High efficiency vs high temp baseboard

skipboo24

I had a hvac company look at my set up. Most of the baseboard needs to be replaced because it is damage pretty bad. The guy said the high efficiency is a good choice because it runs at 120 f instead 180f. But the boiler is older and it's efficiency is 85%. Would the high efficiency be a good choice with this boiler. I will post more info of the boiler once have a chance it is at a house I am redoing. This is a oil boiler but his thought was someone day when this boiler dies then in the future it could be replaced to a high efficiency propane boiler if the baseboard was replaced to the high efficiency now.

PC7060

I’m not sure what he means by high-efficiency baseboards. If you want to transmit more heat you’ll have to have more transmissive heat surface which means larger panels. If you elected to put large radiator panels you may be able to run lower supply water temperature  which would work well with a condensing boiler. 

If the contractor is proposing to put the same size baseboards,  I don’t really see how it will make any difference from your current configuration.

bburd

Sounds like the contractor is proposing high output baseboard, with about 50% more heat output per linear foot than the standard stuff.

The first step here is a heat loss calculation on the house, a.k.a. “manual J“. If thermal upgrades have been done to the house since those baseboards were installed, like replacement windows or added insulation, these will have reduced the load. There’s no reason to buy more baseboard element than you need.

Also, full heat output is only needed on the coldest days. If the system can be kept within condensing return temperatures most of the time, there’s no need to size the baseboards to do so on the coldest days.

EdTheHeaterMan

Cold return temperature will help reduce the life of the oil fired boiler. If the boiler only needs to produce 120° water to operate efficiently, then the minimum 130° return temperature will never happen unless you have a bypass to keep the boiler temperature say at 145° and then a mixing valve to the radiators at the lower temperature. Then the lower temperature return water from the new radiators, can mix with the 145° bypass boiler water to have the recommended 130° minimum return temperature for your existing boiler.

But if you don't have the proper near boiler piping, then that existing oil fired boiler will suffer from corrosion resulting from condensation of flue gasses. This may be the plan, or may be an oversight from the contractor. the result will still be the same. A leaking boiler before its time.

hot_rod

Do the room by room heat load calculation first. Be interesting to know how the boiler is size3 to realistic load.

If you go with high output fin tube you could decrease the lineal feet required if that appeals? Check the cost difference however. I like the different look of some of the high output board better.

Possibly an outdoor reset control to regulate boiler operating temperature and offer return temperature protection.
https://www.slantfin.com/slantfin-heat-loss-calculator/

mattmia2

hot_rod said:

If you go with high output fin tube you could decrease the lineal feet required if that appeals? Check the cost difference however. I like the different look of some of the high output board better.

Some of it is a lot sturdier than residential grade baseboard too.

HomerJSmith

The only way to get more heat {BTU's) out of a given length of fin tube baseboard is to increase the temp of the water flowing thru it and or increase the flow at a given water temp, both up to a point.

When heated water flows thru a baseboard some of the heat (BTU's) radiate in to the room so that the entering water temp(EWT) is higher than the exiting (returning) water temp(RWT). If your baseboard is in series which most all are by the time you get to the last baseboard in the series, the EWT can be many degrees lower with lower heat emitted into the room.

Using hi efficiency baseboard, non fan assisted, operating at 120 deg ain't a gona happen with a cast iron boiler. The RWT must be a minimum of 130 degs to prevent acidic flue condensation.

It's not a simple as choosing hi efficiency over standard baseboard and expecting to run the sys at 120 degs. A lot of factors must be taken into consideration.

If you are considering replacing the boiler with a high efficiency boiler in the near future, you can opt for high efficiency, but be aware that the high efficiency will operate at higher temp and that would produce more heat until the new boiler is installed, but the thermostat will cut the boiler off when the thermostat reaches set point. In other words, operating a baseboard at 180 deg can be a smaller radiating area than one operating at 120 degs which has to be larger to produce the same BTU's in the room.