Calculating heat loss

[tkarvelis]

I am in the process of building my garage. The building is 48x32 with 16’ ceilings. The walls will have r20 spray foam (3 inches of closed cell). The ceiling will be blown in fiberglass. The walls have three 6x2 windows, one 32” fiberglass man door and two 9x19 garage doors that are insulated.

The concrete is 5 to 6 inches with 1500’ of pex

I plan to use propane to heat

Is there a way to calculate how many btus I will burn per day?

I live in south west pa

I plan to heat the building from November until March or April with a temperature of 55 degrees

I planned on using a modulating boiler which has a maximum rated btu of 120,000 BTUs

Propane is about $3.00 per gallon

 

[tkarvelis]

I forgot to add that the concrete had 2” of xps foam under and around the perimeter

 

[danski0224]

I hate plugging it because the software has not been updated in years, but HVAC-Calc will sell a single use license for $50, last I looked.

There is a demo on the website.

The software will not work on higher resolution monitors unless the settings are changed, and it has been like this for well over 10 years.

If Google is working for you, then try that. There are plenty of options. Might want to try more than one to double check the results.

There are companies/people that will do it for a fee. But typically, no one posting here wants to pay.

 

[Modoc]

You could always just use the official WAG rule of thumb of approximately of 25 btu’s x sqf… ball park I emphasize ball park.

 

[fitter30]

1500' 1/2" pex is 32 btu per foot X 1500= 48k btu's

 

[ericm]

I have used loadcalc.net to run Manual J and S (which sizes equipment based on the manual J output). I was able to get pretty close to the Manual J/S calcs the HVAC company did for my house. Some of the difference may have been due to my estimations of the house shape. The house had a lot of bits sticking out. A plain rectangular shop is a lot easier. So far the units I spec'd for the shop based on my Manual J/S from loadcalc have very easily kept up. But it's only been a few months and it's not been super cold (for here) yet.

One thing that the Manual J process showed me is that I need much more heating than cooling. Considering that it gets above 100 pretty often in the summer and goes past 110 at times, that surprised me.

Be careful to put the appropriate numbers into any field in loadcalc.net that looks like it needs them. If you miss some the results can be off. When I did that the numbers came out low. The one difficulty I had with my shop's calcs and loadcalc was them not having insulated garage doors as an option. I used "solid core with storm" as the closest to the insulated panel doors I got. I have three 12x12s on the heated part of the shop so it matters.

 

[kngelv]

Your spray foaming the walls but the ceiling is blown fiberglass?

James

 

[Modoc]

1500' 1/2" pex is 32 btu per foot X 1500= 48k btu's

Bingo or close

 

[lovetap]

1/2" pex? Spacing? How much insulation in the slab? Whats the average ambient temps around there?

I'm in a colder environment here, but I used almost 1000' of 1/2" in a 16x40' garage.

 

[kj_mustang]

I have a similar building. 32 x 54 x 16. 2" CC spray foam on walls and eaves, roof has 2" CC and then another 6" of open cell, insulated garage doors and man door, with a few windows. I have 6 loops in the floor so close to 1800'. Loop calc estimated that I run about 35,000 BTUs. I can hold it at 58 degrees quite easily over the winter. I can't give you any propane usage numbers because my house and the detached garage all pull from the same tank. I can say I don't think I use very much given the number of devices burning propane.