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Community and Q&A

Updating HVAC System to Include Air Conditioning

MarGun | Posted in GBA Pro Help on

Google brought me here as somebody else was asking a similar question.  First time user, first question right away.  Me, I work as an Engineer in the Marine industry I hold an Engineers License with no Horse Power restrictions. I also have a HVAC License I work with large Refrigeration systems that are not AC. I also to a lot of fabrication skills and have a tool addiction. In other words I know very little about home AC systems.
So I currently have what’s left of a Lennox Complete Heat system.  I have had it since 1998 and have had none of the problems the Interweb loves to get all wound up about.  After 13 years of service with out a hitch I replaced the water heater with a HTP unit only because it was 13 years old. I have 2 Air handlers one for a 1000sf basement with its own Thermostat and the other Air Handler is for 2700sf divided in two story’s above. I have a lot of Windows facing west, 2×6 walls and Brick Veneer. Double Pane Windows and insulation up to year 2000 codes.  When I built the House I installed a separate warm air return from the upstairs incase I ever wanted to install AC.  Since I always spend the Summers in Alaska working I figured I would never need AC, but then I got Married…… Did You guys hear recently it got up to 112 digress in Seattle ? !!!
So I have a number of options. There is no plan to add AC to the basement.
(1) Rip everything out and start over.  Heat Pump HVAC and 2 Natural Gas Furnaces and a conventual Hot Water Heater. This would mean adding 4 more Direct Vent Pipes up threw Walls upstairs and out threw the Brick.
(2) Replace the one Air Handler with a new one that has both HVAC and Hydronic Heat. Keep the HTP water heater and add a Heat Pump. Leave the basement system alone. Maybe You can tell I already like this idea.
(3) Do the above but skip the NG Furnaces and go all Electric. Our  Governor Jay Inslee would be proud of me as He raises our Electric Tax’s again.
(4) Leave everything alone and just add a HVAC unit above my current Air Handler for Upstairs. This must of been the common way to have HVAC back when the Complete Heats were new. I only have 16″ of height to work with.
(5) Do nothing and loose Wife to melt down.
I have two 1400btu potable AC units in the house and on hot days they are just taking the edge off. I figure they are equal to 2 tons. I have installed outside window blinds on probably 40 % of the west Windows. I can not convince the Wife that indoor dark colored Window Blinds are Heaters no matter what the salesperson said.
So going back to option (2) I have found that Ruud and Bosch make Air Handlers that are Hydronic and HVAC.  The Ruud would be somewhat the same size as what I have now. I assume that I can use my current HTP Water Heater  and I do not need the Tankless system sold by Ruud. However I see there are some electronics involved. That means  the two talk to each other ? At some point I might even sell the house. I can already here the inspectors report OMG he still has Complete Heat. This would fix this to.
I would rather try to go with a system out of the box and not try to over engineer everything. That being said I do have a somewhat different situation that really doesn’t come in a box.
Thanx for an ideas.

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  1. paul_wiedefeld | | #1

    Best place to start: determining the heat loss.
    This will help pick between options 1 and 3. You're in a pretty mild climate, so good chance you can get by without backup furnaces. But the heat loss will tell us this for certain.

  2. MarGun | | #2

    I know people who are in my area that rely on an Electric Strip Heater in the Air Handler and say it very rarely gets turned on. In reality my house doesn't take a whole lot to heat. When I built the House it was all about insulation and heating costs. In reality the heating costs are the cheapest utility bill we have. I am since finding out that the energy of cooling the House seems to be greater than heating it. Something that was not even thought of when building it. The House has a View of the Puget Sound and that's why it as a lot of Glass facing west. Seattle is Zone 3 and we are surrounded by Zone 4 on the climate map so it looks like we are a very mild climate. Growing up I remember some days it got into the 90's but most summers only saw 80's. About 10 years ago we had a day it got to 104 and that was thought to be the warmest day of a life time and a fluke. And now we blew that away with 112. In the Winter we may go 5 or 6 days sub freezing in a row but once again it seems to be more common. One advantage of keeping the Hydronic Heat I have now is that I now have two heating sources. One probably not a whole lot more energy efficient than the other.

