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Efficient way to combine forced air and radiant heat?

gigik Member Posts: 2
Hello, I'm in the midst of a full gut renovation of a brick loft in the midwest, and am looking for advice on the most efficient way to design our HVAC system. To provide background, the building was built in the late 1800s and converted to residential condos in 1996 (6 units overall), and used a forced air heating system. The brick walls are about two feet thick and remain exposed in most areas of the units. Our particular unit is a duplex on the ground level, and is about 2200 square feet overall. It consists of the ground level (640 SF) and attached garage, a mezzanine above the garage (460 SF), and the top floor (1100 SF). The unit currently uses two furnaces and two air conditioners for heating and cooling purposes, which we will be replacing in the renovation, along with the ductwork. While working with our architect on the plans, we asked about radiant heating and they advised that this was really only beneficial when you're pouring new concrete, which was not conducive to the current state of the unit. They said the electric pads were pretty expensive to run and don't last long, so we dropped the idea. Now, due to some structural issues uncovered during demolition, we have to have the flooring of the top floor bathroom replaced, so I was hoping we could possibly do some of the hydraulic piping in the new floor when it's poured. I asked a plumber his thoughts, and while we didn't discuss it too thoroughly, he said it could be possible if we wanted to maybe do a combi-boiler? With the research I've done thus far, it doesn't look like that's too common / might possibly be overkill? My thoughts are that I'd rather do something costly upfront if it is going to provide a lot of benefit down the line (rather than regret not doing it later on), but even with cost aside, I'm not sure if it would end up causing us more headaches if the installation wasn't absolutely perfect.

Just to provide some additional insight if necessary, this is a total gut, including full plumbing and electrical upgrade for new kitchen, three full bathrooms, all new HVAC, etc. Ceilings on the top floor are 12 feet, mezzanine are 7 feet, and bottom floor are 15 feet. Right now, the plan calls for two furnaces, two air conditioners, and two tankless hot water heaters (unless we were to go the combi-boiler route).

Judging by the research I've done, it seems like it would be an insane and possibly nonsensical thing to do, but my concern is doing the construction the right way from the beginning, and I am just a bit fearful that the high ceilings are going to give trouble in the winter with the forced air. Any insight would be greatly appreciated, and I would be happy to provide more details if needed.


  • Steamhead
    Steamhead Member Posts: 16,459
    You don't necessarily need to be pouring concrete to do radiant. First thing to do is a full heat-loss calculation on your unit. The entire system design is based on that.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 22,147
    As @Steamhead notes, you don't have to be pouring concrete for radiant. There are other ways to do it which work just as well. Also, as he says, the very first thing to do is to do a room by room heat loss on the unit. Without that pretty much any installation is doomed to be at best mediocre.

    You do need the ductwork for the air conditioning. However, I would give very serious consideration and thought to radiant floors in the whole unit, powered by a mod/con boiler (if you have natural gas available) or a high efficiency oil boiler, with additional heat if needed by a heat pump -- which would also do the air conditioning. Your heat loss calculations will tell you if this will work.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,537
    Your architect is not the person to be discussing the feasibility of radiant in your project. That assumption is based on the answer they gave you when asking about the radiant heating option.

    As been said you need to find a competent designer /installer for radiant systems to do the load calcs.
    HVACNUT Member Posts: 5,476
    Along with what the others have said, if its feasible, with the high ceilings, you can put down a sub floor, vapor barrier, then finished floor over the radiant tubing. You could lose up to
    2 1/2" so the mezzanine is a concern.
    A 2 stage thermostat with heat pump back up should work. You could also ditch the tankless water heaters and zone an indirect off the boiler.
  • gigik
    gigik Member Posts: 2
    Wow! Thanks for all of this information! So, based on the responses;

    @Steamhead, We are located in Chicago. We haven't had any full-heat loss calculations done in the unit since the initial plan was just to swap out current furnaces/AC's/ductwork with upgraded versions.

    @Jamie Hall, Ductwork will always be required for air conditioning, no matter how the unit is heated, correct? If that's the case, that's a relief. I was under the assumption that if you heated the entire unit via radiant floor heating, you would only use the ductless systems for AC.

    @Gordy, Unfortunately, there seem to be many, many things that have been ill-advised from our architects. We are relatively young and this is our first renovation, so we thought that taking precaution in vetting a multitude of talented architects would help us start the project off on a great foot to do it right, but we're in a pretty big bind right now. At this point, I'm not even sure how to vet HVAC contractors, because I'm receiving so much misinformation, and I really don't know how to find a competent radiant designer/installer (just by my initial research online and in meetings, the radiant in this area almost seems like an afterthought - can't really get a good read on it, but I might not be looking in the right places, of course). I thought if I could narrow down whether this would actually be feasible for the unit, I could go into things better prepared and with a clearer vision of what we want to do.

    @HVACNUT, With regards to the ceilings, two things; 1. The top floor (12 ft ceilings) is mainly made up of some very old and very amazing 2-inch thick pine flooring that we uncovered in the demolition that we are going to just keep as is. I don't know what goes into retrofitting, but we've removed almost 80,000 pounds of debris so far, and it was just one of the one things we felt relieved to not have to touch essentially. The top floor is also where we will be pouring new concrete for about 225 square feet of tiled area (first bathroom). 2. The bottom floor (15 ft ceilings) would be fine for the additional 2 1/2" - but yes, the mezzanine is cutting it really close as it's only about 7.5' in height with barrel-vault ceilings so to cut in even more would be iffy (also the location of the second bathroom and laundry). That mezzanine is above the garage, so the floor below doesn't matter. However, there will be a slightly smaller mezzanine across the room that will hold an office. Below it will be a mud room and the third bathroom, so we need to take height considerations there, too.

    -Based on this, is there anything else that kind of stands out with regard to the systems or even ways to approach/discuss this with a designer/installer? Like I mentioned, it's been so much time and money already, but I'm really looking to do it right from the get go, and after two years of not being able to live there, I don't want any shoulda, woulda, coulda when we finally move in!
  • Gordy
    Gordy Member Posts: 9,537
    edited June 2017
    Go to find a contractor here on this site main page.

    There is a huge difference between architects,engineers, designers, and installers.

    There is always feasibility for radiant even if it needs supplemental emitters.

    When thinking about radiant don't forget walls, and ceilings . Also if supplemental emitters are needed panel rads, and towel warmers.
  • Canucker
    Canucker Member Posts: 721
    In Chicago? I think @Stephen Minnich might be in your area
    You can have it good, fast or cheap. Pick two
  • hot_rod
    hot_rod Member Posts: 20,790
    Here is your guy in the Chicago area.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,537
    Yes, yes Stephen is your designer/installer!
  • ChrisJ
    ChrisJ Member Posts: 15,162
    Highly recommend Minnich Mechanical. They're the best in the business.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • cnmdesign
    cnmdesign Member Posts: 103
    Combat Veteran owned, Final Salute LLC on FaceBook & Twitter.
  • Henry
    Henry Member Posts: 996
    Here is a combination of geothermal, boiler, forced air, radiant, hotwater via indirect and a 500,000 BTU pool heater. You need somebody that can do the heat loss and then properly design the system.
    This system has been running with NO repairs since early 2012.