@lebusmagique, you can replace your foot warmer with this: WR4000 - Products - Aqua-Hot Hydronic Heating
The only problem is that it needs 3/4 inch hose. I have been unable to find even a single new heater with one inch hose. Most manufacturers make only heaters with 5/8ths hose. I have found 2 retailers so far that have a few heaters with 3/4ths inch hoses.
Aqua-Hot makes a total of 4 models that come with 3/4 inch hoses. The one I linked above is the smallest. The others go up to 30,000 BTUs. But I have concerns about Aqua-Hot. They want you to prurchase by phone and I don't normally give out my phone number, especially to retailers. Retailers normally get a disposible email.
Aside from Aqua-Hot, all I have found so far is that Fisheries Supply has one heater made by Red Dot that is available in both 5/8ths and 3/4ths. There are several other Red Hot heaters listed on Fisheries Supply, but all the others come only in 5/8ths hose size.
I have already removed both heaters from my passenger compartment. I intend to replace them with one after market heater. I would like to replace both the front heaters too, just because they are 25 years old now. I will continue my search for heaters with one inch coolant connections, but I am not very optimistic about finding any. If anyone could point me to a source I would be very grateful.