AC done question about heatloss calc

TheKeymaster

Our AC is toast. It's 22 years old and needs charged. It's not worth putting the money into it and that's without even know where the leak is and the cost of fixing that. It's a new AC for us which we knew was coming eventually as we just bought the house this past January. The old unit was 4 ton. Some info. It's a super mid century modern architect designed home built in 1959 designed by one of the original students at Frank Lloyd Wrights school in NM. It has lots of windows. It's two floors, main floor is all above ground bottom floor is walk out on 2 sides. We have 2 forced air furnaces one for each floor but only the top floor has AC. The bottom floor stays 73 at most even when it's 93 outside and that's without the AC on the first floor even on and no windows open down there. It's all finished down there with a gameroom and 3 bedrooms plus a couple other rooms. So it's ok down there without AC. Basically the house floors are the same minus the kitchen upstairs is just a basement furnace kind of room downstairs. It's like 2 ranches stacked. Yes I know I will do heat loss to figure out the correct size of AC to use. My question is this. See 2 pictures. Two and a half sides of the house have windows like shown in the pictures. Almost floor to ceiling. So I know that will affect it a ton. Heating is actually really really cheap for the size which is surprising but the house is built to be efficient I guess. Each floor is 2200 sqft. Now my issue with what size AC to use is the second picture. The stairs going down are just open with a glass railing, but the furnace down there doesn't have AC on it. That's the only picture I had so you can't see the actual steps, but they go down from about where I'm standing to the 5 panel glass door. How do I figure out how much of my cool air will just flow down the steps? How much bigger of an AC will I need to over come this? I don't need the cooling down there so the little cool air that flows down the steps will be plenty down there to be comfortable. Also what do I look for in a good AC unit? I can research things but what is a starting point of things I should be looking for. Furnaces are old too so AC needs to be something that will be ok when we put new furnaces in at some point. Hopefully 5 years.

We were going to buy a house built in 1910 with hot water heat. I was all over these boards reading about that for weeks, so I understand I little about how to figure out the calculations. That fell through and we found this amazing house, but now I need to figure out the AC which I haven't read much of anything about. My background is carpenters union and now I do all the drawings for an architecture firm, so I'm a little bit above a diyer. haha I just don't know much about HVAC. I've learned a ton reading here but my wife is 6 months preggo so I don't really have weeks to do the research. Need to get this sucker figured out and someone to install it so my wife doesn't kill me in an overheated pregnant rage! This is why I posted the question to get a jump on what I should be looking for or at.

TheKeymaster

Not that it probably matters but I found a pic looking up the steps. There really is no way to add a door or close it off. Air is just going to flow down. As far as the heat goes I didn't even turn the furnace on downstairs this winter besides when I was doing some work down there and I don't think it got below 63 down there with upstairs set to 69. House is just really set up well. Basement furnace is a down draft and all the ducts down there are in the concrete. All in perfect shape too with no rust. Architect definitely was on site during the build because it is done right.

Edit: Forgot to say I'm in Pittsburgh Pa. We get more cold than hot but humidity is a killer here when it is summer.

STEVEusaPA

All the cool air that isn't captured by the return ducts will fall down the steps. Warm air rises, cool air sinks.
You size it like all the others, heat loss/heat gain, factor in the existing duct work, etc.
Have the contractor do that, and a TESP test.

TheKeymaster

I just thought that since the basement didn't have AC that the stairwell would almost be like leaving a door open 24/7. Nothing I have read about the calculations had anything about a situation like that. It's totally possible that since the basement stays very cool without the AC even on upstairs that even with the AC on upstairs the temp on the 2 floors will even out and the cool air won't flow down the steps as much because it might already be that cool down there.

I'm meeting with a contractor today, so we will see how thorough he is going to be. I'm hoping he doesn't walk in, look around for 30 seconds and say yup 4 tons is fine. That will just waste my time.

I do have another question, but it probably will get answered by the contractor today. The AC was 22 years old and so is the furnace. The furnace is working fine. Would it save me money to just replace that now too as it can't last forever? I'm just making these numbers up but let's say the AC is going to cost 3k now. A furnace say 5 years from now would cost 3k to install. If I did it all at once now would I save any money? Like would it usually cost less like 5k total instead of the 6k total doing them separate? Or should I just ride the furnace until it's dead. We have the other furnace on the bottom floor that I barely ever turn on that I could run if the top floor one died. It wouldn't be an emergency if it went out during a really cold spell to get it fixed immediately as obviously heat rises. The house has a ton of thermal mass so I could probably heat the whole house with the bottom floor furnace if I had too for an extended period. The house is double brick with about half the interior walls being double brick also. 80% of the floors are tile. There are 2 giant brick fireplaces in the middle of the floor plan too like 15 feet wide and 5 feet deep. Once I got it up to temp if I could it would hold it pretty well. That's probably why our heat bill in the winter is a joke. It's actually 10 dollars less than the house we moved from and this house is 2.5 times bigger. I actually made the gas company check it 3 times because I thought it had to be a mistake and didn't want to get a surprise bill in the thousands once they caught the mistake. Nope it really was that cheap.

