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Ideas to gas heat & DHW a 450 ft apartment with moderate cost and maintenance?

Jells Member Posts: 505
So I’m finally going to add real heat to my last ‘gas on gas’ apartment, on floor 3 of 4 in a 120 year old brick, uninsulated ‘tenement’. These 450 sq ft units were built as cold water flats. Previously tried 2 decades ago was a Minitherm boiler with an indirect tank: big footprint, clanky to have in your living room, and often needed resetting due to some venturi effect from being on the top floor. I pulled it out.

Installed now are 4 systems based on a 40 gallon DWH with a bronze circulator pumping 140 deg water through hydronic baseboard. Several years ago in one top floor unit I supplemented the radiation with 2 kickspace heaters. That one has a total radiation @140deg of ~18k btu, the others ~9k. A 6th unit was converted to the upper floor of my own unit, with total peak radiation of ~13k off my 180 deg boiler, but it’s zone cycling is fairly low.

So far the biggest downside to these is potential water damage from tank failure if the pan and leak detector device fail. Maintenance is very low. But I’m open to new ideas, for this last one and the others as the tanks fail.

Heating Contraints:
Can’t vent through the brick side wall, it’s on the property line. I have a huge flue for the original coal burning stoves on each floor.

I have a ¾” gas pipe running 55’ from the basement meter to where the heat will be.

I do not have a drain where the heat will be for condensate, it would have to pump up, through the ceiling over the bathroom and down to the kitchen drain somehow.

I’ve been told I should be using a heat exchanger on the current systems because of Legionella risks (local contractors & vendors poo-poo this). So if I am simply reproducing that system, any advice on this improvement would be useful. I was looking at simple exchange blocks, but they have a temp drop rating that concerns me since I’m already at low btu throughput. Or is that irrelevant due to the low emittance relative to the heater btu? That once it’s circulating the block can maintain high temp transfer since it’s being asked for relatively little ∆T?

Other than that, it looks straightforward. The rad loop system is set up like a boiler’s with a circulator, pressure reducing valve and an expansion tank with an air scoop. The DHW side is like I already have, just needs a circulator loop with check valves and an air vent, and that one runs 24/7 year round to not let the water in the loop cool and stagnate.

I'm considering doing away with the baseboard in this one and just using kickspace heaters in wall cabinets. It's easy, and in a tiny apartment the baseboards reduce usable space. Downsides?

I don't think this is a good radiant candidate, in such a small space, there isn't that much unobstructed floor.

A mod-con system is fascinating, but many of it’s virtues do not hold up with a rental. The efficiency vs maintenance seems to make it less appealing to me, even my plumber agreed after some discussion. The difficulty of venting is another problem. I’d need to drop the vent and air pipe 20 ft from the roof through the flue and somehow connect to it through the brick flue wall. It would be a trick getting rid of the condensate, and I’m not even sure I have enough gas for the on-demand DHW. The unit itself is 3-6x the cost of a 40gal atmospheric vent DWH. Is there something I’m missing?

Speaking of water heaters, can anyone explain the advantage of the ones with side taps for space heating? I have some with, and some without. I’m not talking about the ones with an internal heat exchanger, just the side taps.

I know this is overlong, but I didn’t want to make like 4 different threads. Any advice is welcome! Thanks for reading this far.


  • hot_rod
    hot_rod Member Posts: 18,209
    Rheem offers those combined systems with tankless heaters. Look like they have both condensing and non condensing options. This system lowers the water content compared to the tank type combined systems

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jells
    Jells Member Posts: 505
    @hot_rod I am familiar with that type, but I'm having a hard time coming up with a compelling reason to use it versus the hot water tank system. Relative downsides are higher cost, difficulty venting and draining condensate, and higher maintenance vs bigger footprint and tank failure potential.

    It's harsh to say it, but as landlord I'm not really driven to provide the most efficient heat system, and this little apartment isn't very expensive to heat anyway.
  • PerryHolzman
    PerryHolzman Member Posts: 234
    edited January 2021
    IF a normal sized hot water heater is effectively heating these units.... while supplying hot water. Its likely on the small end for a boiler.

