Price comparison to upgrade from oil to propane combi boiler

[topaz75]

Have a rental apartment over a garage that gets heat and hot water from a 30-yo Burnham RS 109 that is not working properly any more. To avoid the hassle of oil in the future, I was thinking of getting this whole setup replaced with a wall hung, propane combi boiler like the Westinghouse WBRCLP140W they sell at home depot for $2,100

Problem is, I can't seem to find a local plumber to install this. Am still running some quotes through Thumbtack and Homeadvisor.

In the meantime, I have reached out to local heating and cooling companies who install similar setups with Naviens or NTI appliances and am kind of floored by their pricing. I am getting prices quoted in the $9,000 range, which seems crazy to me. Even if their boilers are more expensive and cost $3,500 they are still asking for 6k or so for install.

Does anyone have experience in getting a unit like that professionally installed? What was your price for that?

Or if you can recommend a plumber who would install the Westinghouse boiler (or any other similar one) in south-east Connecticut I would be very interested.

Thanks

 

[Dana]

That boiler is almost certainly LUDICROUSLY oversized for the space heating load of an apartment!

It's minimum firing rate is 28,000 BTU/hr, which is enough heat for a 1800-2000' 2x4 framed house at CT type 99% outdoor design temperatures.

The apartment probably has nowhere NEAR enough radiation to emit even the minimum fire output, so it would likely short-cycle itself into low efficiency and an early demise. This is an issue with all low mass combi boilers, which are better suited to homes with large heat loads an modest hot water needs. An apartment has a modest hot water lows, but also very modest heat load. Read this discussion on the issues of sizing low-mass condensing boilers.

To come up with a more optimal solution, how much radiation does this apartment have?

To come up with an estimate of the actual heat load, if you were on a regular fill-up with a supplier that stamps a "K-factor" on the bill, what are the K-factor numbers? Alternatively, the total volume used between wintertime fill ups would allow you do a fuel-use heat load calculation.

 

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[topaz75]

Dana- thanks for your reply. Interestingly, none of the quotes I got even looked into the issue of heat load, despite being from supposedly reputable companies. They all went for units in the 150-180,000 BTU/h output range. Due to the pricing I received, I am now leaning more towards just replacing the existing oil boiler.

I will have to measure the total amount of baseboard, rough estimate would be around 100 ft total. The apartment is 600 sq ft, built 1957, some insulation in walls and ceiling, but none in the floor, with a somewhat drafty garage underneat. One bedroom, one bathroom, open concept kitchen/dining/living room.

So if I go with an Oil boiler, should i be OK with something like the Slant Fin TR30H? That seems to be the smallest boiler they have that has acceptable flow for the domestic coil. The TR20 only has 2 gal/min which seems to low for even one shower.

 

[Dana]

100' of fin-tube at an AWT of 170F emits about 50,000 BTU/hr. The DOE output of the Slant Fin TR30H is more than twice that much. It's going to do a lot of cycling on space heating calls, and would be something like 6x oversized for the space heating load, with a MISERABLE as-used AFUE.

This the original problem with heating the domestic hot water with a boiler using a tankless coil, and it's exactly the same problem as the wall hung combi units: The peak space heating load is but a fraction of that of the peak domestic hot water load.

The oil boiler has a slight advantage in that with hotter water the radiation emits more heat, increasing the duty cycle. It also has some (but not a lot) of thermal mass to work with. But it has the disadvantage of having no modulation.

If you know the actual heat load of the apartment and the actual amount of baseboard, you can probably get there using an oil fired water heater as a combi unit. At 130F AWT a hundred feet of baseboard can deliver about 25,000 BTU/hr, which a more than 40 BTU/hr per square foot is probably WAY more than the design heat load of a 600' apartment. (I'd expect the real heat load to be half that or less.) It has insulation in the walls, and glass in the windows, yes?


A water heater has an order of magnitude more thermal mass than the boiler and is also better insulated. The heating system water has to be isolated with a plate type heat exchanger suitable for potable water, and a potable-suitable pump on the tank side, a standard circulation pump on the heating system side. The thermal mass guarantees a decent minimum burn time and limits the total number of burn cycles. The flow rates for the domestic hot water can be much higher than with a wall hung combi or a tankless coil too.

The basic topology looks like this:

In your case you could run the water heater at 140F, and wouldn't need the mixing valve on the heating system side. Any new water heater requires a thermostatic mixing valve or tempering valve between water heater and any distribution plumbing going to sinks, showers & tubs though (not shown in the system diagram.)

If it turns out you only have 50' of baseboard instead of 100' it might still heat just fine at a 140F storage temp, but in the event that it doesn't it would have to be bumped up.

Just about any Everhot or Bock would be suitable for this application- you don't have to spend more than about a grand for the basic unit.

The comparative efficiency of this approach can be seen in this document. See Table 3, system 6, and Table A6.2 appendix #6. Note that they stop at 3x oversizing in Table 3, but the fall off in efficiency is much steeper as the oversize factor increases. The basic test was done at a much higher water temperature than normal domestic hot water temperatures with the presumption that the heating system needed higher water temperatures. Table A6.2 demonstrates that efficiency soars at lower temperatures. Stay within the manufacturer's low temp limits (if they have one), but if there's really 100' of baseboard the system will never need 140F water, so the tank will never have to be run at 150F & up to deal with the temperature drop across the heat exchanger.

It's at least as efficient as a 3x oversized boiler with a tankless even when running at 150F and higher, but it can be dramatically more efficient if you run the system at domestic hot water temperatures.