Forced air and hydronic in-floor heat

Tarzank7

Everything I have seen that closely resembles this topic has been a mix of responses and does not seem to give me answers to my exact situation. I am wanting to understand the best way to control the of use radiant floor heat as the main heating source for my house, and using forced air for the AC (and a possible heat back up).

Here are my desires: I want to use a gas powered boiler for heating, and a gas powered furnace (forced air) mainly for cooling. I want to heat my basement, garage, and main floor with radiant floor heat and the third floor with forced air. I will also want to cool the main floor and third floor using forced air. Without having to use separate thermostats

My questions: Is there a thermostat that can handle this situation and keep the two appliances from fighting one another? I have read that Tekmar is a good one to go with radiant floor heat, but will it work with forced air and in floor heat? Or would something like a nest be just fine for this application?

Thank you

mattmia2

You would want something more like a BMS to control two heat sources off the same thermostat. Since you are already making hot water you could use an air handler with an AC coil and a hydroair coil for the cooling and supplemental heat instead of having additional fuel burning appliances at each air handler location.

EdTheHeaterMan

I have had a similar problem and tried a thermostat that had 3 stages for heat and 2 stages of cool. I used a 2 stage gas furnace with a 2 stage condensing unit for my one story home. I could not get the spread far enough apart to keep the furnace from operating when the radiant could do the job but was just a little slow to respond when the outdoor temperature dropped too quickly. After 2 years of adjusting different parameters on the boiler and the thermostat.

I gave up. I finally ended up with a Nest to operate the AC and the Radiant boiler and a separate thermostat for the gas furnace. When the outside temperature was lower than 17°F the radiant could not keep up. When that happens, I just set the radiant to 75°F and set a separate furnace thermostat to 68° or 70° (whatever the girlfriend is comfortable with) until the Outdoor temperature is above 17°. Then I would put it back to normal and the gas furnace would not operate.

You would think that if they can put a man on the moon you could make a thermostat that does what I want it to do.

And Who is THEY anyhow?

mattmia2

They do, i t is just commercial and usually only used on larger buildings because they are the only ones that can find someone to set it up properly.

Doug_7

We have a similar situation to control the in-floor heat, forced air heat, and air-conditioning for a single large residential space.

We use a Honeywell THX9421 Thermostat, which has Two-stage Heat and Two-stage cool, installed centrally.

The first-stage heat is the in-floor heat. The second-stage heat is the forced air heat. The two cooling stages control the air-conditioning. Works perfectly.

This Thermostat has a Remote Equipment Module that the Thermostat talks to over 2 wires. The heating and cooling equipment is all wired to the REM.

The temperature "gap" between the heating-stages can be set and adjusted. We have it set at 1.5º F which works perfectly, but could be set higher or lower depending on your requirements. The first-stage heat provides the heat 99% of the time, The only time the second-stage heat really comes ON would be recovering from a deep setback - which we avoid except for vacation-setback.

Other separate spaces, like the garage, would need separate, simple single-stage heat thermostats for heating only.

The Honeywell THX9421 Thermostat also controls ventilation. You set the area of the space and the ventilation system capacity and the Thermostat does the rest to meet the ASHRAE Ventilation Code.

Touch-screen Thermostat is easy to program - just read the manual.

Tarzank7

Thank you for your responses and the types of thermostats you are using for this type of set up. I really appreciate it.

In a two stage heat setup (say the boiler is stage 1 and the furnace is stage 2). Could a floor sensor be used to communicate to the second stage saying there is heat keeping stage two from running?

hot_rod

Do you have ways to damper off the FA?
how will it heat only one level but cool multiple areas?

HVACNUT

Doug_7 said:

We have a similar situation to control the in-floor heat, forced air heat, and air-conditioning for a single large residential space. We use a Honeywell THX9421 Thermostat, which has Two-stage Heat and Two-stage cool, installed centrally. The first-stage heat is the in-floor heat. The second-stage heat is the forced air heat. The two cooling stages control the air-conditioning. Works perfectly. This Thermostat has a Remote Equipment Module that the Thermostat talks to over 2 wires. The heating and cooling equipment is all wired to the REM. The temperature "gap" between the heating-stages can be set and adjusted. We have it set at 1.5º F which works perfectly, but could be set higher or lower depending on your requirements. The first-stage heat provides the heat 99% of the time, The only time the second-stage heat really comes ON would be recovering from a deep setback - which we avoid except for vacation-setback. Other separate spaces, like the garage, would need separate, simple single-stage heat thermostats for heating only. The Honeywell THX9421 Thermostat also controls ventilation. You set the area of the space and the ventilation system capacity and the Thermostat does the rest to meet the ASHRAE Ventilation Code. Touch-screen Thermostat is easy to program - just read the manual.

