How much work is the heat load calc

I think 10-12 tons is probably going to be overkill if you intend to improve the building, but how would I know?

Seriously YOU need to take the measurements and run the math and come up with the total heat load number. I won't just keep taking WAGs at the size of windows & walls etc, since it's something that you should be able to measure up in under an hour. I've shown you the methodology- running an I=B=R type load calculation is 5th grade arithmetic, no rocket science required. All you need is the U-factors of the different stackups and the gross area, then it's:

U-factor x square feet x temperature difference= BTU/hr

Typical ducted air source heat pumps can deliver over 10,000 BTU/hr per ton @ +5F outdoor temps, but ductless systems will usually deliver over 13,000 BTU/hr per ton at +5F, but you still need to read the specs with the extended temperature capacity tables/charts to estimate the system capacity at any given temperature.

Those hollow concrete blocks are neither bricks nor cinder-blocks, but rather "concrete masonry units", (CMU). True cinder blocks using coal-cinder-aggregate/portland cement concrete haven't been commonly used in the US since the 1940s. Anything newer is usually a stone-aggregate concrete with better structural characteristics. The U-factor for 8" CMU wall with nothing but paint (no siding, no wallboard) is about 0.9 BTU/hr per degree-F per square foot. Any guess at a wall height is just a guess, but you can measure it subtract out the window & door area, and come up with a number.

Adding 2" of rigid EPS held in place by an overlay of 1x furring 24" o.c. through-screwed to the CMU onto which you hung half-inch wallboard would lower the U-factor of the wall to about U0.09, reducing wall losses by 90%, taking up about an inch less interior depth than a 2x4 studwall insulated with batts that performs about the same.

Aluminum-framed single-pane double hungs are about 1.1 BTU/hr per degree-F per square foot.(Not quite as good as wood-sashed windows due to the higher conductivity of the aluminum compared to wood.) You have 17 windows at about 7.8 square feet, for ~133 total square feet, so the window losses are about 1.1 x 133 x 70F= 1024 BTU/hr

Adding low-E storms would get you to about U0.37, reducing the window losses to 350 BTU/hr (about the heat emittance of one live human).

The roof is about U0.4, as previously assumed.

For the basement, run the numbers on only the portion of the wall that's above grade down to about a foot below grade.

I apologize, yes you've been more than good explaining and I can do the math. I thought you had some software or something that would spit out a good approximation. But I can sit down one evening at the church and see what I come up with.

This is from the last contractor... Looks like about $5k per unit so it would sure be great and more in line with our budget if we could get away with 3 instead of 4 units. That fifth one he mentions is way out of the question for now. lol

Attached is the proposal for the ductless system. I did the quick heat load calculation and the load comes back just under 10 tons. The four units will handle 10 ton of cooling. The loads were ran to maintain 75 degrees inside when it’s 94 degrees outdoors. I did give you an option to add a fifth unit. This will give some buffer room for unknown building materials used in the construction and for hotter days.

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The 30RLX (or any of the RLX series) is a 2.5 tonner, and not really designed for your outdoor heating design temps. You'd have to request the extended temperature capacity charts, but they may not even be rated below +15F or so. The xxRLS2s have a rating at +5F, but IIRC the biggest of those is a 1.25 tonner.

You're probably better off with Mitsubishi's H2i lineup, which will still hit ~85% of their full rated output at -13F, and fully automatically defrost, etc., and come as small as 3-tons to a package.

Dana said:

The 30RLX (or any of the RLX series) is a 2.5 tonner, and not really designed for your outdoor heating design temps. You'd have to request the extended temperature capacity charts, but they may not even be rated below +15F or so. The xxRLS2s have a rating at +5F, but IIRC the biggest of those is a 1.25 tonner.

You're probably better off with Mitsubishi's H2i lineup, which will still hit ~85% of their full rated output at -13F, and fully automatically defrost, etc., and come as small as 3-tons to a package.

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The problem i have is finding someone who sells and installs the Mitsubishi's in my area. The one guy we thought represented Mitsubishi quoted two traditional 80% furnaces with AC on the flat roof at the back of the church. However, I've been told many times by many contractors that our single cold air return is a huge obstacle to traditional AC. The Mitsubishi guy says it isn't, we just need more tonnage.

That's why I wished manufacturers still sold and serviced their products directly. I went to the Mitsubishi website and requested to be contacted, and this was the guy who contacted me... Tried to sell me something else and really sounded negative about what mini-splits could do and even suggested just the cooling and no heat.

Find another Mitsubishi installer- it sounds like that guy didn't have enough experience to be comfortable specifying the bigger units (or even the smaller ones.) It may take a few tries before you find the right contractor, but this isn't rocket science, especially if YOU do the room-by-room load estimates to help narrow it down.

Going with the xxRLX Fujitsu series would be a mistake IMHO- take that guy off the list too.

Unless you are desperate and need immediate replacement of the mechanicals it's worth taking your time to find the right contractor.

Dana said:

Find another Mitsubishi installer- it sounds like that guy didn't have enough experience to be comfortable specifying the bigger units (or even the smaller ones.) It may take a few tries before you find the right contractor, but this isn't rocket science, especially if YOU do the room-by-room load estimates to help narrow it down.

Going with the xxRLX Fujitsu series would be a mistake IMHO- take that guy off the list too.

Unless you are desperate and need immediate replacement of the mechanicals it's worth taking your time to find the right contractor.

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I learned not to rush in life, patience allows you to do it once and get it right.

Thinking about the Mitsubishi being 3 tons, we could install 3 of those which is 9 tons and see how it goes. Then we can always add another if needed or we can start weatherizing the building to see how that goes. The cooling should be fine this summer it's the winter that may not prove adequate but we still have the old furnace to fall back on so???

I've been reading where people get better deals buying the units themselves then paying someone just to do the install. Somewhere I read where some paid $100 for an install, I expect to pay more than that but that's promising and would come to a lot less than the $5K per unit...

I first need to do the calcs but I have two funerals this week plus 1 hour bible study and two sermons to prepare for Sunday. I generally spend about 5 hours for every hour of bible study and about 20 hours per sermon so including the funerals, this will be one busy week.Hopefully I can figure out the calcs next week lol...

EDIT TO ADD... After rereading, the H2i is one large unit that takes multiple heads. I like this even better, cuz we can not only heat/cool the sanctuary but we can also add units to other parts of the building and perhaps keep the boiler off until really needed or use it to augment the boiler in the rear part of the building but can definitely add cooling to the rear and perhaps downstairs (though most say if we cool the upstairs the downstairs will be cool by default).

How do i find the price of an 8 or 12 ton H2i? I'm not finding anything on google?

I woudn't trust the competence of ANYONE who would install a mini-split for $100, and unless installed by a competent contractor (preferably with manufacturer's certifications to know that they at least slept through the training course ) it would not likely be covered by any warranty.

There are H2i multi-splits of many sizes- some can support something like a dozen heads/cassettes. There can be capacity limitations if the refrigerant lines have to be run too far a distance from the compressor, but if the installer was actually AWAKE during the course they'd be able to avoid that level of stupid-attack.