ᐅ Heating two bathrooms of 3.5 m² each – General heating question

Hello,

we are currently finalizing the purchase of a house and are still completely undecided about the heating system. The old oil heating, which is 50 years old, needs to be removed along with all the pipes and radiators.

So far, we have been considering a heat pump combined with a wood stove with a water jacket.

For that, we would need or want to retrofit underfloor heating on about 65m2 (700 sq ft) on the ground floor.
The total cost for this would be around 80,000€.

Now there is the idea of using split air conditioning units for heating, and in the large room on the ground floor also a conventional wood stove for atmosphere and cold days.
This would save us a significant amount of money on installing the entire heating system, but we face one problem.

How should we then heat the two small bathrooms? They are each 3.5m2 (38 sq ft) and should be the warmest rooms in the house at 22°C (72°F).

Do you have any ideas on how to implement something sensible here?

Many thanks and best regards

Many people use electric towel warmers for this.

Alternatively, you can simply skip that and leave the bathroom door open. That’s how I know it from my youth, and that’s how we do it now as well. After showering, quickly dry off and get dressed, and everything works out fine.

Thank you,

both bathrooms are adjacent to hallways that will be heated very minimally. So, no heat would really enter from there.

You can’t install an indoor unit of a split system in the bathroom, right? Of course, drafts are definitely counterproductive, but the unit wouldn’t have to run while showering, rather to provide heating before and after. Or is that not possible because of the humidity?

A conventional electric heater would probably be very expensive if it had to keep the bathrooms constantly at 22°C (72°F).

Kind regards

Towel warmers are typically used as a supplementary heating source. With underfloor heating, the issue is that the bathroom usually has very limited surface area but potentially requires the highest temperatures.
And 3.5m² (38 sq ft) is not much. Heating for about half an hour in advance with a good fan heater is probably sufficient. One idea for morning showers would be to connect it to a timer set shortly before the alarm clock. I don’t have much to say about the split air conditioning system.

Matzl88 schrieb:

A conventional electric heating system would definitely be very expensive if it had to maintain the bathrooms constantly at 22°C (72°F).

Electric heaters are usually only operated when the bathroom is in use. Look into infrared heaters—they are suitable for this purpose. There are even mirrors that have built-in heating.

Matzl88 schrieb:

For that, we would or want to retrofit underfloor heating on about 65m² (700 ft²) on the ground floor.
The total cost would be around €80,000.

Now the idea came up to heat with split air conditioning units and to use a traditional wood stove in the large room on the ground floor for atmosphere and cold days.

That can definitely work. How big is the house? How many rooms and how many square meters?
The house is probably at least 50 years old, or even older, right? What is the overall energy condition like?

There are multi-split systems with up to 4 indoor units, and nowadays there are also unobtrusive indoor units shaped like picture frames, which might be a solution for the bathrooms. They measure about 60cm (24 inches) per side, square. Alternatively, ceiling-mounted indoor units could be used if the ceiling is or will be suspended anyway. They will certainly be oversized for a 3.5m² (38 ft²) bathroom, but you need some way to heat it.
I wouldn’t recommend heating the bathroom only “indirectly” through adjacent rooms. First, it’s uncomfortable and better the other way around; second, it causes moisture problems. The dampest room being the coldest is not a good idea.

The lower the energy demand—that is, the better insulated—the easier it is to maintain temperature and even install infrared panels there.
With an energy standard from around 1970, I would still add insulation (roof insulation, possibly from the inside, and at least internal insulation in the bathroom if there isn’t full facade insulation).

If you roughly calculate: bathroom with 3.5m² (38 ft²) and 150 kWh per m² in an uninsulated old building results in about 500 kWh heat demand per year.
Direct heating with infrared: 500 kWh electricity
Via split system with SCOP = 4: 125 kWh electricity
The difference of 375 kWh equals savings of about €100 in 2022 and €150–200 in the coming years. I would rather install a small indoor unit there.

Direct electrical heating is only viable without high follow-up costs if the energy demand per m² is low.
The approach using split air conditioners (+ domestic hot water heat pump) makes sense.
If you compare €80,000 with the cost of 2 multi-split systems with 4 indoor units each (2 * €10,000) plus a domestic hot water heat pump (€4,000), and also consider that less electricity is needed (the SCOP of multi-split systems is significantly better than heat pumps in old buildings with high supply temperatures), the choice is clear. For comfortable radiant heat in the living area, add a wood stove (without a water jacket but with plenty of thermal mass or even a tiled stove) and you’re done.

I had considered doing this during a planned renovation as well, but the purchase didn’t happen… the seller still hasn’t had success with their price expectations, and currently, the price trend for older properties is downward overall.