Electric Baseboard BTU per foot vs. Hot Water baseboard

I'm looking to get a coal boiler to replace electric baseboard heat in my approx 2000 square foot house. Right now I have a Hitzer 354 in the living room, but we really want to put in a coal boiler and rip out the electric baseboard and replace with HW baseboard since we're often away with no one to tend the Hitzer twice a day. Coal boiler my dad could stop by every 2-3 days to fill the hopper at least and dump the ashes.

I can't seem to find the answer as to what the BTU output per foot of electric baseboard typically is? Mine is hard wired 220 volt, lot of 4 foot and 8 foot strips in various rooms. I'd guess it's from the late 1980s or so. When running these hard I've had $800 a month electric bills, before I bought the hand-fired Hitzer as a stop-gap until we can get a boiler up and running.

I saw somewhere that electric baseboard is rated at 1085 BTU per foot? Seems like the high output Slant Fin 80 units are only rated at 750 BTU per foot with 180 degree water at 4 gallons per minute flow. That seems like a big difference.

I'm trying to figure out how much baseboard I'll need, it seems even the high-output hot water baseboard is much lower BTU than electric per foot, so I'm guessing I'll need a LOT more hot water baseboard vs. the electric baseboard I have now? Or should I run the coal boiler at like 195 degree water temps to make sure the baseboard pushes enough heat? I know Pex isn't supposed to go over 180 degrees so maybe I'll have to plumb with all copper to get enough oomph out of these hydronic baseboard units?

I think this discussion would be most helpful to your questions about electric vs hydronic baseboard.

BTU 'Rule of Thumb' (Stolen From Electric Baseboard 'ROT')

It contains calculations and suggestions for calculating based on heatloss/heatload instead.

I agree and suggest you do a heatload calculation per room first, then determine BTUs required.

There are different types of radiant heat and different output baseboards.

You *can* run hotter water for more BTUs, but you're better off to add radiation if you can, or use a different type radiant than to count on hotter output. But nothing wrong with copper, LOL.

Hope this helps.

Most of the 240v 4ft units I have seen are 1000 watts, which makes them 3412 btu's hr (853 btus/hr per ft). With 190 degree water, the Slantfin 80 baseboard you mentioned would be comparable in output. Hyden 958 baseboard would be slightly more.

With that said, it is possible that you have more electric baseboard than necessary, especially if the home has been improved since the baseboard was installed. I suggest downloading the Slantfin heat loss calculator and going through the steps to calculate the heat loss of each room.

https://www.slantfin.com/slantfin-heat-loss-calculator/

Thanks for the replies guys. My house is an early 1800s farmhouse that's had a couple additions tacked on over the years, poorly insulated and the windows are nothing special (wood frame Andersons that are probably from the mid 1980s).

Honestly the Slant Fin 80 baseboard units aren't that expensive in the grand scheme of things, so I may just go a bit overboard and run more than necessary. I'm also thinking of a small Modine hydronic unit heater for the basement, which right now is totally unheated and hovers in the mid 40s to high 30s all winter, and turns the upstairs floors into ice cubes.

A boiler in the basement will really warm things up. My basement is uninsulated, and about 900 sq.ft. Even with insulation and jackets my EFM keeps the basement around 72.

Nothing wrong with the SlantFin product, but Hyden makes nice baseboard as well. I would call around and compare pricing. If all else fails, Supplyhouse.com has SlantFin.

You can always check out baseray too. Awesome product, more durable, hold heat longer, but also takes longer to heat... Food for thought.

I'm going to take a stab at the average 220-240V single phase electric baseboard delivering ~200 Watt Hours of heat per foot of baseboard. That is the electrical equivalent of ~682 BTUH per foot. I believe the typical hot water baseboard is rated at ~500 BTUH per foot for 170 degree water (which is what you will average if you start with 180 degree water at the boiler and return 160 degree water to the boiler), so on a heat per linear foot basis roughly 1-1/3 feet of average Joe hot water baseboard will equal 1 foot of average Joe electric baseboard.

BTUH = BTU's per hour
Watt Hours = Watts per hour
1 Watt = 3.412 BTU's
1 KW = 3,412 BTU's
1 KWH = 3,412 BTUH

As a general rule of thumb you don't want to exceed ~52 feet of HWB (or alternately about 170 EDR, or "effective" Sq-ft of Cast Iron Radiator surface area) on a single zone loop. This is so the heat loss across the zone (the temperature drop, or Delta-T) can be kept at or near the industry standard target of 20 degrees F. Once you exceed about 52 feet of HWB (or about 170 EDR of old fashioned cast iron radiators) on a single zone your temperature drop is likely going to exceed 20 degrees F. with an average circulator, and in keeping with standard velocity wear and velocity noise advice. In my house there are 38 to 43 feet of hot water baseboard on each individual zone. Averaging to ~41 feet per zone.

