Programmable t-stat for NON-SLAB hydronic radiant?

Rossputin

Hey there, heating experts,

Thanks in advance for any advice on this.

I've read a lot of posts from folks who recommend against using programmable thermostats for radiant heating and I wanted to see if our specific situation changed that recommendation.

We have a hydronic radiant system with a bunch of zones and the setup is Pex pipe running through the center groove on aluminum transfer plates which are screwed directly to the subfloor, which is whatever standard thickness wood would have been used in building homes 30 or 40 years ago, and then there's approx 1/2"-thick LVT on top of the subfloor. There is no other material between the transfer plates and the floor except for a section of the kitchen where we had to use some self-leveling material (that looks like concrete but apparently isn't concrete.)

It seems to me that when the heat goes on, the floor warms up fairly quickly, like less than 30 minutes, though I can't say I've timed it. If an expert here wants me to time it, I'll do that.

Anyway, given that situation, and not wanting my natural gas bill to be higher than it needs to be (and keeping in mind that my boiler is almost 60 years old and while it's built like a tank it's not the most efficient thing), do you experts think that a programmable thermostat (perhaps one that can learn how long it takes to get to temp in a room, although I can probably just figure that out myself) would make sense to save on my heating bills while also having my home comfortable during hours that we're awake (and home)?

Thanks!
Ross in Denver

Ironman

No, that's not the solution. What supply water temp is going to the floor? You need a proper mixing device to control the SWT.

SuperTech

It does sound like you are heating the water too much or have your outdoor reset curve set wrong. The best possible comfort is the goal of radiant heating. That's achieved by matching the heat loss with the heat produced without a lot of cycles.  Using a programmable thermostat doesn't play a role in that.

Rossputin

I think water is around 170 degrees. Same boiler heats one remaining baseboard heating unit along an edge of the house where we couldn't reasonably install radiant. The installers said I did not need to mix down to cooler temp water though I don't remember why.

I'm unclear on why, if the system heats up fairly quickly, it wouldn't make sense to slightly lower the temperature at night rather than keeping the room at the higher comfortable temperature. We're talking about something like 3000 sq ft being heated this way and I'm concerned about my natural gas bill being horrendous.

Ironman

170* is way too hot for a radiant floor! It will ruin the wood floor if you continue to operate it with that high of a water temp. 125* is the normal max SWT for a wood floor.

I don't know of any kind way to to say this, but your installer doesn't know what he's talking about. You need a mixing device/control installed to get the SWT down to where it should be. The flooring manufacturer won't guarantee the floor with water temps above 125*

Also, the hotter the water temp, the less efficient the system will be.

I'd recommend a Taco smart mixing valve with Out Door Reset or a Tekmar variable speed injection mixing control. Either one will also provide boiler protection too.

To be honest, a 3000 sq. ft radiant floor should of had a new mod/con boiler installed with it where it would operate at 95% efficiency instead of 50 -55% efficiency which that old boiler is operating at. That's where you're wasting gas. The mod/con would also have ODR built into it so you wouldn't need a separate mixing system.

I would have never installed a large radiant floor like that and then connected it to that old fuel hog.

SuperTech

All of the above sounds correct. It seems like you have the wrong boiler combined to a terribly designed installation. It doesn't sound like the installer is familiar with radiant heating. Maybe try to find someone who more experienced with radiant heating and have them try to salvage something from the current system.  

Rossputin

Wow. So they told me that because the flooring is LVT rather than wood, the current temperature is OK. Separately given that the floor heats quickly with no concrete between the transfer plate and the subfloor and then the flooring, do you still say no to using a programmable thermostat and lowering the temp overnight?

infloorradiantheat

I am not a pro, but a homeowner who has had radiant heat in Denver for a couple of decades. I think in your situation I would install a programmable thermostat. We don't have programmable but I change the set temperature at will. There is no harm to a programmable thermostat. The only reason they advise against it is the delay in heating up the house from cold if the floors are well insulated under carpet or hardwood. If your house heats up fast enough for your satisfaction then programmable is the way to go.

I'm surprised that the tubing you have can tolerate that much heat. But our tubing is old and an old hydronic's expert once warned us about hitting it with straight boiler temperatures in the event of a failed mixing valve. He advised we put a thermostat on it that would shut off the supply if the heat got too high. In our redesign we got mixing valves that said they failed into the off position instead of full open (at least that is what my memory says was our solution). May not have helped us when we accidentally left the floor on in Sept. after a cold night and then turned the AC on during a hot day. At some point the water probably rose to around 180F before we discovered our error.

We proactively replaced our old boiler before it failed due to some parts on it rusting out and a worry that it would fail at an inopportune time. When we looked into modulating boilers they seemed to have alot of errors, breakdowns and shut downs. When our house was evaluated we couldn't install one any way as there was no way to vent it. We ended up with a new higher efficency cast iron boiler. I hate that thing with a passion. It took a full year before it operated for longer than 2 weeks in a row without going into an error state. The installers replaced everything on it. The other problem is it has an active vent fan that is NOISY and vibrated our whole house. The installers worked hard on isolating the vibration, replacing the fan assembly etc. I can still hear it upstairs if I am in the right place in the house and it is quiet but at least I can't feel the walls vibrate. The old one was quiet and had no exhaust fan. My old one hadn't failed yet but had some rusting out components so we had it replaced. If I could go back in time I would never have proactively replaced it until it was fully failed on it's own.