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Multifamily - replacing an old oil system with gas - single system or separate?

napnap Member Posts: 9
Owner occupied 4-unit multifamily here. First time posting! Could really use some advice... getting very different opinions from different contractors...

We bought this 4-unit in Maine last year and the ancient oil boiler barely made it through the winter. Time to replace it! Fortunately, Unitil (local natural gas provider) has gas available on our street and will run a lin to the house for no charge. Can't see any reason to stay with oil so I guess we're switching. But the question is 1 system or 4? And we're looking at replacing the hot water tanks at the same time as they're all past their expiration date as well.

Current situation: Forced hot water throughout the building. Already separately zoned though. Thermostats in each unit. Tenants each currently pay for their own hot water (4x ancient electric hot water tanks) but heat is included in rents. Also maybe important to note: we have low water pressure on the street/main for whatever reason, so there's a pump/booster installed...

We're looking at two different options I think but I would LOVE to hear from you guys on what you recommend... honestly it's been really hard to comparison shop here as the contractors we've spoken with are all VERY opinionated about the one option they would prefer to do... thanks in advnace!

Option 1: Single high efficiency gas boiler with a single indirect hot water tank for dhw. The contractors we've spoken with have said a 75G tank should be sufficient but I'm skeptical given that the 4 individual hot water tanks they'd be replacing are 40G each? Is it a mistake to install a single system, and moreover to move to a single hot water tank if we go this route? It is certainly the most cost effective option.

Option 2: Install 4 meters. Install 4 combi units (quoted veissman wall-hung units by a couple different contractors). This seems ideal if we were ever going to sell though I suspect that isn't any time in the near future. I do like the idea of tenants paying their own utilities but at what cost? This is literally 2x+ the price of the other option, and I'm concerned about the maintenance cost from what I've been reading about combis. I've also read in various places that low water pressure may be an issue?

All suggestions / opinions very much welcome. Thanks in advance for your thoughts. This is a major expense for us so we want to make sure we fully understand the tradeoffs and are making the best (e.g. most responsible) decision given the information we have.

Comments

  • Lyle {pheloa} CarterLyle {pheloa} Carter Member Posts: 23
    As for the single boiler option, it all depends on how you feel when see one of your tenants with the window open during January or February.
    As far as maintenance concerns any high efficiency boiler is going to require annual maintenance.
    For the multi boiler option I would recommend a high efficiency boiler with a fire tube design, they seem to be far less likely to accumulate debris. And indirect water heaters, with the indirect water heater the annual maintenance is at a minimum, compared to a Combi.
  • Jamie HallJamie Hall Member Posts: 13,871
    I'm not a bit surprised that you are getting different answers from different people -- since it is much more of an economics and property management question than it is one of how to heat the place.

    Therefore... it really has to be treated as an economics question.

    In either scenario, I'd be inclined to use a properly sized (or four properly sized) mod/cons, firing an (or four) also properly sized indirect tanks (I don't think 80 gallons is big enough for a four unit building, though, so you might need two... last thing you want is the fractious lady in apartment three running out of hot water!). The economic and property management tradeoff is that with four units, you an bill each apartment directly for the heat they use -- it's very straightforward -- and tack the maintenance into your rent. With one unit, you have less maintenance (by a factor of four!) and you've sunk less capital (that gets recovered in the rent, too), but it is much more diffiult to charge separately for the heat, so you go "utilities included".

    Then there is the question of what sells in your area -- are most places utilities included? If so, you might want to go with the crowd. On the other hand...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    HVACNUTnap
  • IronmanIronman Member Posts: 5,925
    edited August 2
    Here's another option to consider (though I would lean toward 4 separate systems): if you keep it as one system, then I would look at using two smaller mod/cons twinned together and two larger indirects as Jamie suggested. This way, you have redundancy if one of them goes down and you also have the ability for one to heat the indirects while the other is space heating. It would also be more efficient because the turndown ratio would be doubled.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rodhot_rod Member Posts: 14,080
    I'd also twin two mod cons for 22-1 turndown a couple 120 indirects, or plate HXers for DHW.

