New Heating and Cooling System

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Old 04-14-20, 06:38 AM
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New Heating and Cooling System

Hi all,
Maybe not the right forum for this question but I am trying to cast a wide net in getting feedback about adding a new heating and cooling system to our 1867 farmhouse in southwestern Connecticut. Currently, we have an oil fired boiler that feeds hot water to big cast iron radiators. The furnace is rated for 286BTU for a 2800sq ft house. Windows updated in 1930s I would say, single pane but no drafts, well built. This all got started when we were looking at adding central AC with a contractor we have used in the past on a previous house whom we trust. He suggested if we are adding ducting for the central AC we should consider a gas-fired high-efficiency mod-com boiler to send hot water to coils in the air handlers to also provide heat and move away from the inefficient oversized boiler. Plus we would be moving to gas which we are happy about. If you talk to most plumbers I find they cringe at getting rid of cast iron radiators (CIR), but our house isn't perfect, we have cold rooms because radiators just don't get the hot water to heat up due to being the end of the line and smaller copper line feeds. We feel the new system would allow us some flexibility in modifying our kitchen which needs an overhaul in the next 5 years and is small with a large cast-iron radiator taking up valuable space, the same is true with a bathroom on the second floor.
So thoughts, anyone else heard of using a coil in the air handler to provide heat?
 
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Old 04-14-20, 06:45 AM
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Hydronic forced air is very common. But can be not as comfortable as hydronic radiators.
The first step, either way, is an accurate AHRI load calculation to determine what size equipment will need.
Followed by a manual d for ductwork design.
 
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Old 04-14-20, 08:40 AM
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I cringe at the thought of running ducting for central AC in your house. If you do bite the bullet I would certainly consider central forced air heat as well. It's extremely common and AC/furnaces and package units are common and economical. I like forced air because it makes things much simpler if the power goes out in winter and you don't have to worry about all those water lines and radiators freezing. But the big "if" is the ducting. You might also consider mini splits if you want to add AC without having to open the house up to ducting.
 
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Old 04-14-20, 09:44 AM
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Thanks Pilot Dane. The boss aka wife hates the look of the mini splits and wants central AC/ducting. We don't mind giving up the head space in the basement since it would never be finished and is storage only. Losing the perimeter of the attic for ducting isn't killing the space either. We really desire a more efficient system, the present furnace is a hog at the 286BTUs (with the smallest nosal/orifice for oil on it) for the size of the house. Whatever system gets installed will be based on the heat loss calculation my HVAC company has already performed.
 
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Old 04-14-20, 11:35 AM
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Air ducts do not belong on hot attics.

It's often done in the us but is a horrible idea.

You can look into a high velocity system.

I would keep the rads but change the boiler to condensing with outdoor reset. Hot water can be ran from the boiler to air handler for quick warmups, so you get the best of both heating system types. This boiler can also provide domestic hot water if it has a separate loop for it.

Some rads may not be getting hot enough because they need to be bled - the solution isn't to rip them out!

You should do everything you can to reduce heat loss before putting in new hvac equipment - single pane windows can have storms added, framed walls can be filled with dense pack cellulose, attic and basement air sealed and insulated.





Forced air can be as comfortable as hot water, but it takes a very well designed duct system and not-oversized 2-stage or modulating furnace.
 
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Old 04-14-20, 01:30 PM
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User 10,
Thanks so much for your input and advice. I may have left out some information. We sprayed closed-cell foam on attic walls and ceilings, so that's tight (6" of closed-cell) last spring, made the attic just above the temp of the 2nd floor! The single pane windows do have storms on all of them. We had an energy audit a year ago in December and they further tightened up the envelope.
We have no ducts as of now, but with the install of the AC ducts will be put in. We experienced the high velocity Unico system and didn't like the noise it created or the "jet stream". Since we will be putting in new ducting to carry the cool air in the summer, we figured we would take advantage of those and add the heating component and move away from high priced fuel oil. The current hog of a furnace at 286BTU sucks down the oil and that's with the smallest nozzle on the burner system. That furnace is rated at 80% efficiency.
 
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Old 04-15-20, 10:55 PM
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Forced air heat with ceiling vents will never be close to as comfortable as hot water.
If the house is two story, good duct design is critical for heating the first floor properly from above. Floor level return on first floor is essential.

By all means have ducts put in for a/c.

By all means have a hydronic coil put in the air handler fed by a gas boiler for quick warmups - it can be set up as a second stage of heat the t-stat calls for.

But I really urge you to keep the rads for comfort.

Comfort aside...
Large old rads can work very well with a condensing boiler when the house has been re-insulated.
The lower the water temperature is, the more efficiently these boilers run - the larger the rads are, the lower the water temperature has to be to deliver proper BTUs.

To get proper BTUs out of a hydronic forced air coil, it often takes a higher supply water temperature so the boiler never hits very high efficiencies. (u may be able to get a boiler with a separate loop for a hydronic coil so the radiator loop can be kept at lower temps)

Depends on the coil selected.

see: https://vintagegreenhome.files.wordp...ph_2_w640.jpeg

Do have a room by room heat loss/gain calculation done - used to design a/c system and size boiler as well.

You'll probably be able to drop the boiler btu input down to 80 to 100k btu/hr - 286k btu/hr is huge!
 
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