    1. paul_wiedefeld | | #3

      Sounds like a wonderful view! Plus a well built house, nicely done! The warm air return installed just in case was a great decision. Backup heat is a consideration for sure - but if your blower motor goes, neither hydronic nor heat pump nor integrated electric strips will be of much use. Other options would be electric baseboard just in case, or splitting the basement and other system up so you have two independent systems. Hydronic non-condensing might get you to 85% efficiency, 95+% if it's condensing. A heat pump at your mild temps running at low capacity should have a COP well above 4, so should be substantially more efficient throughout the whole season. The control concerns expressed are a big issue - the best furnaces and heat pumps have modulating blowers. I'm not sure how well a hydronic air handler could be incorporated with this.

  3. MarGun | | #4

    I'm not quite ready to go back to baseboard heat just yet. This is the house I grew up in and I have lived in it for the last 55 years or so. When I started remodeling I ripped out the Coal Shute. Then wile doing foundation work I came to the Oil Line which lead me to the buried Oil Tank that was in the Neighbors yard ! When I moved in at the age of 6 the house had Electric Baseboard Heat with no insulation and huge window gaps. Coats were popular. I switched to NG in 1998 with the system I have now. To keep the theme going I should naturally make the move to a Heat Pump.

  4. MarGun | | #5

    At this point I'm interested in anybody who has used one of the Hydronic HVAC Air Handers. A recommendation as to which one to use or which ones to avoid. I'm really not interested in being the most efficient, or highest tech. A new Air Handler and a Heat Pump outside is a pretty straight forward install. Ripping everything out and stating over would never pay for it self in energy savings.

    1. paul_wiedefeld | | #6

      I think you've answered your question! New air handler and heat pump is as straightforward as it gets (and identical to adding just AC). Keep the hydronic if you can find an air handler that supports it, but it's basically only useful as a complicated backup in this scenario. If not, keep it for the basement only. It adds a lot of complexity for no real benefit in your climate.

  5. kyle_r | | #7

    What about putting in a conventional natural gas furnace with heat pump (or standard air conditioner), taking out your htp water heater and use the direct vent for the furnace. Install a heat pump water heater and don’t heat the basement? Or do cheap electric resistance in the basement. I’m not sure what you are using it for.

    I had a unico air handler on an htp boiler. It worked fine, but I replaced it with a ducted mini split when the air handler gave out. First Co makes some hydronic air handlers that are variable speed. They might be your best bet if you are mixing manufacturers.

    1. MarGun | | #10

      So no matter what I'm going to need a hot water heater so that means using the existing Vent Pipes from the HTP for it. Then if I'm going to add a NG Furnace for up stairs I might as well do the down Stairs at the same time. This means running 4 Additional Vent Pipes up threw the and opening up a wall and out threw the Bricks. And when I'm done the side of the house will look like the battleship Missouri firing a broadside.
      I'm not familiar with a Ducted Mini Split. Wouldn't that just be a normal Heat Pump with HVAC ?

      1. kyle_r | | #12

        My thought was to switch to an electric (heat pump) water heater, no vents needed and have one furnace.

        Ducted mini splits evolved as options to the wall mounted ductless units. They are typically compact units with less air flow and static pressure than typical air handlers. But you can also get large ones. They typically have a lower turndown than regular heat pumps. And many have options for better cold climate heating performance.

  6. Expert Member
    Akos | | #8

    From a quick google, it sounds like what you have a hydronic coil running off your hot water heater.

    If you want to keep this setup, there is no reason you can't keep the hydronic coil replace the rest of the bits with a heat pump furnace (ie Carrier Greensped or Mitsubishi Zuba central) for both AC and backup heat.

    When you want to heat with hydronic coil, run the blower on the heat pump in fan only mode. If you get a very small heat pump, you can even use the hydronic coil to boost the output on those polar vortex days (I don't know if those even happen around you) by running both at the same time.

    Unlike a fuel burner, the good part about a hydronic coil is that there are really no air flow limits. You can play with the airflow to get just the right amount of heat out of the coil to get nice long runtimes in the winter.

    Having written all of that, I think the simplest is probably to deep six the hydronic unit for the main floor and replace it with a decent heat pump. Keep the hydronic coil for the basement.