    From a cost and maintenance standpoint: Water Heaters may work just fine, and a high quality water heater is likely to last as long, or longer, than the lower end boilers. You do need to install that heat exchanger for heating and build a small heating circuit with and expansion tank.

    If you have a number of apartments. I might just buy a spare water heater and have it in the basement storage as something that can be installed instantly if needed. I like having parts on hand... Not likely a major issue if you live in a large city (I do not).


    PS: if you are looking to get away from the chimney - and if electric rates are reasonable. You can get electric boilers (and electric hot water heaters too). Electric boilers are usually cheaper than fired boilers - very reliable and easily fixed if you stick with a known Mfr (and stock a few parts).
  • Jells
    Jells Member Posts: 505
    @PerryHolzman Thanks. I do live in a big city, getting stuff is not usually a problem though the attrition of plumbing suppliers has been startling over the last decade. I'm dubious about the whole 'high quality' 12 year warranty thing, I've heard you're not actually getting a better unit, just essentially paying for an insurance policy on the same damn heater!

    One of the units is a 10 year that just turned 10. I'm thinking of replacing it proactively. The cost and labor doesn't bother me, it's getting those damn things up and down from the 4th floor! It's funny that during the narrow window between my son getting big enough to help and going off to college I never needed to replace one.
  • PerryHolzman
    PerryHolzman Member Posts: 234
    edited January 2021
    Jells said:

    @PerryHolzman Thanks. I'm dubious about the whole 'high quality' 12 year warranty thing, I've heard you're not actually getting a better unit, just essentially paying for an insurance policy on the same damn heater!

    Look at how the heater is constructed. Plain Steel tanks don't last long (even if painted), and I'm not sure anyone offers them anymore. Glass lined steel was the older industry standard, and now you are seeing ceramic lined tanks introduced within the the industry standard for residential hot water heaters.

    I believe some mfr's supply tanks from SS - at least at the commercial level (although you are likely going to have to order it). Viessmann supplies at least indirect water heater tanks (to be used with a boiler) made from 316 T SS - which will likely last forever (my Viessmann water heater tank has a real "lifetime" warranty - and I doubt that Viessmann has ever had to replace any).

    "T" = Titanium, which prevents carbide formation & eventual cracking at temperatures typical of hot water. Titanium just works much better than any other additive or modification to normal SS's to prevent carbide formation at the temperatures involved, unless you go into the super-ferritic SS's which are very expensive and I cannot imagine being used for this application.

    I would still expect any SS tanks to last longer than a coated steel tank.

    You might wish to ask the supply houses in your area if anyone has a SS water heater tank available (and get the technical details to find out the allow. Anyone using 316 T is likely going to list that in the brochure. Expect to pay more for a SS tank.

  • Jells
    Jells Member Posts: 505
    @PerryHolzman stainless would be fantastic, no doubt they're not common because then people wouldn't be buying new water heaters every 6 to 12 years!
  • mattmia2
    mattmia2 Member Posts: 7,171
    HTP makes some electric and some condensing gas stainless water heaters as well as a few combination heating and hot water appliances(all of these might be worth a look). I don't think they make a natural vent stainless tank. The grade of stainless that most manufacturers use is affected by water chemistry, especially chlorides, so you need to check the specifications and your water before deciding to invest in something for longevity.

    The longer warranty tanks frequently are the same basic tank as the standard model but they have better quality accessories such as additional anode rods and sometime better drain valves. What I would do is buy the standard tank and either a second anode that installs in the tank outlet or a powered anode and I would buy a real full port ball valve with hose thread and cap and a brass nipple to replace the drain. I would use the powered anode in my own home where I can monitor it to make sure it stays powered, in a rental unit that could be a challenge. You also may want to get a tank with commercial controls that can be set above 140 degrees to kill legionella and put a tempering valve on it to cover your liability for both legionella and for scald injuries.
  • Jells
    Jells Member Posts: 505
    Thanks @mattmia2.  I always use a tempering valve, but I didn't know there are any tanks that could be set to higher temperatures.