Plated and underfloor radiant without insulation beneath the plates\tubing.

ILikeEmOlder

I’m working with a client to help with high heating costs for their home. The house is in CZ6. Building heat load is roughly 40K BTU/hr at 1F design temp. The 1st story of the home is heated with a mix of underfloor and under-the-subfloor plated radiant tubing. The second story is heated with electric resistance baseboard.

The previous contractor installed the underfloor and under-the-subfloor plated radiant heating, and apparently he did not get a chance to finish the install (due to a “souring” of the relationship with the homeowners).

The PEX tubing was installed in such a way where only portions of the tubing was installed with thin aluminum plates, and only a small portion of the floor has batt insulation installed beneath the tubing.

Thoughts on replacing the thin plates with thick extruded aluminum plates, and adding batt insulation to the entire area where tubing was installed?

The under-the-subfloor section of plated radiant is for the kitchen (with tile as the finished flooring). The basement beneath the kitchen has panel radiators for heating.

The rest of the 1st story has underfloor radiant (with 1/2” engineered flooring on top of the tubing). Would you recommend installing batt insulation under the subfloor as well?

My sense is that it would be prudent to proceed with new plates and insulation under the plates (for the kitchen), and batt insulation under the subfloor for the underfloor radiant.

FYI, I have already sealed the attic floor and added insulation in the attic to roughly R-40. The rim\band joists were already spray foamed, and the basement walls all appear to be spray foamed.

Kaos

Adding heat plates and insulaiton won't reduce your fuel use*. In some cases it improves output and reduces striping. So unless that is a problem, fussing with the existing setup is not worth it.

*Adding heat spreaders and properly configuring a modcon can reduce the fuel use by a couple of % due to lower RWT. Not a big change though.

ILikeEmOlder

Kaos,

First thing I did was change the ODR curve on the boiler (from its original setting for high heat applications, to a setting for mid-range heat applications, and recently to low heat applications). I am confident this will push the needle in the right direction.

What has me a bit puzzled about this situation is the relatively excessive amount of propane used for the heat load and occupancy profile of the house.

Estimated heating energy use is roughly 110 MMBTU. With the existing occupancy profile, expected use is roughly 85 MMBTU.

Currently, the owners inhabit the house only 50% during the heating season, keeping the thermostat to roughly 55F while away. Per their plans, they hope to be occupying the house full-time in a year or two.

The mod-con boiler is a Viessmann Vitodens 100W, and it is connected to a Vitocell 300 indirect tank. This is a pretty efficient setup from what I have gathered over the years. ODR has been enabled from the start.

hot_rod

https://forum.heatinghelp.com/discussion/200930/plated-and-underfloor-radiant-without-insulation-beneath-the-plates-tubing

You are on the right track understanding it is the building that dictates the energy consumption, for the most part.

Building usage also, leaving doors open as an example :)

Blower door tests are the biggest eye opener, as infiltration is a hard number to guesstimate.

Infrared cameras can show where a breakdown of insulation adds to heat loss.

High heating costs are often more about the cost of the energy increasing, additional fees that get added.

You need to know the actual amount of fuel the heating system uses, apart from other appliances.

I've know energy auditors to add a gas meter right at the boiler to get exact numbers.

ILikeEmOlder

Hot Rod,

I couldn’t agree more.

I blower door tested this house, did some IR thermography, and I was pleasantly surprised to see that the house was performing fairly well before I got to work on it.

I’m perplexed by the amount of actual heating energy use versus projected use. 110 MMBTU (estimated) heating energy used last year, but projected is as low as 85 MMBTU.

Infiltration has been reduced with the attic air sealing, and we are already seeing benefits from adjusting the ODR curve to reflect the radiant floors, but heating energy consumption is still quite high for this particular house.

Kaos

Is there a readiant slab in the basement? Lot of those out there, especially with a walkout, where the slab is not isolated properly and lot of the heat is lost to the soil/outdoors.

If the fuel use is above what the blower door backed up energy model says, the heat is going somewhere outside the house or the energy model is off. I've seen a lot of shabbily insulated walls out there, so an R19 wall might not be anywhere near that.

ILikeEmOlder

Kaos,

Good questions and good points.

I will revisit the model.

I traced the entire distribution system from the boiler. No other emitters other than those I mentioned for the basement (two panel radiators).

I can see spray foam on the tops of the poured foundation walls, and spray foam is readily evident at the rim\band joists.

The IR camera shows insulation in the framed walls (2x4 construction), and insulation in the ceiling above the kitchen.

There are the typical weak spots in the insulation, and a decent amount of air infiltration, but no “****” moments yet.

Thanks for your thoughts thus far!