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Replacing heating & DHW system

With oil prices only going up, my husband and I are considering replacing our 60+ year old oil burning boiler. Heat is currently distributed via hot water to old cast iron radiators, typically one per room, although there are rooms with none. There is just one water loop, one zone. The furnace is also our on-demand hot water heater. We would like to start thinking about replacing the system with a direct vent gas unit. We added a gas line to the house shortly after we moved in but have nothing tied to it yet. We have a couple of future wish items for HVAC: we would like to have AC system, have the first floor and second floors on separate zones and have the capacity for radiant heat in a mud room and maybe the bathrooms. We may want to also provide climate control to the finished attic but I imagine on using a different system for it. Our hot water needs are currently for the 1.5 bathrooms, kitchen sink, and laundry. A dishwasher is also in our future.
We are interested in energy efficiency, ease of installing the system with limited impacted to the rest of the house and have a limited budget. What type of system would you recommend we look at? The house is approximately 750 sf per floor. We insulated the exterior walls with cellulose when we bought the 1885 house. The windows are double glazed vinyl, c. 1990s.
Thank you for your suggestions,
Wakefield, MA

Re: Replacing heating & DHW system

While I can't speak to the HVAC system, I'll add this;

Taking your best guess, make a long range plan. Do you want extra baths? additions to the house? adding living space? remodeling the bath or kitchen?

Even if you don't do these thing right away, when you do any work it will be under one cohesive plan. Granted, over time your plans will change, but at least it will be less hodge podge as contractors come and go.

Re: Replacing heating & DHW system


Well, Robin, it sounds like you have already done some research on heating systems & you seem to have a good basic grasp of what is required.

I concur with your view on oil prices and strongly urge you to change over to a gas-fired boiler (you have a boiler there) ASAP, because you will continue to pay big bucks for oil, which makes no sense since you already have a natural gas line installed into the house.

Since the current oil-fired boiler is 60+ years old, this makes the changeover even more imperative, since a boiler that old is very inefficient in the way it burns fuel, & is sending 50% of the heat right up the chimney to heat the great outdoors---especially true if the present unit is a conversion job from a coal-fired boiler.

You have an aged heating system that has to be updated; if you do nothing, you will continue to needlessly spend money on fuel oil and an inefficient-burning system, where you can heat the house all winter for 1/2 of what you're spending now---on the other hand, you have some basic essentials that perhaps you should keep---namely, the forced hot water cast iron radiators, and possibly the basic piping distribution system---switch over to natural gas, remove the old boiler & replace it with an efficient boiler by Buderus, Burnham, Triangle Tube, Crown, Peerless, Slant-Fin, or various other well-made brands.

The internal "tankless coil" you have now for hot tap water/domestic hot water (DHW) has to be replaced----do not buy a separate gas-fired water heater for your domestic hot water needs (DHW); instead, you can use the hot water in your boiler to heat the DHW with a companion 40-gallon indirect hot water heater by Triangle Tube, Crown, TfI Everhot, or Weil-McLain G0ld Plus indirect; any one of these makes very efficient DHW for showers, dishwasher, clothes washer & you'll never run out of DHW; the new gas-fired boiler has to be hooked up to your current radiator piping system, but with a new 5-zone (zone valves) near-boiler copper manifold piping arrangement (see caleffi below) that will install separate zones for (1) the indirect hot water heater, (2) the 1st floor, (3) the 2nd floor, (4) the attic, and (5) any other area (radiant zone via a 3-way mixing valve for bath) of the house that needs heat; all these zones would have their own thermostat to give you control over each part of the house---zone valves are inexpensive ($60 ea. + labor), and as many as 10 zones can be installed----Taco 570 series zone valves recommended.

Unfortunately, an important part of a hot water heating system, namely, the piping to & from the radiators, is hidden behind walls, floors & ceilings; if, as you say, the present piping system is a single pipe that connects all the radiators in tandem, this could end up being your biggest conversion expense---to modify the piping system from a single pipe system they usually they have to open the walls at different points & thread flexible hi-temp PEX plastic piping thru the walls & modify the piping arrangements so that you have separate piping for each floor, plus the attic, in one of several piping schemes (see 1st two sites below for piping schemes), called monoflo/venturi, 2-pipe reverse return, 2-pipe direct return, so that zone valves & separate T-stats can be installed on each floor/attic---although a pain in the neck & expensive, it is usually worth the cost & trouble as it reduces unnecessary heating of different parts of the building and greatly adds to the increased comfort & control with the separate T-stats.