    BTU meters are an option, there is an ANSI standard now, so you can bill according to actual use.

    DHW could be produced by 4 plate HX also run through the BTU meters. This is a common way that multi family buildings are billed from district systems. So tenant pays for heat and hot water.

    Some heat metering examples and reading here.

    https://www.caleffi.com/sites/default/files/file/idronics_24_na.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    nap
  • napnap Member Posts: 9
    Thanks for the feedback! And good to know that indirects are a good option.

    Re sizing for that: one contractor quoted us the 80G tank and told us he had used the same thing in a 6-unit without any issues so it would be more than enough for our 4... but I'm still skeptical. Don't want anyone (including ourselves!) to run out of hw. Are two indirect tanks preferable to one larger one? That cost would begin to creep closer to the 4 separate systems...

    Re tenants and utilities... each unit already has its own thermostat so I'm not super concerned about open windows in January. Saving some money on the boiler replacement would allow us to replace a bunch of the windows also, many of which are in bad shape.

    tbf if this were a pure investment property that we weren't living in, I'd be more concerned about the one system with utilities included, but as it's owner occupied it isn't my biggest concern. I imagine that it might make resale easier some day (as the next owner might not be oo) but we have no plans to sell any time in the near future.

    As for the local rental market, it's a pretty sloppy split between utilities included and not included... so it's not uncommon. Could go either way. Have to admit the single system is tempting purely because it is half the price :neutral:

    For the 4-systems approach two separate contractors have both suggested the Veissmann Vitodens combi units.

    For the single unit approach, we've received quotes on a Bosch Greenstar FS 151 and a Weil-McLain GV90+.

    Is there any reason to be concerned about the water pressure issue I mentioned? From the reading I was doing, that was one of my largest hesitations about the combis (other than things I've read about lifetime and maintenance of those units).
  • Jamie HallJamie Hall Member Posts: 13,871
    The water pressure issue shouldn't be a problem with the combis, so long as your booster comes up with at least 30 psi or so going in. The head loss through the domestic side isn't all that great, so you should be OK.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    nap
  • Larry WeingartenLarry Weingarten Member Posts: 1,955
    Hello, It's sort of heretical thinking, but if the apartments aren't too big and the floor plan is agreeable, have you considered just using wall furnaces and possibly heat pump water heaters? Individual metering will most likely be appreciated by a future owner and it's been shown to help people curb their appetite for energy. There also may be some incentives for going with heat pumps: https://www.dsireusa.org/ Just saying. o:)

    Yours, Larry
    SuperTech
  • egansenegansen Member Posts: 25
    I am just a home owner but lived in apartments in college.  One thing to consider with individual boilers for each unit is what would happen if the tenants don't pay the bill and the gas gets shut off?  Would the pipes freeze and burst causing damage to the building?

    I remember hearing horror stories about how students would turn the heat all the way down when they would leave for breaks, pipes would freeze and burst flooding the apartment and the ones below.

    With one system you would not have the potential for this issue.
  • hot_rodhot_rod Member Posts: 14,080
    It really come down to how the occupants use hot water. If everyone tries to shower at the same time I doubt an 80 would be adequate

    Any tubs? That is considered a dump load that would need storage to cover.

    Experience tell me that people will use all the hot water you provide, be that 80 gallons or 350.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • JUGHNEJUGHNE Member Posts: 7,436
    If you were to go with 4 heating systems are all the return pipes accessible in the basement for separation?

    Also if you go with 4 mod con units is there approved wall space for exhaust piping to leave the building....sidewalks....adjacent buildings etc.

    IIWM, I would just stay with electric water heaters, maybe 50 gallons......looking at future replacement and maintenance.
    Tenants already paying for hot water.

    Down side is minimum NG payment (by tenants) during summer of non usage of gas.
  • PerryHolzmanPerryHolzman Member Posts: 153
    I'd vote for a single overall system that used multiple (2 or 3) staged boilers to supply it.

    That way when 1 boiler needs service (or fails) the other(s) can still provide heat and hot water.

