What’s your heat bill a month

Nickkendall

I have a 36x 60 house with floor heat 3/4 tubes 18” centers  been heating it with a 9 kw boiler and costing about 200$ a month  for heat   I am now adding a 32x56 garage with 3/4 pex 18”      So I will be heating roughly 4000sq feet      So a rough thought is 4000 x 50 btu loss = 200,000 btu boiler   This seems high but I want fast recovery time when doors opened  and would sooner be on oversize as I will be adding another 30x30 lean to 
this was my first attempt at heating as I built my own house and did everything except electrical  so any help is Greatly appreciated 

Intplm.

@Nickkendall That is a very tough question to answer considering all the variables that exist.
Prices are very different from all over the country and around the world.
Members and viewers of this site come from all over the globe.

And as a rule of this site, we are also not allowed to discuss pricing.

hot_rod

50 btu is a very high guesstimate The home is possibly in the 20’s if the shop is well insulated it could also be in that range also

Remember the slab is a huge flywheel as soon as the door closes the space will warm back up quickly. I’d guess the load for both spaces closer to 100,000.

A load calc would help pinpoint the numbers.

Big Ed_4

You can more for your cable bill. Enjoy the Winter , it all most over ...

GroundUp

As was mentioned, it's very subjective. Location, construction, insulation, local utility rates, etc all play a role. Your 9 kw boiler is only 31,000 BTU (15 BTU per sq ft, not 50) and you'd be less than doubling the space so..... In theory, 60k would be adequate assuming the building construction is the same. There is a way to calculate heat loss of the space, you can't just throw a "BTU per sq ft" figure at it. For example, I heat a 40x40x14 shop and a 32x48x10 garage both with electric boilers and radiant slabs in MN; it's currently -24*F outside. My electric rate is around $.13/kwh (one kw equals 3412 BTU, these numbers are relative) and I can keep both buildings heated to 55 degrees all winter for about $300/mo average meaning I use approximately 7.9M BTU per month which averages out to about 11,000 BTU per hour. The heat loss of my big shop is calculated out to just under 40k if I remember correctly (at design temp of -20F) and the garage came in at under 20k as it's super insulated. There's a method to the madness, it's just a matter of proper system design.

Nickkendall

GroundUp said:

As was mentioned, it's very subjective. Location, construction, insulation, local utility rates, etc all play a role. Your 9 kw boiler is only 31,000 BTU (15 BTU per sq ft, not 50) and you'd be less than doubling the space so..... In theory, 60k would be adequate assuming the building construction is the same. There is a way to calculate heat loss of the space, you can't just throw a "BTU per sq ft" figure at it. For example, I heat a 40x40x14 shop and a 32x48x10 garage both with electric boilers and radiant slabs in MN; it's currently -24*F outside. My electric rate is around $.13/kwh (one kw equals 3412 BTU, these numbers are relative) and I can keep both buildings heated to 55 degrees all winter for about $300/mo average meaning I use approximately 7.9M BTU per month which averages out to about 11,000 BTU per hour. The heat loss of my big shop is calculated out to just under 40k if I remember correctly (at design temp of -20F) and the garage came in at under 20k as it's super insulated. There's a method to the madness, it's just a matter of proper system design.

I currently have a 15 kw boiler  and have plans of adding more ceiling insulation to get to r 50-60 to go along with with r26 walls  I have 8-10” of foam board 4’ down that I installed around perimeter  with 2” under slab aswell trying to get as insulated as possible. 
So what is the method to getting a Efficient system like you have   Getting the right boiler size and flow rate?
Tubes are

hot_rod

You building is what dictates the amount of heat required and the related cost. Always the best money you can spend is upgrading the building shell. The thermostat on the wall really doesn't know or care what the outdoor condition is, it just wants to maintain the inside condition.

Something often missed is infiltration. See if you can have a blower door test performed, sometimes utility companies offer that service as part of a weatherization project. If not it is worth paying for. You might be amazed when the computer spits out how large of an opening in square inches your home or shop has to the great outdoors.
Can lights, kitchen vent hoods, bathroom fans, insulation detail around plugs and switches, weatherstrips around doors, are the main leakage. Overhead garage door seals are another tough insulation detail.

A look at the inside and outside with an Infrared camera may shock you also, it clearly shows insulation and infiltration concerns.

Once the building is tightened up, next look at the most efficient way to convert your fuel to heat energy.The lowest possible supply temperature is going to be the most efficient way to move the energy, period. Many hydronic controls can watch and adjust that, I feel the indoor reset and feedback is the key, indoor and outdoor reset even better. You want to add the heat to the space at the exact same rate it is losing heat, at the lowest possible temperature. Setback is not a good match with radiant panel heat.

Obviously opening and closing shop doors is going to cost, really no way around that.
With radiant, as soon as the door closes the heat bottled up in the slab, travels at the speed of light to warm any cold objects you bring in. The space ambient temperature will recover quickly. It is a huge difference compared to ceiling mounted forced air, in that regard.

Nickkendall

Thanks for the great answers   I think I am going to invest in a thermal gun   

Nickkendall

How does that work if I want to add heat at the same rate it is lost  as I’m assuming it’s lost at a constant nonstop rate and I don’t want my boiler running nonstop?  Say I loose 100,000 btu and hr and I get 100,000 btu heater does that mean it would be running nonstop?

hot_rod

Nickkendall said:

How does that work if I want to add heat at the same rate it is lost  as I’m assuming it’s lost at a constant nonstop rate and I don’t want my boiler running nonstop?  Say I loose 100,000 btu and hr and I get 100,000 btu heater does that mean it would be running nonstop?

Exactly if the heat loss is perfectly matched to heat input it will run non stop. Both my boilers are running non stop these past weeks. Good news is they are mod cons running around 45- 60% firing. So a 110 boiler running 1/2 output. The shop is a one zone load so it is true that a boiler can and does run non stop when dialed in properly. Both boilers are Lochinvar, very easy to dial  in accurately.