on a third zone.

3 Thermostats, 1 for ground floor radiant digital non programmable, 1 on second floor for radiant digital non programmable and a 3rd on the ground floor for forced air analogue.

5 year old house, good air tightness, insulation and windows.

Any thoughts on how best to drive the heating system? Maybe set radiant on ground floor at 71F and forced air at 68F so the radiant does the heavy lift and the forced air only acts as a supplemental if the radiant isn't getting the room to temp.

Any suggestions on a smart or clever thermostat system than the current mix of digital and analogue non programmable thermostats,

John

EzzyT

The radiant should be the primary and the hydro-air as the secondary/supplemental. 

Primary radiant thermostat set at desired temperature and supplemental hydro-air thermostat should be set a few degrees below the desired temperature.
Ive installed a lot of Honeywell T6 and T10 smart thermostat with great success.
The T10 can have remote  wireless sensors connected to it.
Both have the capability of wifi connection.

Zman

Do you have outdoor reset on the radiant water temp. Are slab sensors a possibility?

JohnWT

No outdoor or slab sensors as far as I can see and the radiant is hydro. I'll take a look at the Honeywell T5/10, thank you

GroundUp

What's wrong with leaving it alone? Set the radiant where you want it to be and set the forced air a few degrees below that for backup. All done. Trying to use both simultaneously without slab sensors is going to be a neverending battle

JohnWT

Its a new to me house so no idea of what the current configuration is or what to leave alone. As i posted above I was planning to set radiant a degree or 2 higher than forced air, just wanted to check that wasn't stupid, it seems its not.

pecmsg

If you desire any type of nigh setback's then the in floor needs to be second stage with the forced air as primary.

hcpatel78

I have similar setup in my house. I have Tekmar thermostat with floor sensor separately installed besides forced air (now I used as a supplimental only) thermostat.
I keep my radiant floor set at 70 . Which is good not go beyond 80F for wood floors. It keeps room air temp at nice 68+ F.  I also keep my forced air at same temperature 68 set. So when it's too cold outside(around below 20F) my forced air turn on in morning to bring set room temperature. Once that is achieved , my radiant heat keeps up the temperature for whole day as days get warm as sun comes out.
I don't do night setback for radiant but I do setback at 55 for forced air at night when I am not using that perticular zone at night.

I keep my radiant  at 70 set and forget for whole season.

I also have outdoor reset for my mod-con boiler, which sets my radiant heat supply water temperature efficiently.

That works for me perfectly.

Mike_Breault

@hcpatel78 Mike Breault from tekmar here, rather than 2 seperate stats, why not use a tekmar 562 qand set second stage as FA/ AC / Fan operation se the differential to 2°F and a time limit, and consolidate into one stat?

Best

hcpatel78

@Mike_Breault Hi Mike...That will be perfect solution for this setup. I did not think to combine this as for me...I wanted to keep simpler....
(1) It will be very cumbersome to fish wires for new T-stat for the radiant in finished wall from basement to my next level living room.
(2) I don't someone in my family to crank up the Floor Temperature accidently for my wooden floor and damaged wooden floor.
(3) I set up radiant T-stat in basement with floor sensor near by manifold and Relay so don't have to run long wires. I keep my radiant set and forget at define temperature(70 F). Also I don't want to spent money on sophisticated expensive T-stat solution. If I have new construction going on then definitely consider that.
(4) in my forced air I already spent $xxx.xx for my Nest 3rd gen T-stat and I did not get even few years of usage out of it.

Pewhite22

Hi @JohnWT - I know this is an old post, but I'm putting together a similar system at my house right now. Currently I have a Nest Learning Thermostat (their highest end one) wired with the radiant as stage 1 and the forced air as stage 2. In the Pro set up, you can tell the Nest thermostat what type of heating it is and what the fuel is. It seems like for the Nest with the radiant as the stage 1, it defaults to keeping that on as long as there is a call for heat. If it senses it's getting a little cold and the radiant isn't keeping up, the radiant stays on and the forced air gets turned on for a little boost. This is exactly how a radiant floor system and a second stage heating system should work. You don't want the radiant turning off because the floors are slow to heat back up. Your set up is a little funky because it sounds like the forced hot air is one zone for the entire house. You could try connecting the forced hot air as stage 2 heating to two thermostats, but that might get wonky if they're fighting each other. For this to really work, you'd want some kind of switch that would default the furnace as the stage 2 for the first floor thermostat during the day and then at night switch to it being controlled as the stage 2 for the upstairs thermostat. This is definitely doable and potentially pretty easy depending on how many wires they ran to each thermostat and how comfortable you are with a little wiring. A Shelly or Sonoff wireless smart switch would do the trick. The better (but more expensive) thing to do would be to zone the forced hot air so the dampers are controlled by a first floor and second floor thermostat. 

Dave Carpentier

FWIW, we have in-floor on the main slab and then an air handler for the second floor. We put ceiling returns only in all the rooms on the main floor. I think its helpful to have some kind of air circulation, and thats the one thing missing with in-floor. We run our air handler in fan mode for most of the year (oh the money I would have saved had I put a more efficient blower motor in there 20yrs ago..)