    The entire system can run very economically during the heating system because the efficient range of operation is far larger.

    The controls can also rotate which boiler fires first to even out the use.

    I cannot speak to the size of hot water storage.

    I personally like the Viessmann boilers. I'm glad that you have contractors who also like them; as its the contractor who makes or breaks a boiler and system install.

    Perry
  • napnap Member Posts: 9
    The return pipes are accessible, yea. From what I've been told it'd be a relatively easy conversion if we were to go the 4x combi route. Venting for that configuration (wall-mounted combis) would be to the left side of the house, which is adjacent to our neighbors driveway. Contractors didn't seem to have any concerns about that. A single floor standing boiler would instead vent through the chimney, which would need to be lined as I understand it.

    Thinking about the size of a storage tank for the single system... it occurs to me that our water pressure is probably a more limiting factor than the hot water storage size. If 2 people are taking a shower and someone is also running the laundry, our pump is working overtime, and the water from the tap is a trickle. It's been tough to find someone who can address this fwiw. Maybe we just need a larger pressurized storage tank for our water pump (aquaboost II + well-x-trol tank). That's what had me worried about the combis in the first place.

    Just to be clear, we're coming from a single ancient oil boiler, with 4 separate electric hot water tanks. I don't mind sticking with the electric hot water tanks, but 3 of them are well past their expiration date and I figured we'd just do it all at once if there are more efficient (combi or indirect) options available to us at this time.
  • hot_rodhot_rod Member Posts: 14,080
    If your decision is based on $$, and the tenants pay the electric bill, then stay with electric water heaters for each unit. Maybe consider a marathon or other lifetime type.

    Looks into a variable speed pressure booster like a Grundfos Scala. it eliminates the need for large pressure tanks and varies the speed to match the load. As long as you have an adequate main line coming into the building to supply the pump :)

    https://us.grundfos.com/products/find-product/SCALA2.html
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    nap
  • napnap Member Posts: 9
    Thanks for the tip about the Grundfos. I'll bring it up with the plumbers I'm speaking with. tbh most of them I've spoken with seem to know little to nothing about these things. I *assume* the main is adequate but I'm not the expert. I know a number of other houses on the hill also have pressure issues and require similar equipment.

    The other issue with 4 separate hot water tanks is simply the space they require. We have a tiny basement (2/3 of our basement/street level is an apartment) and were looking forward to freeing up the space. But it would certainly be less work and more cost effective (in terms of up-front) to stick with the tanks that are there and replace them when they start to go I suppose... 3/4 of them are > 10 years old as it is. I figured we'd do a small bump in the rents next cycle if we move to paying for hw and eat it in the meantime.
  • Jamie HallJamie Hall Member Posts: 13,871
    If there are other buildings in your area which are having trouble with low water pressure, a booster -- such as the Grundfos mentioned -- may not be able to help much. They -- and, for that matter, any pump -- require a certain minimum pressure at the inlet to avoid damage to the pump. You can check this -- though with a bit of hassle! -- if you have a way to measure the pressure in your water main before the booster -- possibly a hose bib or something? Put a pressure gauge on it and see what it reads when you are drawing a lot of water -- and I'd say that anything less than 10 psi is a real problem, and one which a bigger booster or variable speed booster isn't going to fix.

    Now. That is really a problem for your water supplier. In theory it is their responsibility to provide you with an adequate supply of water at a reasonable pressure.

    Right. Good luck with that.

    There are ways to overcome the problem -- my relatives in Scotland have been coping with this for decades! as have any number of rural properties on low yield wells. Trouble is, the ways involve providing enough storage volume to handle the peak flows. There are several different ways to do this, depending on the situation -- I can give you more info, if you need it.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    nap
  • hot_rodhot_rod Member Posts: 14,080
    UPC plumbing code requires a min. 15 psi. If the pressure at the main drops below that, I would contact the provider. I would think they are required to provide a minimum pressure? Any fire hydrants on the street?

    If pressure drops in your home under a high flow condition it could be the line from street to home is scaled partially shut, or a valve not fully opened. This is a flow issue more then a pressure issue.

