Baseboards and Panel Radiators

[Alfa]

I am getting a new Buderus boiler to supply my baseboard heating system. One of the small baseboard sections is in the way of a proposed new cabinet in the kitchen. Can that one baseboard be replaced with a Buderus panel radiator (which would take up less room)? Can baseboard and panel radiators be mixed in the same circuit and heating system?

 

[Jadnashua]

Baseboard tends to have a non-linear heat output. A panel radiator tends to be more linear. Sized properly for your supply temperatures and heat loss, yes, you can mix them.

 

[Sponsor]

 

[Dana]

I am getting a new Buderus boiler to supply my baseboard heating system. One of the small baseboard sections is in the way of a proposed new cabinet in the kitchen. Can that one baseboard be replaced with a Buderus panel radiator (which would take up less room)? Can baseboard and panel radiators be mixed in the same circuit and heating system?

Yes you can mix them. At water temps of 120F and above the non-linear aspects of low-height fin-tube are negligible and the panel rad can be treated as "equivalent baseboard". At water temps of 100F and lower the difference become more apparent, but it's unlikely you'd be able to run the boiler that cool with fin-tube without short cycling anyway.

If you haven't already bought & installed the boiler (or even if you have), read this bit o' bloggery to figure out how low into the condensing zone you'd be able to go without short-cycling the boiler on your existing zone radiation, and this one to figure out the maximum size boiler is really needed. For most homes in Worcester all oil-fired boilers (including all Buderus oil boilers) are sub-optimally oversized for the space heating load, and the smallest SSB85 gas boiler has only a 5: 1 turn down, with a minimum firing rate of 17,000 BTU/hr is susceptible to short cycling on low-mass fin tube at condensing temperatures.

A fire-tube condensing boiler with a 10: 1 turn-down ratio such as the Lochinvar KHB-085 or HTP UFT-080W is usually a better bet, especially for low mass radiation like fin-tube baseboard.

 

[Alfa]

Dana, are you suggesting that I should have gone the propane/condensing boiler route? I looked into that but decided that replacing oil with oil was easier and more affordable.
The links you sent are interesting. I hope my installer knows what he is doing.
Thank you both for your responses.

 

[Dana]

Condensing propane is still substantially more expensive than oil.

Run the fuel-use load numbers as outlined in the blog, and measure up all the baseboard (zone by zone totals, if zoned). Some installers will size the boiler to the total amount of baseboard (which is almost always a mistake) to the tune of 500-600 BTU/hr per foot of baseboard rather than the heating demands of the house. Very often the baseboard was longer than needed for the house even before the house got storm windows (or double-pane replacements), and insulation in the walls and attic.

Typical oversizing factors in Worcester seem to run around 3x-4x (rather than the ASHRAE recommended 1.4x), which has efficiency consequences. With smarter controls much of those efficiency hits can be mitigated, but the smaller the boiler, the easier/better that is.

The smallest of the line Buderus G115WS/3 could (theoretically) heat my 2400' house + 1600' basement to 70F at an outdoor temperature of -80F, a temp not seen in Worcester since the last ice age. The G115WS/4 would have me covered down to -120F or so. As ridiculous as that is there are more G115WS/4s being installed out there than G115WS/3s. To even emit the full output of the G115WS/3 takes about 170 feet of baseboard- with less baseboard than that it will cycle on/off taking a loss in efficiency even when all zones are calling for heat.

Don't upsize the boiler to cover domestic hot water heating with an indirect fired tank either- just give the water heater priority with the zone controller. The recovery time with 85,000 BTU/hr of boiler behind it is already about 1/3 the time it takes for a gas or propane standalone water heater. By the time you've stepped out of the shower, dried off and gotten dressed it's done. The temperature in the house won't drop in any meaningful way when holding off the heat for 5-10 minutes to serve the water heater.