Adding A/C to my old Victorian house

SHS111

Various options have been proposed, one is suggesting that we replace the current warm air furnace with one that will accommodate a/c input as well, using the current heating vents. The primary heating in the house is steam, the warm air vents are in some rooms, not all (my guess is that they're holdovers from the old coal system). These vents are on the floor or lower in the wall, not where I'd ideally want a/c vents (warm air rises, cool air falls), and we'd have to cut in and add some more. Thoughts?

Paul S_3

where are you located....most heating only systems cannot have ac instalked with the current ductwork

HVACNUT

1- Does the steam system adequately heat the whole house?
2- Is the furnace in use? Steam coil?

If the answer to 1 is yes, and the answer to 2 is no, look into a Unico or SpacePak system. They're designed to accommodate ducts in areas of difficult access.
And have the old furnace and ductwork removed. But post some pics of the furnace first.

Kybeans403

Where are you located? Unico has a contractor finder page that can help you find a qualified installer, unless your in Fairfield County, CT or Westchester County, NY, where I'd be happy to help.

Not a good idea to try and hack in a coil on top of a furnace with ducts that were designed to only carry warm air. You can add supply vents, but returns on upper floors are essential along with an ecm blower on furnace to have any hope of cooling upper floors.....don't do that. Excessive new duct work, soffitt work after the fact and a system that isn't guaranteed to work will end up wasting your money.

Small duct high velocity systems were designed to cool houses specifically with old steam or hot water systems. A main trunk line, usually 7 to 10 inches in diameter is installed in the attic and feeds for each room can be installed in the ceiling and fished down in closets or interior walls to reach the 1st floor. Minimal, if any plaster/sheetrock repairs are needed after job is done. If sized and installed properly, a single system cooling 2 floors can maintain temperature with less than 2 degrees difference between floors.

ratio

Perhaps mini splits would serve your needs. They are available in heat pump models (would be adequate during swing seasons, possibly into heating season) and cooling only models, with one or more indoor units per outdoor unit. They are available in wall tumor models that everyone is familiar with, but also in concealed ducted models and floor/wall mounted units similar to an enclosed radiator. They can be coordinated with your steam system (with lessened efficiency, as I've learned, for single-control; i.e. one thermostat for both systems), and will perform swimmingly so long as they're sized properly.

jumper

How many floors? In old homes you can put ducts in attic and at least cool the upstairs. Rest of house can depend on cold air falling through staircases. Generally a house with cool upstairs won't be too bad downstairs unless someone cooks up a storm.

Fred

I have steam heat in a 115 year old 5000 sq.ft. , 3 story + basement house. I kept the steam, would never give it up. Initially I put a forced air furnace and central air in a storage area on the third floor. I was able to duct the third floor with registers at the top of the walls. I managed to get ceiling ducts to each room on the second floor. As @jumper said, I depended on the air falling down an open staircase to the first floor. for the first four or five years. It was okay as long as the outside temps stayed in the low 80's or any cooking happened. I then put a second forced air furnace and central air in the basement, ducted to the first floor with floor registers. Should the steam fail, for any reason, I can heat the house with the forced air systems and the air in the summer is like dying and going to heaven.

SHS111

Thanks to all for the comments. I've explored different options fairly extensively and find myself returning to the idea of a Unico high velocity system. The proposal is extremely expensive, which I understand given the size of the house (would require 11 tons, three systems, total square footage 7200 for the three levels). I'm thinking about proceeding with "first floor only" as a starting point, because it would help break up the cost (could do 2nd and 3rd floors later) and also because I'm not wild about the loss of closet space that's going to happen for the 2nd and 3rd floor systems. Is it crazy to central a/c the first floor only? This would be a 5 ton system. The advantage is that the access is easy through the basement, and I don't mind the idea of having supply outlets on the floor.

Jamie Hall

The Unico is one of the best options for an historic house, as the ducting is relatively easy to route and small, and the outlets aren't intrusive (unlike almost any other option).

And no, it's not crazy to just do the first floor. Unless you are located well south evenings are usually cool enough so that with some open windows sleep is possible on all but the hottest days of the year-- and the fact that the upper floors gets hot in the daytime isn't really a deal breaker.

SHS111

Thanks Jamie. Exactly what I'd been thinking, and hoping to hear. Really appreciate your comment. And we're in the Boston area, so evenings generally do cool off. And personally I'm not a big fan of sleeping in an a/c room.