    Install a gauge at your building, with nothing running that is static pressure. Watch pressure as facets open, dynamic pressure.

    Those "smart" pressure boosters have features to protect themselves and a run dry lockout, should the supply not be adequate to the pump.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    nap
  • SuperTechSuperTech Member Posts: 1,479
    I like the idea of two EK boilers with Carlin EZ gas burners. Use two large storage tanks and the plate heat exchangers should be able to make plenty of DHW. Less maintenance than the mod cons and probably longer lasting. Reliable, quiet and efficient. 
  • napnap Member Posts: 9
    I will definitely call the water district again about the water pressure. Maybe the last person we spoke with there just wasn't clued in or helpful. Never know. I don't think I've ever seen it dip below 15 PSI but that's not a lot of pressure...

    I'm currently leaning towards doing the single system at the moment, mostly based on some of the concerns I've heard from other local landlords about their combi systems. As some here have pointed out, a single system means there's less that can go wrong :). Spoke with my realtor (also owns and manages several similar multi-families in the area) yesterday who encouraged me to save the money and go with a single system also and just keep rolling the costs into the rent. Still debating but definitely leaning that way as of today. Thanks for all your feedback everyone.

    If we do go that way I'm still wrestling with the 4 electric tanks vs a larger consolidated indirect tank. It feels weird to have a system that requires the boiler to fire in the summertime, but it sounds like it's more efficient regardless of that? (and that the time to refill is much quicker, so the smaller tank isn't generally an issue) Is that correct?
  • IronmanIronman Member Posts: 5,925
    The indirect, operating with a gas boiler, will be much cheaper to operate.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
    nap
  • STEAM DOCTORSTEAM DOCTOR Member Posts: 1,253
    In my part of the world, the number one tenet related issue, is heating relate . Tenants want to feel like they are in Hawaii and landlords want to pinch pennies. Got heating call once. Landlord was out of state. Said that tenant called to complain that not enough heat. Was about 15 degrees outside. Came down to house. Thermostat was set for 85 and all the windows were open. Best way to avoid these problems is to give each tenant their own heating system and have them each be responsible for paying for their own heat. Maybe install a second thermostat in parallel. Second thermostat should be set low and will only be there to prevent freeze ups. 
  • hot_rodhot_rod Member Posts: 14,080
    With BTU meters every tenant pays for exactly the amount of heat or hot water they desire. A single boiler and a 120 indirect with a large coil, or dual coil for quick recovery.

    I can't imagine anyone showering with 15 psi out of a 1.5 showerhead? But if so, you should not go thru a lot of HW :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
    nap
  • EdTheHeaterManEdTheHeaterMan Member Posts: 1,049
    edited August 8
    @nap
    Atmospheric boilers like the Utica, MGB, the Crown (Velocity Boiler Works) CWI or US Boiler series 2 are the simplest boilers to operate. All the boiler manufacturers have the "economy model" Very few parts to fail. In many cases, they can be retrofitted with old analog controls if the electronic S*** fails, for a lot less then the repairs needed when ModCon boilers fail.

    The cast iron boilers last forever and the smallest model in the series should have no problem handling the load. The efficiency is not over 90%, but if the tenants are paying the bill, the small boiler will be affordable.

    I'm in favor of leaving the electric water heaters there if they are already zoned for each apartment. As each water heater fails, replace it with a standard 30 or 40-gallon atmospheric gas water heater. So make provisions for 4 boilers and 4 water heaters in the chimney with the proper liner size. Four 50,000 boilers and 4 40,000 water heaters in one chimney would only be 360,000 BTU

    As an economics problem, the boilers are lower priced than ModCon, lower maintenance and service cost, and the small boiler is affordable to tenants. And you are not paying thousands more for equipment that will save tenants money in operating costs.

    Who of my esteemed colleagues can say that the 30-year-old cast iron atmospheric boilers with standing pilot were the most dependable heaters out there... that is how the Natural Gas Companies stole all my father's oil accounts in the 70s, 80s, and 90s

    That's me thinking like a landlord.

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