GBart

Do it all at once, one labor charge plus new systems should be a matched set, all one brand, mis matched components don't always work well.

DanInNaperville

If you have a center chimney house with exposed brick (and that's how our house is) do NOT get a condensing boiler. It would be utterly pointless and add to your costs with zero benefit.
During the winter with the heat on, I've used a remote thermometer (those things you get for 20 bucks at harbor freight) to monitor the fireplace/brick chimney temps. I've since picked up a FLIR and am looking forward to what I see this winter. When the boiler's running, brick temps range from 10 degrees above room ambient near the floor (and closest to where the boiler flue enters the brick chimney) to room ambient near the ceiling.
I'm getting mod con boiler efficiency without the cost and maintenance problems of a mod con boiler and you could too.
If I were to pipe in outside combustion air and add a flue damper, I'd be getting 95% to 98% from my old burnham that's rated around 78%.
The living room is on one side of the chimney with the boiler's flue and a bedroom hallway (exposed brick as well) is on the other side. It also gets warm and acts as a panel radiator.
I am going to do some exploration of the bottom of that flue and keep an eye on what I expect is a clay liner - that condensed water has got to be going somewhere....
This past winter was my first in the house and at first I couldn't understand why the heating bills were so low.

TheKeymaster

It's a forced air furnace not a boiler. I read a lot about mod con boiler when we were initially going to buy a house that had radiators. I thought pretty much all furnaces now were condensing. Am I wrong? Those are the kinds of questions I'm looking to find out.

HVAC contractor came out today. He's going to work out some numbers for me. I have 2 other guys coming out next week. I'll have some numbers to compare. All 3 guys that I've talked to said that it's really hard to do manual J calculations on a house like we have. (not sure if this is true, but their logic seems to make sense) The crazy amount of windows, all the brick. Not to mention it used to be a flat roof and when the original owners put on the first new roof they put on trusses and added a slight slop so they could use rolled asphalt. It's got a few different slopes just guessing but ranging from .5/12 to 2/12. There's no access to the area in between, so I have no idea what's in there. With the low slope and the size of the house I doubt I could get more than my head up there and only in the center. My guess is that the original flat roof had some insulation and when they added the new trusses and deck they added more. That with the airspace seems to be making up for the shear number of windows on how much heating is costing me as it is very cheap.

Ironman

Any a/c that is higher efficiency will require a matched indoor coil and a furnace with an ECM to get the rated efficiency (the blower factors in the SEER rating). Do the entire system now if you can afford it.

I've done manual J calcs for almost 40 years and I have no idea why those contractors would make that statement other than they are either incompetent or lazy - or both.

@DanInNaperville
Welcome to HeatinHelp.

I would like to know the scientific reasoning for your statement that a mod/con is useless if the house has a center chimney. It will have to go beyond the fact that the chimney radiates SOME of the heat from the flues gases back into the living area.

DanInNaperville

Hi Bob,
Not any center chimney but it looked like the case in his house and certainly is the case in my own. The reason a mod con doesn't make sense in this installation is that, effectively, it already has one (that's cheap to buy and run and stays efficient). The hallway wall is only 8 feet high but the living room is vaulted to 17 feet, and the brick in which the flue runs has roughly 20 feet from where it enters the masonry till it gets to the ceiling. That's more than enough to condense the vapor and capture the heat (then radiate it back into the house - just like a condensing boiler does).
Last winter we had extended periods of -10 and lower here and I saw only a little steam condensing above the chimney in a plume - it was about what I saw from some neighbor homes with about a 3rd of the heat (cold?) load. My house is big ranch with a 440 sq ft sun room, heated basement and heated garage. (most local homes are 2 story or split level and don't have silly sized sunrooms or heat the garages). A two story has less surface area per sq ft and is a lot more efficient a design for reducing heat loss than a ranch.
My old 266K BTU input atmospheric vented boiler should have been putting out a (relatively) huge plume but instead it was smaller than many neighbors. The house was warm and the gas was burning so that big long run through the tile flue must have been condensing out most of the latent heat.
It's extremely efficient but I need to check on what (if anything) the condensate has done to the masonry - maybe I need to dump some limestone down the chimney!