Tinman

5 tons of AC for the first floor with a conditioned space above? Which way is your home facing? Is there a lot of glass on the west and south sides?

ChrisJ

Stephen Minnich said:

5 tons of AC for the first floor with a conditioned space above? Which way is your home facing? Is there a lot of glass on the west and south sides?

Using my uninsulated, drafty house with all original, drafty windows with an indoor temp of 70F as a reference I come up with around 5800 for 11 tons in my area of NW NJ.

Either that, or someone didn't do a proper heat gain...…………

I'm thinking you're thinking what I'm thinking. Wow...….wouldn't that cause a feedback loop?

SHS111

Question of clarification: what do you mean by "conditioned space above?" And the windows face in each direction, most face east, south and west.

Tinman

Conditioned space above refers to the second floor which isn't being cooled, but has yet a 3rd floor on top of it. If I were doing the load calc., I would not consider it an unconditioned space necessarily.

Old Victorians are typically "loose", but also not enormous like many of the homes being built today.

My point being, I'd make sure the calc is accurate. Cold and clammy is uncomfortable.

SHS111

Thanks for the clarification. I calculated the approximate square footage of the first floor which is approx. 2400 sq. feet. Tall ceilings (10 ft.) too.

ratio

What everyone is getting at is that 5 tons of cooling is a spanking LOT. It's within possibilities that you do actually need that much, but it't is far enough from common that people are questioning it. 11 tons is just flabbergasting. I do all three floors of my 1920's not-too-tight house with 2½ tons.

Heat gain calculations are imperative for the proper sizing of cooling equipment. Too big is actually worse than too small. Can you share how you came up with 11 tons total & 5 tons first floor?

SHS111

I didn’t, the estimator did. Not sure how he came up with it. Although he is a sales guy, of course.

brandonf

The best way I see to do it is make sure the steam can handle the heating completely, and then get a Unico system for A/C.

JUGHNE

Just for comparison. I did our small movie theater with only 2100 sq feet, 14' ceilings. Fair heat gain with 30' of west facing display windows behind screen. Minimal wall insulation with 8" brick walls. Good attic insulation.
AC system is 3 units totaling 8 tons, (96,000 BTUH).
Two 2 tons thru floor diffusers.
One 4 ton unit feeding thru ceiling above seating area.
This will keep the building down to 68 degrees with out feeling "clammy--humid).
Half of that cooling load is the 65 or more people sitting side by side.
The other half is the building gain, projector bulb, concession stand heat gain etc.
In 8 years of operation I have not heard any complaints.
Most bring a sweater.

This is in central Nebraska, I used 95 for outside design temp.
We have fairly high humidity.
Just food for thought.

mikeg2015

I’m cooling an entire 3500sqft 1905 brick victorian with original windows with 5 tons total. Need about 1.5 downstairs, 2.5 upstairs. Install 3 tons up, 2 tons down. A very well insulated and installed 2 tons conventional system would have worked upstairs. I went wit ha UNICO that ended up being poorly installed. I have a full 3rd floor attic that I may insulate and partially finish some day. It’s partly vented now.

Something that the “professional” load calculations don’t consider is stack effect on taller homes. With air leaks, you get stack effect. Stack effect is hot air rising and cool air falling. In winter warm air rises and creates a negative pressure dwonstairs drawing in col dry outdoor air. Warm humid air indoor air rises and goes out any leaks (why air leaks in a unconditioned attic cause moisture issues and frost).

In summer, the process reverses. Wamr humid outdoor air leaks in upstairs as cool indoor air falls and going out downstairs leaks.

If you have Radon issue for example, they get worse in winter and better in summer. My levels stay under 4 in the basement and under 1 on the main floor, but drop but 1/3 in summer, and another 1/2 of that on a windy day.

So I only have a steam humidifier on the downstairs conventional heat pump system, and upstairs, I have a Unico thats really good at dehumidying. Heat pump allows my to zone the upstairs and downstairs in mild weather when the boiler would tend to short cycle, overheat the house.

