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Radiant heat

Robert E Lee

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Yesterday I ran into a radiant heating arrangement that I have not seen before. The main floor was heated with copper piping and convectors, however in the basement there is PEX tubing that appears to have been placed below the concrete slab, in the photo you can see that the plastic barrier and concrete slab is on top of the PEX tubing and there is no visible foam insulation below the PEX. This was the only heat source for the basement area. Does anyone think this will do anything more than just warm the floor? I have a hard time believing that it will heat the basement area.

Robert E Lee

Rochester, MN

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The date on the drywall says that the home is less than 8 years old. I doubt if it's PB. I don't think there was anyone in the radiant heating field that was still using PB in 1998. Don't let the color fool you Tom, PEX comes in a lot of colors, including gray.

Robert, I think it will heat the basement but if it is as you say, without any insulation beneath the slab, they'll probably end up using more energy than planned to do so.



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You've touched on a very complex issue that I would like to discuss but time won't allow.

Let me say that at the time of construction the common method was to lay piping on gravel and pour concrete.

Today as we speak radiant systems have become more common, more complex, more design oriented.

Heat loss is calculated -generally by the wholesaler and the piping 'layout' is computer designed, insulation is an option that an uninformed builder would omit.

Anyway, from a home inspection point of view I would concentrate on the following:

Are all the zones responding?

Is the slab thick enough (recommended 4" minimum), I pour 5"

There is a ton of other things to consider but the most important is air changes.

Does the heating sytem provide air changes in the form of a fan/coil or HRV ...?

Your question:

Is this thing going to do more than heat the floor?

The answer:

We would need to know heat loss calculation, boiler rating, flow rates, lenght of zones and their circulator size.....etc. which is beyond a regular home inspection.

If the system is designed accordingly, it will keep the basement toasty warm...the Mercedes of heating. This sytem is now becoming common in commercial space where they could have numerous large commercial overhead doors opening and closing on a continual basis.

I apologize in advance for not responding as I'm currently building a home out of town and have limited time on the puter.

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Thanks everyone. Mike, sharp eye to notice the date on the sheet-rock. The home was built in 1995, the lower level finished off in approx. 2000. There were two heating zones, one for the main level and one for the basement. Anyway I suggested they talk with the contractor that installed the system and that they may need to install copper pipe and convectors to achieve a comfortable level of heat in the lower level.

Robert E Lee

Rochester, MN

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My general view of radiant heat systems is that they are really an 'art form' so to speak and I tell the clients as much.

In other words, there are no two systems alike. Sure, there are calcs that can be performed as RobC outline above, however there is no 'standard' or consistency with their installations. This is based on personal and professional experience.

The concept of radiant heat is the same, but the configurations of tubes, valves, pumps, controls, sensors etc. makes duplication of any one system near impossible.

Guys will install natural gas central forced air systems with their eyes closed- they are almost identical from one cookie-cutter home to the next.

Radiant systems - whole different ball game.

I think 'inspecting' these systems can either be very simple or very complex.

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I just saw same-color PEX yesterday in a hydronic system. (Fittings at copper were leaking BTW). That looks like PEX to me. Next time, wipe off the gravel-dust. The letters PEX are printed on PEX tubing. As for in-slab radiant heat, there are pros and cons. One 'con' is that in some cases, due to the 'flywheel' effect, you can actually overheat the space. I've run into that a few times when folks used in-floor radiant heat and then had huge parties on those rooms. All those 98.6 'heating units on legs' coupled with that thermal mass radiating-off heat lead to the homeowners complaining about having to turn-off the radiant heat.

"Heat goes to where it isn't" is the heating guy credo... Heat from that tubing is radiating full-blast up/down/around, conducting into the soil/gravel/concrete, etc. You get the picture.

It's a case of 'depends on the circumstances" (of install, underlayment of reflective materials, soil composition, installation layout, etc, etc., etc). The orginal poster here may have missed the fact that 'just heating the floor' also 'heats the room' via 'radiant heat' (floor 'giving-off' heat to the other things in the room---including people).

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