The caleffi site below illustrates remodeled piping systems that use supply/return manifolds, zone valves & TRVs; Fig. 3-7 & 3-8 show a 4-zone piping system; Fig. 3-16 shows supply/return manifolds; Fig. 4-7 shows thermostatic (TRV) radiator valves used on rads & baseboard.

I would recommend that you try to keep the cast iron radiators----they give off a superior, long-lasting heat (both convective and radiant) and continue adding heat to a room long after the boiler shuts off---sometimes the heating contractor will recommend you switch to baseboard convectors, because it is easier to create zones & re-pipe long runs of baseboard perimeter heating elements, but they don't put out the comfortable heat you will get from your existing rads---I belong to the school of thought that says it's OK to mix cast iron rads with baseboard throughout the house if this method will help you get zoning on all the floors.

Another decision you will have to make is between the new innovative technology, high tech, high efficiency condensing, modulating boilers that have a heating efficiency of approx 95% (and thus burn less fuel) but are known to be prone to adjustment problems, especially during the first year of ownership; they still haven't ironed the bugs out of many of these units, but Triangle Tube Prestige, Viessmann Vitodens and Slant Fin Bobcat, among others, are considered top of the line---if you have hard water in your area ( a lot of minerals), a stainless steel combustion chamber (as opposed to an aluminum combustion chamber) is recommended; on the other hand there is the tried & true cast-iron standard boiler technology that has been around for decades, as brands mentioned above, that have 85% efficiency & rarely, if ever, need a service call during heating season---the standard cast iron boiler will cost you LOTS LESS than the high tech condensing boiler & is a good option that will save you lots of $$$ on your heating system remodel.

The new gas fired boiler can be vented directly to the outside, but this often creates exhaust fumes in the yard & could interfere with warm weather outside yard activities; better would be to use the existing chimney & run an aluminum flue liner ($200 + labor) up the existing chimney; make sure all exterior walls have blown-in cellulose insulation to R19 in the walls & R40 in the attic (insulation is VERY important--don't skimp on adding blown-in,which can be done for a few hundred dollars)----heavy insulation saves big $$$ on heating bills as well as AC bills.

Also very important, is SELECTING THE RIGHT HEATING TECHNICIAN to do the changeover; consult the Yellow Pages under Heating Contractors---make sure to ask the contractor you call for an estimate if he is familiar with hydronic (hot water) heating systems----get at least 3 estimates (5 or 6 if you have to) until you find one who does a HEAT LOSS CALCULATION to determine how much heat your building needs to keep it warm---70% of existing boilers/furnaces installed are too large for the building heating needs & thus waste a lot of fuel over the heating season (think of burning dollar bills flying up the chimney every time you hear the boiler come on)-----a very rough estimate on the amount of heat you need to heat the house is to take the total square footage of heated space (the square footage of every single room) in the house & multiply by various numbers, such as 30,35, 40; thus a 1700 sq.ft. house would require between 51,000 btu/hr and 68,000 btu/hr to heat, depending on the amount of exterior wall insulation, your location (North Boston) tightness of the windows (replace any single-pane windows with double-pane), tightness of the building, etc.---each house is different, that's why it's imperative to find a good heating technician that will do a HLC and whose installation strategy will coincide with the ideas expressed here; then too, you have a better chance of getting the best price for the job after getting several estimates.

For AC I would recommend perhaps mini-split ductless AC units by Mitsubishi, Sanyo, Hitachi, Friedrich & others; Google "ductless mini-splic AC" to get a list of various sites & price ranges; also Google AJ Madison to get a rundown on mini-splits; another AC option would be thru-the-wall ACs in the 15,000-18,000 btu/hr cooling range for each floor---these are not as quiet as the mini-splits, but they cost a few hundred $$$ where the mini-splits cost $4k per zone; the TTWAC rarely breaks down & is less costly to service & replace.


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