So yeas, you can cool just to downstairs cool air falls and hangs low. I bet 3 tons would be adequate, would dehumidify very well and be comfortable at 75F. The warmer you can keep it, the less capacity you need and lower your bills are and more even the system is, more ductwork, most cost... so on. On very hot humid sunny day,s it may run continously for 20 hours, and you can’t use setbacks. But honestly setbacks don’t save much because on the hotest days you need an oversized system to use them, which is inherently less effecient, then you are deferring run time from a cooler time of day to a hotter time of day. Effeceincy drop the hotter it is outside. Only time you might set back is maybe from 3PM-8PM but a properly sized system might take 4-5 hours just to recover 1F.

Look at it this way. IF your driving on the highway and you stop at a rest area, you are moving 0MPH or that time. How much slower could you drive if it never stopped? Now lets say you were driving 64mph and you don’t want to go over the 65mph speed limit? It might take 3-4 hours to catch back up that time. Make sense?

With a smaller system in a larger space, youll be surporised at how few registers you need in each room and a central return near the unit will work just fine. I have 1 large 6”x14” grills (commercial return grill flows the most air, dampers should be installed at the plenum), and just ran 8” flex to each register. Easy-peasy. One duct for each room. Smaller rooms use a smaller grill. Add more air for south facing or west facing rooms, and less air for interior rooms, more for a kitchen unless you have a large range hood. If you have a large range hood, you need a 6 or 8” make up air intake with a damper linked to it.

Good location for a return Is a central foyer, or on a wall with a closet on the other side that you can install the duct. The central foyer does not need any registers. Don’t both conditoning small entry ways.

Professional load calculations often use too high of an air leakage rate, underestimate actual R value of uninsulated wall assemblies, don’t factor in thermal mass (the mass of walls and floorings that stores thermal energy). Old homes ride through outdoor temperature spikes.

ON a 1925 home I owned with stucco over hiplap with good storm windows and large air gaps in the walls, and spray foam under the roof deck, I cooled 3200sqft with just 3 tons total, but had 2 tons on each floor. Downstairs the humidty was usually under 40% RH even though it was a dewpoint of 75F+ outside. Heated it with about 60k BTU total too. Had 120k installed since 60k is the smallest furnace in some models of equipment.

SMALLER is BETTER.... just keep repeating that. LArger is better for the installer. They make a bigger sale and most ignorrant customers prefer oversized equipment because thye hit the button and it cool off fast, its what they are used to.

Fred

I have 5000 sq. ft. 2000 on first floor, with a 3 ton A/C, 2000 on second floor and 1000 finished space on third floor. Second and third floors are cooled with 5 ton A/C for a total of 8 tons. I keep the temp at 68. No problem with clammy/humid. House is 12" brick, all original single pane glass.

ChrisJ

11 tons in 2400sqft!

That's ridiculous even by my standards.

I'm running 3 tons in 1600sqft and many said I was nuts and should have gone with 2 tons. But, I keep my house 71-72 during the day and sometimes 68-69 at night.

I have 26 windows most of which are from the 1860s and very loose. My walls are empty with nothing other than clap board and aluminum siding on the outside. Attic is unvented and house is 2 floors.


If I had to guess without seeing anything, I'd bet 1.5 tons per floor, maybe 2 tons for the top, at the absolute most. Assuming each floor Is equally 800sqft.

So, 4.5-5 tons total. Tops.

ChrisJ

Fred said:

I have 5000 sq. ft. 2000 on first floor, with a 3 ton A/C, 2000 on second floor and 1000 finished space on third floor. Second and third floors are cooled with 5 ton A/C for a total of 8 tons. I keep the temp at 68. No problem with clammy/humid. House is 12" brick, all original single pane glass.

Many seem to forget if you maintain a lower than normal temperature, the system will have to be larger than normal, and yet will still dehumidify fine because it's always working harder than normal.

There's nothing nicer than walking into a 68 degree 45% house when it's 80F and 60% humidity outside.

SHS111

Total house 7200 sq ft. First floor 2400 sq ft.

pecmsg

For what its going to cost to operate that 11-Ton A/C consider tightening the envelope first and get the total tonnage under control.

2500 Sq Ft 1st fl in Boston 2 1/2 - 3 -Tons max

Fred

LOL @ChrisJ . I had 15 people over for a cookout on Memorial day. It was 91 outside. Everytime someone went into the house, they'd come out and say " OMG, Fred, I want to live here!" At the end of the day, you go with what works for you. If this homeowner wants to keep his home at 68 to 70 degrees all summer long and he has 7200 sq. ft., old Victorian home, 11 tons sounds about right to me. Sometimes we scare ourselves out of our comfort zone.

