Reducing costs w/my horribly inefficient floor heat boiler

[Jim Caudill]

I tried several different ways to make my underfloor heating more economical; the only one that worked was shutting it off, period. A 500,000btu boiler will use aproximately 5ccf or 5 therms per operating hour. Depending on where you live, you either buy ccf's (me) or therms (lots of other places). Take a look at your last winter gas bills and see what you paid (per ccf or therm) with all charges and taxes added together. If you paid $2, then your heater will cost you $10per hour in natural gas while the boiler is actually firing. You can play with slabstats, dual thermostats, return line sensing all you want, but at my wash, once the temp falls below about 20degrees, you're all-in, all the time. The only thing that you're being regulated by, is the limit switches.

If you spend most of your winter above 20 degrees, then some of this stuff may work for you. When it gets cold, it really doesn't matter- you're going to "pay the piper". I don't get enough winter revenue to make it practical to heat the floor anymore.

 

[Waxman]

Jim C:

What about the cycle timer idea for when you're 'all in' as you say. If it were on 15 min. then off 15 min, wouldn't you cut your gas bill to $5/hr from the $10 you said?

 

[Earl Weiss]

I would think that instead of cycling based on time which depending on outside temp could mean the floor heat never gets to the point where heats the floor to above 32 degees, the only way to make sense is to have the burner tierd to a switch which keeps the fluid above 32 degrees. Once it drops below that it's worthless. Or in other words if you cylce as suggested and it's 20 degrees outside or less , theoreticly during the Off cucylce the temp could dropp to 20 degrees or less. During the on ccycle it may never reach 32 degrees and therefore be worthless.

 

[Waxman]

I understand somwehat, but this is getting a bit complicated for my brain.

 

[Dirt]

This has got to be the ticket. Got me to only 500+/- gallons of heating oil per year for 2 ss bays. Made by Heat Timer Corp.

 

[Waxman]

Dirt

Where are you located?

When did you install this? Overall cost to install?

Thanks!

 

[Dirt]

Hi Waxman, it's Dirt.
I'm by Pittsburgh. 15062.
In 2000, when I tore my bays out of the ground and rebuilt them,I built, and partially designed, my floor heat system.
I could dig up actual figures, but you mays well figure about 300 for the RSM, probably 150 for the motorized mixing valve, a couple immersion wells @ 20, sensors come w/ the RSM (3). $600 would probably get you there.
What ya think? Pretty cool, huh.

 

[Waxman]

Super.

Can you describe how this works and what it does?

Thanks!

 

[Dirt]

Well, the RSM (Residential Snow Melt) controls the motorized mixing valve. I assume that all systems have some kind of mixing valve. I mean, I don't think anyone shoots 200* fluid directly from the boiler straight thru the floor. There are 2 loops. The boiler loop, and the floor loop. When the valve is closed, all floor fluid goes directly back into the floor. None is taken from the boiler loop. When you start to open the valve, the floor loop starts to "steal" hot fluid from the boiler loop. If the valve is fully open, then all boiler fluid goes directly to the floor, acting as a single loop.
Anyone can manually adjust a mixing valve to control supply temperature to the floor. Good thing here is, the RSM does it constantly, and with much more precision than a human can do it. Heres how:
The RSM moniters three variables. Supply temp., return temp., and outside air temp. (no slab sensor needed).
Depending on what your settings are, the RSM adjusts the mixing valve to control the temp. of the slab based on return temp. and outside air temp.
Colder - more heat. Warmer - less heat.
And, it even turns the system off for you. My cutoff is 37*.
Therefore, your slab is always at the minium temp. (just enough to melt ice), and absolutely no energy ($) is wasted.
I hope this helps, and happy carwashing!

 

[Waxman]

Super; thanks.

Now I just have to find someone competent enough to install one.

 

[Dirt]

If you can sweat copper together, then you can easily install it.
Although it does matter where you put what.
If you need any help, let me know.

 

[Dirt]

UPDATE!
Used 700 gallons of diesel (heating oil).
$1,500.
For 2 bays and apron.

 

[PaulLovesJamie]

UPDATE!
Used 700 gallons of diesel (heating oil).
$1,500.
For 2 bays and apron.

Dirt - over what period of time?

 

[Dirt]

Nov. 15 thru March 15.

 

[Waxman]

is this due to the automatic thermostat device you had installed?

what savings does that represent over same time period for previous year (or when you didn't have the device)?

 

[Dirt]

Never ran the system without the RSM. This year was a little higher than last year. Thats for 1140 sq ft.