Boiler Temperature

[Scott McNab]

So 20 minute burn, off for 20-30 minutes and repeat cycle is ok? That's with a -20 degree celcius day. Warmer days the idle times are longer. No matter the outdoor temperature, the burn time is always 20 minutes to satisfy thermostat.

 

[Scott McNab]

What can I do short of replacing the boiler if I don't have enough emitters?

 

[Sponsor]

 

[Dana]

If it's actually burning for the full 20 minutes rather than cycling during the call for heat you have enough heat emitter for the boiler at it's current burner settings.

A minimum burn time of 20 minutes is excellent from an efficiency point of view.

If it's maintaining 20C indoors and the thermostat is calling for heat 20 minutes then off for 20 minutes (~50% duty cycle) at -20C outdoors you have enough burner and enough emitters to heat the place down to about -60C outdoors.

Is the temperature swing large enough that it's bothering you? If yes it can be replaced with something with less of a temperature drop before calling for heat again, or one that has a programmable swing. The duty cycle will be the same, but there will be more burns/day. The lower the temperature swing the shorter the cycles, but 10 minute burn cycles are every bit as efficient as 20 minute cycles, and 5 minute cycles take efficiency hit of around 1% compared to 10 minute cycles. At shorter than 5 minute burns efficiency starts dropping ever faster.

 

[Scott McNab]

It maintains 18 degrees. House isn't insulated great so any warmer would likely get quite expensive. I'm just used to oil so it seems like I'm burning a lot of propane. Seems I'm worse off. Temperature swing doesn't really bother me. It does drop 1 degree as the boiler is burning until the circulator kicks on. With it being as cold as it is, the water in the system drops to about 115 before the burner fires again. Only gets up to about 160 to satisfy the thermostat.

 

[Dana]

At a boiler temp of 160F the average water temp on the radiation is about 150F, which would mean 85 feet of FineLine 30 would be emitting about 32-34,000 BTU/hr. If that's the temp where it's stabilizing, it means the burner has probably been downfired to 38,000 BTU/hr, substantially lower than the 110,000 BTU/hr the boiler was designed for. That probably takes a couple percent off it's steady state efficiency, but less of an efficiency hit than short-cycling a 110K burner.

The heat content per unit volume of #2 oil is about 50% more than propane, so if you're accustomed to the volume/month numbers of oil, the volume/month for propane at the same amount of heat is going to seem like it's going through a lot. In most local markets propane is also more expensive heat than #2 oil, but not all.

 

[Scott McNab]

Right now it's $1.05 per liter for oil and I pay $.63 per liter for propane. I have last winters oil numbers so I'll have to compare with this winters propane. Of course a different boiler too. I guess if it's more expensive I'll have to find an experienced hydronic installer to help find a solution to find better efficiencies. Thought was going with a propane boiler would save me some money.

 

[Dana]

Right now it's $1.05 per liter for oil and I pay $.63 per liter for propane. I have last winters oil numbers so I'll have to compare with this winters propane. Of course a different boiler too. I guess if it's more expensive I'll have to find an experienced hydronic installer to help find a solution to find better efficiencies. Thought was going with a propane boiler would save me some money.

At those prices the heating cost is you'd be better off spending the money on cold climate ductless mini-split heat pumps than a condensing propane boiler.

The 1-ton Fujitsu 12RLS3H delivers over 15,000 BTU/hr @ -20C, and about 12,000BTU/hr @ -25C. They make a 1.5 ton and a 0.75 ton versions too. A pair of the 1 tonners would deliver about the same amount of heat as your boiler at it's current burner settings. In my neighborhood the 1-tonners cost about USD$3800-$4000 each, all-in, fully installed & commissioned with warranty. A DIY installation can cost less than USD$3K, including the cost of a service call from a refrigeration tech to install the refrigerant and check the performance.

At -20C their coefficient of performance (COP) is about 2.0, and about twice that at -10C. A COP of 2 means for every kwh of power in you get 2 x 3412BTU/kwh= 6824 BTU/kwh.

A liter of propane has about 24,170 BTU source energy, burned at 85% efficiency delivers about 20,545 BTU of heat into the house.

So at -20C it takes 20,545/6824= 3 kwh to deliver the same amount of heat into the house as a liter of propane. Does your electricity cost more than $0.63/3= 21 cents/kwh?

In most of Ontario it's less than 15 cents.

At 15 cents/kwh during the shoulder seasons heating with mini-splits would cost less than half what it costs with $0.63/liter propane.

Mitsubishi's FHxxNA minisplits are roughly comparable in heating capacity as the Fujitsu xxRLS3H. Somewhere between -28C to -32C the Mitsubishi units can turn them selves off to self protect when their outdoor temperature sensor is out of range, but will automatically re-start at -25C. If you have the propane burner as backup that's not a disaster, but if you didn't some other backup would be a serious consideration in a climate as cool as yours.

Fujitsu units don't have that issue, and will keep running at -30C or cooler and still putting out heat, though the heating capacity isn't specified at temperatures below -26C. I know of one guy in Quebec heating his house with four earlier-generation 3/4 ton Fujitsu 9RLS2H who is satisfied with their capacity & performance at -30C. The newer generation versions have better capacity and efficiency than his.