As opposed to electrical baseboards which uniformly give off about 680 BTU's per every foot, HWB's (and cast iron radiators) give off progressively less heat for every foot, since the water in baseboard foot 2 is a wee bit cooler than baseboard foot 1, and foot 3 is a bit cooler than foot 2, etc....

Therefore it might be wise to short the first baseboards on a zone by some percentage (10% would be pure guessing) since they will see 180 degree water, keep the middle of the zones HWB's straight to calculation, and lastly increase the length of the tail end of the zones baseboards (the ones seeing closer to 160 degrees, by again a guess of 10%). I would ask an HVAC guy if they have rules of thumb for this sort of thing (or a better ballpark guess than my pure guess of 10%).

In my house they did not follow the above suggestion, as each room is amazingly right close to its computed feet of HWB required per sq-ft of floor space, regardless of if is the room seeing the 180 degree water or the room seeing the 160 degree water. And it still works well, but it could always be better...

Edit: If HWB's are rated for 550 BTUH per foot of 180 degree water, 500 BTUH per foot for 170 degree water, and 450 BTUH per foot for 160 degree water, then my guess of ~10% shortening/lengthening at the extreme ends of the zone seems like it should be pretty close to correct. And I do believe this to be how they are commonly rated.

550 x 0.9 = 495 BTUH per avg foot for the first users
500 x 1.0 = 500 BTUH per foot for the middle users
450 x 1.1 = 495 BTUH per foot for the tail end users

Pretty close in my book.

In a older 1800s house with poor insulation I would think about cast iron radiators for comfort and btu output.

If I'm looking at it correctly, 3-1/4 "effective" Sq-ft (or 'EDR') of cast iron radiator surface ~= 1 linear foot of HWB on an equivalent heat output basis. But a lot of that sq-ft is vertical, so cast iron baseboards likely take up much less wall space than do HWB's.

I agree that cast iron radiators are a particularly nice touch for an older house (or any house for that matter). Finding them, finding them in the correct size(s) needed for each room, and finding the ones that don't leak due to old age is the difficult part, as may be hustling many hundreds of pounds of radiators up and down stairs. New ones are way too expensive. I know they still sell mfg. and sell them in the UK.

I upgraded this old farm house's series zone with monoflow tees to a split supply and split return.

Essentially, I just ran a new 1" supply line to the far end of the zone and to the approximate middle of the baseboard run, cut a piece out of the existing 3/4" connector between sections and tee'd in a 3/4" x 3/4" x1" as the new supply.

I did the same on the close side for the return. Add a ball valve to adjust/balance the flow in case of different resistances and such in the new halves.

This gives a HIGHER AVERAGE temp to more baseboard to help overcome the "far end of the loop is always cold or doesn't heat" problem.

That and I used split tees to supply and return each zone off the main 1.5" loop. Also helps keep a higher average temp in the zone and keeps the main loop hotter.

It can still be slammed, but not very often- especially if the house is already warmed up and the DHW is up to temp. It can easily maintain temps so far in the coldest weather.

Slantfin has High Output line baseboards, too.

A kickspace heater is an interesting option, but I've not used one yet.

Be sure to leave enough room below baseboard for easy airflow with floor, carpeting, whatever.

A common old rule of thumb for poorly insulated homes with electric baseboard heating was to install 10 watts per sq-ft of floor space for each room. That is the same as 34 BTU's per sq-ft. For electric baseboards yielding 200 Watts per foot that should equate to 1 foot of electric baseboards required for every 20 sq-ft of a rooms floor space.

500 average BTU's per foot of HWB divided by 34 BTU's per sq-ft = 1 ft of HWB for every 14.7 sq-ft of floor space (for 8 foot ceilings).

A look at your area indicates that it has roughly 5,750 average annual HDD's (heating degree days) so I would think this old rule of thumb to have some potential for overkill, but if there is little in the way of tightness and insulation it may prove to be OK.

At 1-1/3 foot of HWB for every foot of electric baseboards (as I had derived earlier, as seen above) you would have 20 sq-ft/1.3333 = 15 sq-ft, so my earlier measure of 1 foot of HWB for every 15 sq-ft of floor space comes in at a pretty close check to the ballpark rule of thumbs 1 foot of HWB's for every 14.7 sq-ft. Don't forget to count closets and hallways as floor space.

Laery, why use a rule of thumb when there is free software that allows for the dimensions, number of windows, etc?

Rob R. wrote: ↑

Fri. Feb. 15, 2019 7:50 pm

Larry, why use a rule of thumb when there is free software that allows for the dimensions, number of windows, etc?

Rob, I agree. The software or a professional heat loss calculation (going rate ~$130, or so I'm told) would be best.

The SlantFin software is free to use.