BTU Calculation

I'm not so sure a tank-less would be the best choice for your application.

From what I've read about the tank-less water heaters, they are a demand type of appliance, not intended for closed loop operation. Inlet water temperature is normally 50-60F with outlet being normally held to 120F max.

Think about what your inlet and outlet temps will be in closed loop operation when the building reaches optimal temperature, and then look at the specs for the most common tank-less heaters. My experience in installing closed loop systems is that your boiler outlet temperatures are usually set around 180-190F, higher than a tank-less is designed for. I could almost guarantee you would not get the performance you are looking for.

My advice would be to look into a small boiler or tank type water heater. If you have propane or natural gas available that would be the most economical choice for commercially available fuel, or you could look into bio-waste fueled options.

Good luck!

From what I've read about the tank-less water heaters, they are a demand type of appliance, not intended for closed loop operation. Inlet water temperature is normally 50-60F with outlet being normally held to 120F max.

I intend to cause the thermostat to switch the circulatory pump activating the tank less heater.

The models I intend to use are processor controlled, in that the input temperature is known to fluctuate and the device will automatically adjust the use of four elements to the required temperature gain while maintaining and out put temperature adjustable 110° to 170°.

The result of BTU calculation supplied by the electric company 13,500 differs immensely from the recommended BTU 105,000 of the plumber.

Having given the pertinent info I am of hopes a recommendation can had that more reasonably reflects a comparison of the mathematical sum.

Thanks

Man Bravo you are something. Not my field but I've saved your calculation, will help me out someday when I do come across something like this.

Please please explain me :

The inverse of R 40 is 0.025 Btuh/ sq. ft. degree F .

What do you mean by inverse? What is R 40? and how to arrive at Btu/h value?

Similarly same questions for:

(a) The inverse of R 25 is 0.04 Btuh/sq. ft. degree F .

(b) The inverse for R 11 is 0.09 Btuh/sq. ft. degree F .

(c) Assumed R value for doors based on foam insulation value of R 5 per inch at a thickness of 1.5". The inverse fo R 7.5 is 0.13 Btuh/sq. ft. degree F .

Please assume me here as a fresh high school. For my crave for learing I'd bow to any level yet not feel at all

An R value describes the resistance to heat transfer of a material. To find heat transfer through an object (the direct opposite of heat transfer), the R value is inversed. An R value of 40 would have a heat transfer value of 1/40 or 0.025. Similarly, a heat transfer value would be inversed to find the R value.

I have left the units off the R value. Heat transfer values have units of Btuh/sq. ft. degree F. As the numerical values are inversed so are the units, so an R value would have units of sq. ft. degree F/Btuh. I hope this helps.

THANK YOU ALBINO MOOSE NOW I CLEARLY UNDERSTAND AND THANK YOU FOR TEACHING ME SOMETHING NEW.

.33 to .35 ACH respectively yes. Basement is R10 underslab/vapor barrier and in floor heat via dual zone tankless heater; one zone for slab one for radiators, R40 walls no exterior doors.

I agree air change estimate was high as I did not have any references in front of me. I did question the R value of the window as I was writing out the example but decided to leave it since I wished only to show how to calcute the heat loss.

I sit corrected

Thank you for contributing (:

I know I'm a little late to the thread but I'd like to add one more comment. Albino, I agree your example works well to demonstrate the method for calculating heat loss. However, one must be careful to use the actual equivalent R-value for the entire wall, ceiling, floor, etc, when taking the inverse to use in the heat flow equations. I will use U-factor to be the inverse of R-value.

For example, here in Oregon the basic residential energy code requires R-21 wall insulation. Out of convenience this is called an R-21 wall. The equivalent U-factor required by code is U-.060, which corresponds to just an R-16.7 value. Therefore, when doing the heat loss calculation you would use U=.060 not the .048 number one would get from taking 1/21.

The reason for this is that the wall assembly contains framing members which conduct heat much better than the cavity insulation. These thermal "shorts" act to reduce the overall R-value of the complete wall.

In the example given here, we can use ASHRAE methods (parallel path in this case) to determine that a 2x6 wood frame wall with studs 16"OC, with 1/2" sheetrock and siding over R-25 cavity insulation would have a U-factor of .056. Which is to say the whole-wall R-value is only R-17.9 (1/.056=17.9) This includes the inside and outside air film resistances.

So the true heat loss through the walls would be nearly 30% more than shown in your example. A similar calculation could be done for the ceiling.

If anyone reading this has experience calculating U-factors for light gauge steel frame construction please contact me!!

The windows are a well with dual dual panes opposed by 5" free air. when exterior temp falls below zero I will close exterior insulated shutters and interior insulated shutters. I do not require seeing first hand when cold is creating a likeness of a lunar surface.