Ring Out The Old…

It doesn’t rank with his finest work, but George Harrison did come up with the perfect New Year’s song back in 1974…

Ding Dong Ding Dong” isn’t the most inspired title, nor was the Dark Horse album among George’s best, but hey, it works!

Way back when (Nov, 2009, to be precise) we ran a blog post about the easiest way to boost the surface temperature of a radiant floor heating system (check it out here).

Raising the system water temperature won’t do it, nor will adding more tubing or fiddling with the balancing valves.  The easiest way to boost floor surface temperature is to simply turn up the thermostat.

Radiant floor heating delivers BTU’s to a room based exclusively on the floor surface temperature (click here to review).  A room with a 15 BTUH/SF heating load at a 0 degree Outdoor Design Temperature needs a floor surface temp of  only  77.5 degrees to keep a thermostat set at 70 degrees happy.  Here’s the math:

15 BTUH/SF ÷ 2 = 7.5
70 + 7.5 = 77.5 Floor Surface Temperature

The floor won’t get any warmer than that, simply because the thermostat is satisfied.

When the T-stat’s happy, the zone shuts down. When the zone shuts down, flow to the floor stops. When flow to the floor stops, the floor won’t get any warmer.

Simple, right?

But if you want the floor warmer for that “warm, cozy feet” feeling, all you have to do is turn the thermostat up.

Won’t that make the room warmer?

No way around it.  You’ll use a wee bit more fuel, too.

Lots of folks say radiant floor systems should be controlled with floor sensors rather than thermostats.  Don’t really agree with that.  What would happen if we used floor sensors in the above example, and the floor sensors were set to maintain a constant 77.5-degree floor temperature all winter long?

Remember, the floor needed to be 77.5 degrees in order to deliver the required BTUH per square foot under design conditions (aka – the “coldest day of the year”). And remember, statistically speaking you’re at or near design conditions less than 2½% of the heating season.

So 97½% of the time, the floor will be warmer than it needs to be, so it will deliver more BTU’s to the space than the space needs.  Let’s say it’s only 35 degrees outside. At the temp, the room in question will have a load of only 7.5 BTUH/SF.  Using math from above, the floor would need to be a little under 74 degrees to maintain a 70 degree setpoint.  But since we’re using a floor sensor and maintaining 77.5 degrees in the floor, we’re dumping twice as many BTU’s into the room than is needed.

Floor sensors are best used in a “min/max” mode.  A minimum floor temp setting helps with a high mass radiant system (slabs – click here to review) and big temperature swings.  If the system’s been off all day and the outdoor temperature drops dramatically at night, that big ‘ole slab will struggle to catch up.  A minimum floor temp setting shortens up response time considerably, but the house may be warmer than you want during the day.

A maximum floor temp setting is used with wood floors.  You can use wood floors with radiant, you just have to watch the manufacturer’s recommended maximum surface temperature.  With hardwood floors, that’s usually around 85 degrees.  A max floor sensor setting of 85 protects against little Timmy playing with the thermostat and setting it to 95 degrees, just for a giggle.

You can no doubt see where this thread is going, but you’ll have to wait until next year for the next installment!

And with that, let’s raise a glass to 2011 and bid it a fond farewell…

A beautiful piece of music from the Concert for George.  Did you catch son Dhani playing guitar?  Looks like his dad circa 1966.

2 Responses to “Ring Out The Old…”

  1. In my opinion Dark Horse would come in at #5 behind:
    1. All Things must Pass
    2. Concert For Bangladesh
    3. Living In The Material World
    4. Thirty Three & 1/3
    Saw Harrison in Seattle in 1974 – Fantastic!

  2. I’d say you’re about right, Peter. Extra Texture might be in there, along with Cloud 9…the man gave us some beautiful music. He left us 10 years and 1 month ago to the day…

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