Ironman

Well, I was gonna ask if you thought condensation in a masonry chimney was a good thing?

Jamie Hall

@DanInNaperville has a real point about masonry centre chimneys. So does @Ironman .

To Bob's comment, condensation really isn't a good thing as a general rule, but a properly made and maintained, lined chimney can take it. Note. Properly made in the first place, and maintained -- which means you get a competent chimney sweep out there at least once a year and really look at the thing. The concern, of course, is the mortar between the tiles lining the chimney (if it isn't lined, all bets are off), as the condensation may attack it. May not, too.

To Dan's comment -- the effect is quite real. It is also hard to quantify. However, any heat radiated inside the conditioned envelope -- such as a an interior chimney is not a loss, and should properly be counted in in figuring the overall efficiency of the system. As an extreme example, one often hears that a fireplace is a horrible waster of heat, and some are. But a properly designed fireplace (there aren't that many) in a really heavily built masonry chimney can do a very good job of heating the space it's in -- nearly as good as the best wood stoves. There's one in the main place I care for which burns cordwood (4 foot logs), but is only 2 feet front to back (yeah, have to be careful about sparks!) but is in a chimney which is 4 feet thick and 16 feet wide -- and heats the room it's in (30 by 15, 10 foot ceiling) and the room above it (ditto) and the rooms behind it very nicely indeed -- it will happily hold a 60 degree inside/outside temperature differential with a very nice civilized fire.

TheKeymaster

So my first estimate is in. Is it me or is this quote insanely vague. It might as well have 3 prices listed A,B,C with no other info. It doesn't list the full model numbers so I can't tell if they are putting in a 60k btu furnace or a 100k. For the Aprilaire units it only lists the brand and not what model. Huh? I guess I should just assume the cheapest thing Aprilaire makes then is what they are quoting.

I was pretty sure this guy wasn't getting the job right after he left anyway. He didn't measure anything besides the duct coming out of the furnace, he didn't even ask me how many square feet the house was let alone measure for himself, he didn't ask if the furnace we had seemed to work well for it's size or whatever and he didn't even walk through or around the outside of the house besides one room that I showed him that the lines went through the ceiling going to the AC outside. You couldn't even do the dreaded rule of thumb with the square feet of my house because it's Frank Lloyd Wright style being the common areas have high ceilings and all the other rooms have low ceiling that you don't spend time in like bedrooms. I'm only 5'9" and in our 3 bedrooms on the main floor if I have shoes on I can put my hand flat on the ceiling standing flat footed. That's a ton of volume difference than typical room height. I mean, I have a pretty cool and unique house even if he didn't measure anything, you'd think he would want to take a peek to just see what the windows looked like in each room as they are far from standard sizes. There is so much that he didn't see that he probably needed to see. Like the master bedroom has a full wall of floor to ceiling window with double full glass doors in it. Our hall bathroom has double glass doors in it going to the outside (not sure why, probably if we wanted to add a hot tub outside those doors would be a good spot). Hopefully my next 2 quotes will be better. Coming today and Thursday.

DanInNaperville

Ironman said:

Well, I was gonna ask if you thought condensation in a masonry chimney was a good thing?

In my previous house, I had to replace the top 10 feet of the masonry chimney (not cheap!) because condensation from the natural gas forced air furnace dissolved the mortar. That cost was about twice what a stainless steel liner would have cost.
OTOH, my furnace was as good as new after 20 years - maybe if an SS flue liner had sent that mixed acid condensate back down to the heat exchanger, it would have rotted it out and made me buy multiple furnaces in that same time period. I sure don't know...
Hence my determination to "check on what (if anything) the condensate has done to the masonry." Does anybody know if someone makes limestone flue liners? A google search suggests it would have to be cast in place and might do too good a job of insulating the brickwork and sending that heat up the chimney instead of into the house.

TheKeymaster

2nd quote was thorough. Probably end up using that guy but have one more guy(4th)coming.

3rd guy came today. What a clown! He wasted an hour of my life. Asked me how many square feet the floor was. I started to say about 2000 to 2100 and he interrupted and said as long as it's with 500 it's close enough. WHAT??? He didn't measure anything or even write anything down. I had to drag him up to the main floor to see the space that the furnace would heat and cool. He kept saying he didn't really need to see it, he's got the idea and he saw it has lots of windows. He then asked me what size furnace and AC unit I wanted. Umm that is why I want a quote and you to do some math.

