Nathan Davis
Member
I need a sanity check for my heating figures.
In the attached spreadsheet, you will notice the EDR and calculations on the Btu output and water volume for each of my hot water radiators. The Btu output and water volume look high to me. For instance, the “Entry” radiator has an EDR of 6.3 (it is 23” high and 5 tubes), and includes a total of 26 sections. I’m showing this will output 27846 Btu. Wow, that seems like a lot for a single radiator!
Moreover, if you look at the second page of the attachment, you will see that this same radiator should hold 25 gal of water. Again, that seems like a lot of water for one radiator. Are these calculations really right, or am I figuring something wrong?
If these calculations are right, then my existing system (see second page of attachment) holds 575 gallons. That seems incredible. It’s more than I can believe unless someone else can verify that I’m figuring things correctly.
I have four questions:
1. Since the capacity of my radiators seem over-sized for the Btu needed to heat the house, I notice that they never get fully hot before the house warms sufficiently to turn the thermostat off. Because there is so much water in the existing system, I need to set the thermostat to turn the boiler on at least 75 minutes before we get up in the morning. That is, there is so much water in the system that it still takes our 200K Btu boiler about 75 to 90 minutes to heat up all the water in the system. And even then, when I touch a radiator, it almost never seems too hot to touch. If my replacement boiler is 50% smaller than my existing boiler, then I wonder if it will take about twice as long to heat up all the water (2.5 hours)? Regardless, if I’m saving money due to a higher efficiency, that’s OK.
2. With the existing boiler, we usually turn the thermostat down about 3 degrees at night and while we are gone to work during the day. Since the replacement boiler will have a 10:1 turn-down ratio, I’m wondering if we will find it just as economical to keep the thermostat at full temperature, instead of turning it down 3 degrees?
3. The 100K Btu replacement boiler will still need to heat 550 gallons of water in the entire system. With such a large volume of water to heat, I wonder if I should consider adding a 50 gallon hot water storage tank for preheated water, constantly held at 180 degrees? Conceivably, I could even add a solar panel to keep that water preheated.
4. I’ve also noticed that the oxygen barrier coating for pex seems to rub off fairly easily. So I expect that some will get rubbed off as I install new lines. Is there any spray that I can use to reapply the barrier where rubbed off?