  7. Expert Member
    BILL WICHERS | | #9

    Akos mostly beat me to it. A typical "air handler" is a blower. If you had a natural gas heater part to it, there would be a heat exchanger / burner assembly above the blower. If you add A/C to that, there is an "A coil" (called an "A coil" because of the shape, but it's just an evaporator) above the heat exchanger. With a hydronic heating system, you'd have a water-to-air coil below the A coil for cooling. I see no reason you couldn't add an A coil to such a system as A coils are often installed within ductwork on top of existing furnace units that act as air handlers when running in cooling mode. I've even heard of people adding water-to-air heat exchangers in gas-fired furnaces to allow an operating mode using an outdoor wood boiler as a heat source to save on heating oil or propane (common in the northeast).

    A heat pump is basically a reversible air conditioner that can run "in reverse" to heat as long as it's not too cold outside. With your system, you'd have your old hydronic system available as "auxillary" (backup) heat if/when it got to cold for the heat pump to operate efficiently in heating mode. That's a nice setup. The complexity will just be in the controls, so you need a thermostat capable of running things, and possibly some logic in the unit itself to know when to do what when the thermostat calls for heat. This could potentially push you into the commercial controls world (where there is a LOT more flexibility compared to typical residential controls), but it's all entirely doable with off the shelf control components.

    2,800 BTU is about 3/4 ton. 2 tons would be about 6,800 BTU. If your existing setup is barely taking the edge off, then it's way undersized.

    You are correct about the blinds. You want something white, or at least light colored. In a pinch, one of the reflective cardboard things made for use in cars can be pushed into service in a window to help with heat gain when things get hot. Simple white paper can help too. You just need something that will reflect most of the sun's energy towards the outdoors.


    1. MarGun | | #11

      Google is giving me a BTU to Refrigeration Tons of 12000 BTU's = to 1 RT. If I punch in 28000 into there calculator I'm getting 2.33 RT.
      We have a bedroom that has dark wooden shutters on the inside. In the summer we are putting Aluminum Foil up to cover the windows and then closing the blinds so we don't have to look at it.

      1. Expert Member
        BILL WICHERS | | #13

        That is correct (12,000 BTU = 1 ton of cooling). I was thinking heating (where 1kw = 3,412 BTU). Sorry about that. I'm used to thinking in heating terms I suppose, since I'm in a heating dominated climate.

        Your OP said two 1,400 BTU air conditioners, which would be about 0.23 tons. That's really small. Assuming the original post was a typo, and you have two 14,000 BTU air conditioners (which probably makes more sense), then you're at about 2-1/3 tons of cooling. If that much cooling (2-1/3 tons), is "just taking the edge off"), then my GUESS is you really need 4-5 tons of cooling for your home. Your A/C system needs to, as I say "win the battle", which means it needs to be big enough to be able to actually bring the temperature down on the hottest day you would normally experience. At some point, the outdoor temperature will reach a point at which you begin to "lose the battle", and the breakover point is where your A/C system can hold the indoor temperature constant, but cannot bring it down. As the outdoor temperature increases past that threshold, the indoor air temperature will start to track the outdoor temperature rise with a fixed differential between the two. This is when I say you are "losing the battle".

        BTW, foamcore (the poster material that is two sheets of posterboard with a foam material in the middle making a product about 1/4" thick) can be cut into nice press-in window insulators that are both reflective (assuming you use white foamcore), and also give a little bit of insulating value, I'd guess around R1 or so. These panels have the advantage that they can be cut to be press-fit into a window so that they are removable and reusable.


  8. MarGun | | #14

    Yes I was off on my Zero's in the original post. I'm planning on a 5 Ton system. Those of Us in the PNW who don't know how to use AC cause we have never had it or a need for it will probably wait till the point of " I can't take it anymore " and want instant relief. I realize this is not the correct way to run it. But its the way we ran our portable AC units when we got them at first.

    1. Expert Member
      BILL WICHERS | | #15

      Note that if you oversize your system, it won't dehumidify very well so you'll end up with a cold and muggy condition in your home. 5 tons may actually be a good fit for your home based on what you're seeing with your existing window units though. The ideal situation is that on the hottest day you're likely to have, your A/C system can just barely keep up and drop the temperature a little bit.


    2. paul_wiedefeld | | #16

      That's a good point - if you waited to use the portable units until the heat was unbearable, that's making them do a lot more dehumidification and cooling then a central AC system would do if it was running for days at a time.

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