This one is the kicker though. I'm noticing lots of condensation from a non insulated slab that is probably much more noticeable now since we have no AC running on the floor above. I'm guessing the AC upstairs took the edge off the condensation enough so I didn't notice it. I asked him about adding a whole house dehumidifier to our lower level furnace and he said you mean an AC unit? I said no it's 92 outside right now and it's 71 down here. AC isn't going to dehumidify jack unless I want to cool it to 60 down here because it won't run long enough. He said like a single room unit you can get at like Lowes? I again said no a whole house dehumidifier. I can't dehumidify 6 rooms and a bathroom with a single room unit unless I get a few of them and spend 400 on electric for them a month. He said he didn't know that was even a thing and he would need to look into it.

I really wanted to tell him don't even bother writing me up a quote, but then I thought, he wasted my time so he can waste his own time writing a quote that I won't even look at.

What an annoying time I'm having finding someone competent. I'm most likely going to use the 2nd guy as he was the only one that was any good. What's the point of getting multiple quotes if only 1 is worth a damn. I wanted to get 3 good quotes but now I'd be happy with 2 that weren't crap so I can at least compare those 2. I feel better after my rant and I thought you guys would get a kick out of how bad the guy was today. ugh such a waste of time!

NY_Rob

^ a lot of hacks out there....

Our neighbor at work had a single head 18KBTU mini-split installed last week by a "professional" HVAC company with a nice work van with color graphics and logo on it and all.

I popped in to check their work as I just self installed my own 4-head 36K BTU mini-split and wanted to compare their install to mine. Well, believe it or not... the "professional" HVAC company installed a MrCool DIY unit that comes with the sealed/pre-pressureized linesets! The lineset runs were a mess, none were straight, they were twisted over each other at one point and they didn't use lineset covers... just the ugly plastic wrap that MrCool uses. They ran the condensate drain line into the nearest sink basin... not into the drain system... into the sink bowl itself. The install was a complete mess. I would give it a 2 out of 10.

I asked the owner about servicing the filter because they mounted the unit very close to the ceiling and I didn't see how she would be able to remove it... she said she didn't even know it had a filter or that it needed servicing. She told me they handed her the remote and the owners manual and they took off.

The whole install took about 1.5hrs, they started at 4:30 and were done by 6pm. I guess that's possible when you don't have to cut/flare lines, pressure test for 24hrs or even overnight and you don't triple evac, don't check subcooling, skip installing lineset covers, etc...

TheKeymaster

Had 5 quotes done. 3 were totally worthless. 2 were good. We are going with the last one we just got this morning. It's not the cheapest in fact it was 1 down from the highest but the guy was the best. He reiterated a lot of the things I've read on these forums before I could even bring them up. The other good quote I had to bring things up and I'm not sure if he was actually going to do those things or he was just giving me lip service so I stopped questioning things. The guy we went with had an answer to every question I asked and I know he wasn't just blowing smoke because I asked lots of questions that I already knew the answer too to see what he said.

In the end we are going with an American Standard 100k variable and a 4 ton AC. Our previous 4 ton AC was sized correctly because of all the solar gain. The furnace at 150k was way oversized. He said Lennox 90k would have worked too but AS doesn't make a 90k so 100k it is. Adding an aprilaire cleaner to both furnaces while they are there. Plus adding a dehumidifier to the downstairs furnace to quell the slab condensation we are getting. Spending a little extra for a 120 pint honeywell DR as can't really oversize that and it's going to get a little more taxed when we don't have the AC on upstairs and have windows open up there. Hopefully they can get this all installed before it goes back up to 90+ or my pregnant wife puts a pillow over my head while I'm sleeping.

The only reason I went with American Standard over the Lennox was because he said they are a little easier to work on occasionally for some parts like heat exchanger. Is that correct? That was something I can't really look up for myself. It's was only a couple hundred more so figured if it wasn't true I'm not out much.

TheKeymaster

As I was typing that last reply, the hack I was talking about in the post above Robs emailed me his quote. It's about 70% the price of the guy we are using. I'm still not going to use him. He was the one who said he wouldn't change out the r22 old lines for new for the new refrigerant. For the record my old lines are buried for about 15' because the condenser is so far away from the house. (I'm moving it for new one). They aren't in conduit or anything not even the wires. They come out of the ground 4 feet from the condenser and are just exposed there to be hit with a mower or deer to trample. He said they are pretty much the same and it would be fine. LOL Plus he quoted some brand that I never even heard of even after reading these forums for many many hours in the last 2 weeks trying to get informed. I'm sure by going with a higher quote, I'll be dodging a bullet not using this cheap quote by this hack.

pecmsg

Burred line sets have there own issues.

15' is a long way, may want to consider a pump down system to prevent slugging liquid.