ChrisJ

> @SHS111 said:
> Total house 7200 sq ft. First floor 2400 sq ft.
Holy cow that's a bi....huge house!

SHS111

Yes, it sure is. Unfortunately we've fallen in love with it over the years...

ratio

I might be in love with it too!

But now we know that the load calcs are not unreasonable.

Tinman

Coincidentally, 7200 divided by 650 = 11.07 tons. I'd bet dollars to donuts your salesman used a rule of thumb to size your AC. By my definition - amateur hour.

SHS111

So should I hope/expect that the next visit will be more accurate, or should I find another company to give me a proposal? It gets so exhausting.

Jamie Hall

Ideally you would want an actual cooling load calculation, and base the sizing on that.

However...

Cooling load calculations are much more difficult to do accurately than heating load. More variables. So a contractor might be a little skittish about doing one...

Incidentally, your place, @SHS111 , is about the size of the main place I care for, and perhaps about the same age. Fun, isn't it?

ChrisJ

11 tons isn't so insane for that size though.

But there's also a chance 9 tons is plenty.

Fred

I would stick with 11 tons, especially with the 3rd floor. I bet the ceiling up there is right up to the roof rafters and probably not easily insulated (at least not well).

Tinman

I would have your contractor do a heat gain load calculation because otherwise you're just guessing.

ChrisJ

> @Stephen Minnich said:
> I would have your contractor do a heat gain load calculation because otherwise you're just guessing.

This.

And if he's unable to do one, find a contractor that can.

Jamie Hall

Well, folks seem to want a heat gain calculation, on the theory that otherwise you are just guessing. Possibly right, although with all the variables involved in a heat gain calculation the contractor will be just guessing, too .

May I make a suggestion? See if you can get hold of @Bob Gagnon plumbing and heating or @newagedawn to come around and take a look. I think they work in your area.

Tinman

I’m a bit lost. When/why/how is a heat gain load calculation synonymous with a WAG? What, specifically, makes doing an accurate one so difficult?

Jamie Hall

At least in New England, the heat load is as much a function of solar gain as it is of outside temperature. That solar gain, at least in my area, depends on cloud cover and leaf shade. In late May, before the leaves are out but the sun is high in the sky, the solar gain is very very high indeed -- on a roof exposed to the sun, it can almost reach 1 KW per square meter. In july with full leaf cover, that same roof may be lucky to get a tenth of that, or less (this is also a problem for roof mounted photovoltaics, by the way). Cloud cover can change in minutes, with similar results.

What value do you use?

I'm not suggesting that a heat gain calculation is valueless -- it is useful. But it isn't as reliable as a heat loss calculation, where really the only difficult variable is wind load.

Tinman

We deal with similar leaf cover and cloud patterns here in the Chicago area.

Although when the leaves aren't on the trees, it doesn't get very hot here. And while the weather can change in a heartbeat here, on the warmer days things tend to stay very hot. For example, if I'm in a hot attic (something I no longer do) a few clouds passing over isn't going to make it any more comfortable up there. Nor will it make any appreciable difference on the ceiling temperature. If it rains, things cool off in a hurry.

If I have a dense tree(s) on the south or west of the building providing significant shade, I can factor shading into the window coverings. Same thing with a building 3' from another building, which is very common in Chicago.

The reason I argue strongly for doing the math is that sometimes I'm even surprised at the results. When I did new construction, being part of these monstrous homes, there were times when the first floor gain was higher than the second floor gain.

Other times, two similarly sized, small homes having a 1 ton difference in gain. Flat roofs, cathedral ceilings, western and southern exposures vs. east and north, amount of glass, etc.

The 650 btu/h/sf posted by the OP was no coincidence. It's the result of a rule of thumb. Why 650? Why not 600 or 700? What other rule of thumb is the salesman relying on to come up with that number?

Luckily or not so luckily, I've never had to remove a piece of equipment because it was undersized or oversized. I know many who have. That kind of planning, or lack thereof, makes no sense to me.

That said, Jamie. I understand your point.

Jamie Hall

Actually, @Stephen Minnich , I shouldn't be so fussy -- the peak load (high temperature, high humidity) -- isn't likely to be reached except for a few days. Then the question becomes very like that for heating systems -- if you have designed for that, how do you accommodate the lower loads which you have most of the time.

Which is very like the problem with heating systems... which we seem to yammer on about on the Wall a good bit of the time!