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