No floor sensor for the radiant with that, which is a deal killer for most. Otherwise it's a great thermostat. 
The OP could always go third party, like Crestron or Savant.

Doug_7

In a two-stage heat setup with your boiler as stage 1 and your furnace as stage 2, you would not want or need a floor sensor to communicate to the second stage saying there is heat keeping stage two from running. Totally unnecessary and far too complicated. The Honeywell THX9421 Thermostat can do it all.

The temperature "gap" between the two heating-stages is all you need. It can be set in 0.5º increments up to 3º F. That is all you need and this the best way to delay the second stage Heat from coming ON until you really need it.

We have a high-mass in-floor heating system - PEX in Gypcrete - so the temperature of the space is very stable and slow to change. So the temperature "gap" between the two heating-stages is set relatively low at 1.5º F and the second-stage heat virtually never comes ON - which is what we want. But the second-stage Heat is there if really needed.

We have the "gap" set at 1.5º F which works perfectly for us, but could be set higher or lower depending on your requirements. The first-stage heat provides the heat 99.9% of the time. The only time the second-stage heat really comes ON would be recovering from a deep setback - which we avoid except for vacation-setback.

When the warm weather comes along, the Honeywell THX9421 Thermostat will seamlessly switch from Heat to Cool. There is a minimum 3º F gap between the Heat and Cool settings which I think is required by Code.

Basically you want a central Thermostat capable of two-stage Heat and Two stage Cool. Separate Heat-only Thermostat for the Garage.

Doug_7

HVACNUT - No floor sensor is required for the radiant with this thermostat. The Honeywell THX9421 Thermostat does it all - it works perfectly.

Tell me why you think you need a floor sensor and why you think it is a deal killer ??

Crestron and Savant are whole-house automations systems - overkill.

pecmsg

The floor sensor does exactly that measure the floors temperature. With outdoor reset it knows at what temperature outdoor the floor needs to be.

Doug_7

We use Outdoor Reset to control the temperature of the Floor Heating Water.

All done in the boiler room. No floor sensor required.

pecmsg

The floor sensor is still more accurate!

Doug_7

OK - different system design and different control philosophy.

Temperature control on our floor-heating water is plus or minus a degree or two, which is good enough for me, and controlling the floor-heating water temperature is a very simple way to do outdoor reset - but use a floor-sensor if you like.

The original question was: Is there a thermostat that can handle this situation and keep the two appliances from fighting one another? I tried to answer that specific question, in recommending the Honeywell THX9421 with two-stage Heat. I know this works great because that is how we have done it for years.

So back to the original question - What Thermostat do you recommend, and how would it interact with the floor-sensor ? I am interested to learn.

HVACNUT

Doug_7 said:

We use Outdoor Reset to control the temperature of the Floor Heating Water. All done in the boiler room. No floor sensor required.

Neither the thermostat sensing air, nor a floor sensor controls the temperature of the heating water. Of course a floor sensor is not required, but ask contractors who do radiant work every day what's best. I'm just a dumb service guy.

Tarzank7

Doug_7: Thank you!! I read your first comment that suggested that thermostat but just had the question in my head about a floor sensor. I know floor sensors are typically used to control the comfort level of the floor, not really the air, but wanted to ask to see if anyone has used a floor sensor as a "thermocouple" per say. But it sounds like that thermostat can do it all.

Doug_7

Hi Tarzank7 - You are welcome. The Honeywell THX9421 Thermostat can do it all - controls first and second stage Heat and Cooling.

There will be other makes of Thermostats out there with first and second stage Heat - but this is the one we use - and it works great.

A bit pricey so shop around. Download and read the Manual so you understand it.

hot_rod

What type of boiler? If you have a boiler that can accept a 0-10 signal, some thermostat can modulate the boiler based on indoor temperature feedback. Tekmar calls it room response. This can be helpful on applications that see solar gains or have high internal gains or super insulated spaces.

Floor sensors just add one more control input. So it could add a bit more comfort control, or be used as a floor covering protection, limiting the slab temperature at high demand or below design conditions

But I’m still not clear how the radiant heats two levels, the furnace just the upper level. But it cools all three levels. If it runs to heat the upper level, how does it not overheat the radiant levels? Unless it has zone dampers?