Newbie questions

OSBMXER

In 2019 we purchased a large c1918 home with hot water system with newer twin Burnham boilers. For the most part everything works fine, but I purchased "Classic Hydronics" book to learn more hoping to fine-tune it. Great book! I'm not an HVAC guy, but I am a machinist by-trade so I have solid mechanical aptitude. Based on the book, I can see a number of issues with our system. So I'd like to step all the way back to the first step to do a heat loss calculation to determine the actual btu load on this big house. We don't have a lot of big houses like this in my area, so relying on local contractors who rarely work on these type of systems is not realistic. Honestly, I'm more confident in my own capabilities for numbers crunching, especially if they get more detailed. So here's my questions:

1. Can anyone recommend an online heat calculator that allows me to enter my own partial-value numbers? (example: we have a mix of single-pane, storm, and insulated windows, so I calculated my windows HM to be 47.9). I was on the USBoilers.net calculator, and they only have selectable variables from pull-down menus (67, 41, 34, 30). I will need to do the same for ceiling insulation, since one section of the house has only 3" cellulose, and the other has R43 (R38 batt + R5 vintage 1.5" cork)
2. When calculating the building's height, do we use the interior wall height (8.5' for mine) or the exterior height that includes each level's floor trusses (10' for mine)? That factor alone throws the calc off by a lot. On a 2-story, that would be 8.5' x 2 or 10' x 2.
3. The 3 car garage is heated. Do we count that in the calc because it's heated, or leave it out because temp is not relevant there and heat rises to help the 2nd floor living space above? If counted, do we factor 3x overhead door sizes x single-pane efficiency? (another big number that could throw-off the calculation)
4. How do I calculate for a 2-story? The USBoilers calculator just asks for a square footage, but obviously a 40x50 2-story is entirely different than a 4,000 sq ft 1-story since heat rises and can be "re-used"?
5. I'm in Wisconsin. Is a 60 degree temperature difference factor correct for this region? Is the 60 degrees calculated based on "typical cold" winter days or "worst cold" days? Typical cold days would be about 10 degrees, but worst cold days would be -10 degrees which is 20 degrees different.

Thanks!

Ironman

Slant/Fin has a free app that you can download. A lot of your questions should be answered in the instructions.

Try it and check back here when you need more answers.

EdTheHeaterMan

The free online calculators do not have all the capabilities you are asking for. Many here recommend SlantFin's calculator. It has changed since I last used it, 20 years ago, so I can't tell you much about it.

To get as precise as you want, you need a professional program, and they cost $$$ (We don't talk prices here) If you are friendly with a supply house company that sells heating and air conditioning equipment, they have access to such programs. Maybe you could work with them on the project.

As far as using inside dimensions v. outside dimensions I have always used outside dimensions for whole-house calculations. It is easier to use a 100Ft tape around the perimeter then measuring all the rooms and adding them up. Same for the vertical measurement.

In a room by room calculation, you can change the window and door, ceiling, and wall U value factors as each component requires.

Of course you already probably know you only calculate the outside walls and ceilings for the load calc. interior walls and first floor ceilings with heated rooms above don't count.

For the garage doors, how often are they opened while heating is on in there? Are the doors insulated? How much glass, if any? Each of those can be entered individually for that room.

After it is all said and done, it is still only an educated guess at the size requirement. Actual usage is the best measure.

If your boiler cyclas off for more than 10 or 15% of the time during the coldest nights (That is called design temperature) then your heater is oversized.

If it is off for 50% of the time, during design conditions, then the heater is double the size you need.

Since you have an operating system and you can measure this stuff this winter during the ultra-cold. By using an electric clock attached to a relay that is connected to the Gas Valve or Oil Burner Fuel Valve, you can see how much time the fuel valve is open and compare it to a second identical clock that is operating full time. do this from 11 PM to 5 AM on the coldest winter night. This is the coldest time and usually, everyone is sleeping not opening doors, and using hot water (that only matters if your boiler makes hot water)

I hope this helps a little

hot_rod

This is my go-to program, 99 bucks, a trial version at www.hydronicpros.com
Or buy the design package with the HDS.

This software allows you to build customized walls, windows, floors, etc.
I don't know of any freebies that give you this much flexability?

EBEBRATT-Ed

Indoor temp for heating 70 degrees is usually used. Don't know where your located but Green Bay and Milwaukee are both -15 design temp

As far as the garage goes I would use 50 degrees. Your outside winter design temp is not the coldest temp you ever see, that usually only happens a few hours a year. I would think a 60 degree TD would not be enough. In Ma we usually use 0 outdoor design, VT is -10 in most places.

I would use the indoor dimensions for walls and ceilings or up to the level of the insulation in the ceiling or attic.

The Slant Fin program works well, not really detailed but detailed enough to be accurate.

You could do each room like it was a house in itself and then add up the totals, for instance lets say you have a 12' x12' room half the room has 6" of ceiling insulation and the other half has no insulation in the ceiling. Figure this room as two separate rooms. Obviously the "invisible wall between the rooms has no heat loss either way.

Heat loss estimates on an existing house when you don't know the complete construction (no xray vision) always have some guestimating and assumptions. Just use good judgement and it will come out fine. As far as your windows go if you do a room by room calculation you can vary your HTM as you do each room so it balances out

As far as the second floor goes the portion of the floors over heated areas has 0 heat loss. Likewise for the first ceilings under heated areas

EdTheHeaterMan

Yea... and what @hot_rod and @EBEBRATT-Ed said. Bob Rohr had been doing this longer than me.

nicholas bonham-carter

You may find, after you have calculated the heat loss, that you can stage-fire the boilers, so that only one is used in the milder winter months. As the temperature plunges, then the second boiler would be called on by a two stage thermostat.--NBC