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Community and Q&A

Upgrading Heating and Cooling System

jr0 | Posted in Mechanicals on

I’m moving into a 1920s house in Zone 5 with baseboard radiators and a single wall-mounted A/C unit.  It has a rather old, low-efficiency natural gas boiler that probably doesn’t have much life left in it.  I’ve found a reputable energy auditor who I plan to hire before I do anything else, and am leaning towards investing in some air sealing and insulation prior to getting serious about heating and cooling upgrades.

I’m also considering installing radiant flooring (and maybe ceilings), at least in some areas: in the case of my finished attic it would be to introduce heating, and in the case of other living spaces it would be to replace baseboard radiators.  While I think I want to do basement waterproofing and air sealing/insulation first, I haven’t quite figured out the sequencing of my HVAC and other house upgrades yet.  My priorities, in order, are interior air quality, comfort, mother nature, and cost efficiency (with maybe 5 to 10 years in this house with which to get an ROI prior to selling).

Some basic questions, to help inform my research and discussions with local pros:

-Is there a significant difference in load requirement for radiant floor heating vs baseboard radiators?
-Can anyone speak from experience about Ecowarm (it seems like a cheaper alternative to WarmBoard, which I’ve found discussions about on this site)?
-(If there is something approaching a generic answer for this): is it typical/wise to account for heating contributions from heat pumps when sizing boiler equipment?  Or do lower operating costs/complexity/disaster preparedness mean I should plan on heating with natural gas alone?
-I’m hoping to repurpose the brick chimney my boiler is currently using as a chase when I get a high-efficiency boiler (which I will vent out a basement window).  Is it practical to run PEX for hydronic radiant flooring up two stories’ worth of a poorly-insulated chase between the basement and attic?
-Am I missing anything important?

Thanks for any help.

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  1. paul_wiedefeld | | #1

    This is a big question! Based on your stated preferences:
    1. ROI is out of the question in my opinion. This will be extremely expensive, I wouldn't count on ever recovering the cost. Most new US houses don't have radiant floors (or boilers in general) and it's much easier to include radiant floors on a new build vs. retrofitting them, so I'd follow the builder's here. Caveat: You can be selective here, adding electric radiant to certain areas (like bathrooms, maybe a kitchen).
    2. Interior air quality: no real gain by going from one kind of radiant to another. Neither option allows for active filtration. Both will be suboptimal compared to a ducted system.
    3. Comfort: Hard to really evaluate, especially since you haven't moved in yet. Air sealing will probably be the most effective improvement in this regard, followed by insulation.
    4. Mother Nature, my most important priority: You can reduce gas usage if using a condensing boiler for sure. It depends on both your home's heat load and radiation type. You'll need to use the lowest water temperature possible, which can be done using radiant floors, but also using existing (or replacement high output) baseboard radiant especially if you lower the load with air sealing and insulation. Dialing this in is difficult before you've moved in and made the envelope improvements. However, consider skipping radiant altogether here: a heat pump(s) (ducted/ductless/both) will likely be cleaner today compared to natural gas. They also can get cleaner as coal leaves the generation mix and allow the option of using your own solar to save money/ reduce emissions. They obviously do a much better job of cooling and actively filter the air, helping with air quality.

    1. jr0 | | #2

      Thanks very much for the input, Paul.

      I was a bit all over the place with my original post, but I'm basically trying to solidify my understanding of factors relevant to boiler replacement before I talk with HVAC pros and energy auditors on-site. Obviously insulation and air-sealing will affect the manual J and sizing for both the boiler and heat pumps; I'm also trying to build as many other factors as I can into the decision about what boiler to get (or perhaps it's even possible to get by entirely with heat pumps). I'm hoping that my water heater and boiler have a year or so of life left in them to allow me to make better-informed decisions regarding comfort, but I doubt it (the water heater is 20 years old; they appear to have been swapping out the anode rod, otherwise it likely would have died already). Hence my haste to shotgun-blast questions.

      As far as ROI, I'm betting that I won't be making nearly enough back on my gas and electricity bills to pay for improvements in 5-10 years for anything other than maybe the air sealing. But I'll consider health and comfort improvements to be an immediate (if intangible) return on investment, and I also think resale value will improve enough to cover most of the upgrades I'm talking about, if I'm smart about it. Probably not the radiant flooring, but my wife likes having warm feet.

      I figured air quality for heat pumps vs hydronic heat would likely be a wash, since the latter doesn't agitate the air or move through any ductwork. But I take your point about filtration.

      I have opted for a tree-hugging power provider, so I'm hoping the cost difference for using heat pumps vice the boiler in the winter isn't too great. It will also depend on what heat pumps and ducts I'm able to get installed; I'm not yet sure what's practical in this currently-duct-free house.

  2. paul_wiedefeld | | #3

    Don’t worry so much about boiler lifetime: the old ones can last a very long time. The water heater is more concerning, but should it fail you can always replace it independently. The sizing will be difficult - anyway you can determine how many gas the previous people used? Boilers come in limited (large) sizes so it’s very likely that the smallest condensing boiler you can put in will be larger than the heat loss by a good bit. If not, not really the end of the world. Most every efficient condensing boiler has a turndown, so a 80k btu max boiler will usually fire all the way down to 8k. So even if you had a 100k max/10k min, you don’t lose much.
    Still very doubtful money spent on a heating system, especially radiant, comes back to you at resale. If it did, all new houses would have it. Insulation and air sealing as well, very few buyers are aware of utility bills at purchase. It should be public, but isn’t.
    In terms of radiant floor, try starting small with electric matts. No need to spend 5 figures on a radiant floor if it turns out it’s not all it’s cracked up to be (the more air sealing and insulating you do, the colder the floors will need to be).
    Retrofitting the ducts will be difficult, no getting around that. There is some creativity to be had with the ductless/ mini ducted minisplits, but it will be a challenge. If more air to water heat pumps were available, this would be a easier project.

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